USMLE 1 MCQ2

Discussion in 'USMLE STEP 1' started by Guest, Jun 8, 2005.

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    <1>A 37-year-old female presents to the emergency room with a fever.
    Chest x-ray shows multiple patchy infiltrates in both lungs.
    Echocardiography and blood cultures suggest a diagnosis of acute
    bacterial endocarditis limited to the tricuspid valve. Which of
    the following is the most probable etiology?
    A. Congenital heart disease
    B. Illicit drug use
    C. Rheumatic fever
    D. Rheumatoid arthritis
    E. Systemic lupus erythematosus

    Answer
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    <2>Which of the following is the primary opsonin in the complement system?

    A. C1q
    B. C3b
    C. C5
    D. C5a
    E. Factor B

    Answer
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    <3>A patient is referred to a neurologist because of ataxia. Neurological
    examination reveals a loss of proprioception and a wide-based, slapping gate
    Magnetic resonance imaging reveals degeneration of the dorsal columns and
    dorsal roots of the spinal cord. Which of the following organisms is most
    likely to have caused this pattern of damage?

    A. Haemophilus influenzae
    B. Herpes simplex I
    C. Neisseria gonorrhoeae
    D. Neisseria meningitidis
    E. Treponema pallidum


    Answer
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    <4>A 24-year-old woman in her third trimester of pregnancy presents with
    urinary frequency and burning for the past few days. She denies fever,
    nausea, vomiting, or chills. She takes no medications besides prenatal
    vitamins and is generally in good health. Physical examination is
    remarkable for mild suprapubic tenderness, and a urine dipstick is
    positive for white blood cells, protein, and a small amount of blood.
    Culture produces greater than 100,000 colonies of gram-negative
    bacilli. Which of the following attributes of this uropathogenic
    organism is most strongly associated with its virulence?


    A. Bundle-forming pili
    B. GVVPQ fimbriae
    C. Heat labile toxins
    D. Heat stable toxins
    E. P pili
    F. Type 1 pili


    Answer
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    <5>A previously healthy 11-year-old girl develops a gastrointestinal
    infection with cramping and watery stools. After several days, she begins
    to pass blood per rectum, and is hospitalized for dehydration. In the
    hospital, she is noted to have decreasing urine output with rising blood
    urea nitrogen (BUN). Total blood count reveals anemia and
    thrombocytopenia, and the peripheral smear is remarkable for
    fragmented red cells (schistocytes). Infection with which of
    the following bacterial genera is most likely responsible fo
    r this syndrome?


    A. Campylobacter
    B. Clostridium
    C. Salmonella
    D. Shigella
    E. Vibrio



    Answer
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    <6>Five days after returning to his military base in South Carolina after
    survival training in the nearby countryside, an 18-year-old recruit reports
    to the infirmary complaining of a headache. Physical examination reveals a
    fever, but no other abnormalities are noted. A few days later he returns
    to the infirmary with a maculopapular rash involving the hands and feet.
    The rash then spreads centripetally to involve the trunk. Which of the
    following diseases should be suspected?


    A. Chickenpox
    B. German measles
    C. Measles
    D. Mumps
    E. Rocky Mountain spotted fever



    Answer
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    <7>A 32-year-old, blood type A positive male receives a kidney transplant
    from a blood type B positive female donor with whom he had a 6-antigen HL
    A match. Once the kidney is anastomosed to the man's vasculature,
    the transplant team immediately begins to observe swelling and
    interstitial hemorrhage. After the surgery, the patient developed
    fever and leukocytosis and produced no urine. Which of the following
    is the most likely explanation?
    A. Acute rejection due to antibody-mediated immunity
    B. Acute rejection due to cell-mediated immunity
    C. Chronic rejection due to cell-mediated immunity to minor HLA antigens
    D. Hyperacute rejection due to lymphocyte and macrophage infiltration
    E. Hyperacute rejection due to preformed ABO blood group antibodies


    Answer
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    <8>A sexually active 18-year-old woman presents with a fever of 102 F for
    the past 24 hours and lower abdominal pain and anorexia for the past 5 days.
    On physical examination, there is generalized tenderness of the abdomen,
    and the cervix is erythematous with motion tenderness. There is no rash
    nor any lesions on the external genitalia. A smear of the odorless
    cervical discharge contains sloughed epithelial cells and scant
    neutrophils. Which of the following would likely be found in the
    exudate?


    A. A naked, icosahedral double-stranded circular DNA virus
    B. Iodine-staining intraepithelial inclusion bodies
    C. Intraneutrophilic gram-negative diplococci
    D. Intranuclear "owl's eye" inclusion bodies
    E. Lactose-fermenting gram-negative bacilli
    F. Pear-shaped flagellated protozoa
    G. Pleomorphic, gram-negative rods
    H. Spirochetes on dark-field microscopy


    Answer
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    <9>A 45-year-old homeless man has a chronic cough, a cavitary lesion of the
    lung, and is sputum positive for acid-fast bacilli. Which of the following
    is the principle form of defense by which the patient's body fights this
    infection?


    A. Antibody-mediated phagocytosis
    B. Cell-mediated immunity
    C. IgA-mediated hypersensitivity
    D. IgE-mediated hypersensitivity
    E. Neutrophil ingestion of bacteria


    Answer
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    <10>A 15-year-old girl in a rural community has swollen, painful lymph nodes
    in her right axilla. Physical examination reveals multiple scratches on her
    right arm with a papule associated with one of the scratch marks. She
    states that the scratches occurred about 5 days ago. What type of animal
    is the most likely source of the infection?


    A. Cat or kitten
    B. Chicken
    C. Dog or puppy
    D. Horse
    E. Parrot


    Answer
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    <11>A 38-year-old AIDS patient presents to the clinic complaining of nausea,
    occasional vomiting and "bumps" on his groin. On physical examination,
    multiple, nontender, pedunculated reddish purple nodules in the inguinal
    and perirectal areas are observed. The patient's liver is palpable 8 cm
    below the right costal margin. Routine laboratory tests are unremarkable
    except for an alanine aminotransferase level of 58 and alkaline
    phosphatase of 90. He denies any foreign travel, but has two pet cats
    . Which of the following is the most likely cause of this patient's
    infection?


    A. Bartonella henselae
    B. Human papillomavirus
    C. Molluscum contagiosum virus
    D. Rickettsia prowazekii
    E. Treponema pallidum

    Answer
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    <12>A 49-year-old Vietnamese man is diagnosed with tuberculosis. On physical
    examination, large flocculent masses are noted over the lateral lumbar back
    , and a similar mass is located in the ipsilateral groin. This pattern of
    involvement strongly suggests an abscess tracking along the
    A. adductor longus
    B. gluteus maximus
    C. gluteus minimus
    D. piriformis
    E. psoas major

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    Answer
    <13>A 25-year-old man presents with a high fever and generalized malaise.
    His condition deteriorates so rapidly that his friends decide to take him
    to the emergency department 24 hours after the onset of symptoms. He has a
    history of intravenous drug abuse. A test for anti-HIV antibodies is
    negative. Physical examination reveals a systolic murmur, and
    echocardiography shows bulky vegetations attached to the tricuspid valve
    leaflets. Which of the following microorganisms will be most likely be
    isolated from this patient's blood cultures?
    A. Candida albicans
    B. Hemophilus influenzae
    C. Staphylococcus aureus
    D. Staphylococcus epidermidis
    E. Viridans (a-hemolytic) streptococci
    Answer
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    <14>A 23-year-old man develops explosive watery diarrhea with blood, fecal
    leukocytes, and mucus approximately 3 days after eating chicken that was
    improperly cooked. Comma-shaped organisms were found in the fecal smea
    r along with red blood cells and leukocytes. Which of the following
    pathogens is the most likely cause of these symptoms?
    A. Campylobacter jejuni
    B. Enterotoxigenic E. coli
    C. Shigella sonnei
    D. Staphylococcus aureus
    E. Vibrio cholera

    Answer
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    <15>An otherwise healthy 3-year-old child is brought to the pediatrician
    with umbilicated, flesh-colored papules on his trunk. This condition is
    related to infection with which of the following viruses?
    A. Cytomegalovirus
    B. Herpesvirus 6
    C. Parvovirus
    D. Poxvirus
    E. Variola
    Answer
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    <16>A 47-year-old male presents with declining renal function characterized
    by oliguria, elevated blood urea nitrogen and creatinine, and hematuria .
    He also complains of nasal congestion and epistaxis. Review of systems is
    notable for occasional cough and hemoptysis. Examination shows mucosal
    ulceration and nasal septal perforation, but no polyps. Which of the
    following serum markers would likely be present in this case?
    A. Anti-centromere antibody
    B. Anti-Ro
    C. Anti-SS-B
    D. c-ANCA (cytoplasmic antinuclear cytoplasmic antibody)
    E. Decreased erythrocyte sedimentation rate (ESR)
    Answer
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    <17>A child with sickle cell anemia is seen in a hematology clinic. Her
    mother states that she has been feeling very tired lately, and may have
    "come down with a virus." On physical examination, the girl is very pale,
    and a complete blood count shows severe anemia. A bone marrow aspirate
    contains no erythroid precursor cells. The girl was probably infected
    with which of the following viruses?
    A. Coxsackie virus
    B. Echovirus
    C. Hepadnavirus
    D. Herpes virus
    E. Parvovirus
    Answer
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    <18>Zygomycosis, a destructive fungal infection of the sinuses, is likely to
    reach the brain by which of the following routes?
    A. Cavernous sinus
    B. External carotid artery
    C. Internal carotid artery
    D. Superior sagittal sinus
    E. Superior vena cava
    Answer
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    <19>A newborn in the neonatal intensive care unit becomes tachypneic and
    irritable. Blood cultures grow a gram-positive coccus in chains that is
    presumed to be a streptococcus. Which of the following characteristics
    would help to differentiate Streptococcus agalactiae from Streptococcus
    pneumoniae?
    A. Alpha-hemolysis
    B. Carbohydrate capsule
    C. Cytochrome enzyme system
    D. Growth in bile
    E. Oxacillin sensitivity
    Answer
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    <20>A 16-year-old girl presents with a painlessly enlarged lymph node in her
    right axilla. Peripheral blood counts are within normal limits. The lymph
    node is biopsied, and numerous granulomas filled with neutrophils and
    necrotic debris are observed. Which of the following organisms could
    produce this disease?
    A. Bartonella henselae
    B. Borrelia burgdorferi
    C. Chlamydia psittaci
    D. Coxiella burnetii
    E. Rickettsia prowazekii
    Answer
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    <21>A 36-year-old mother of two children presents with a 4-day history of
    swollen, painful hands. Her wrists and metacarpophalangeal joints are
    boggy and inflamed bilaterally. Her 5-year-old son had been sent home
    from school approximately 3 weeks previously with red cheeks and a
    blotchy rash on his torso. What is the most likely diagnosis?
    A. Listeriosis
    B. Lyme disease
    C. Mumps
    D. Parvovirus
    E. Reiter's syndrome
    Answer
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    <22>A 37-year-old, intravenous drug-abusing male presents with fever and
    chills. Blood cultures are positive for Staphylococcus aureus. He develops
    central nervous system symptoms, and a cerebral abscess is suspected.
    Which part of the brain is most often affected by septic emboli in
    patients with infective endocarditis?
    A. Brainstem
    B. Cerebellum
    C. Frontal lobe
    D. Occipital lobe
    E. Parietal lobe
    Answer
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    <23>Which of the following organisms is the most common cause of
    community-acquired pneumonia?
    A. Chlamydia pneumoniae
    B. Haemophilus influenzae
    C. Mycoplasma pneumoniae
    D. Staphylococcus aureus
    E. Streptococcus pneumoniae
    Answer
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    <24>One week following a visit to the woods along an Eastern seaboard beach,
    a 50-year-old woman develops fever, headache, chills, and fatigue. A blood
    smear demonstrates protozoa within erythrocytes. Which of the following is
    the most likely pathogen?
    A. Babesia microti
    B. Leishmania donovania
    C. Plasmodium falciparum
    D. Plasmodium vivax
    E. Trypanosoma cruzi
    Answer
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    <25>A 20-year-old female presents with a two day history of dysuria and
    increased urinary frequency. She states that she was recently married and
    was not sexually active prior to the marriage. Physical exam reveals a
    temperature of 100.7 °F with normal vital signs. Gynecological exam reveals
    no evidence of discharge, vaginitis, or cervicitis. Urinalysis reveals 14
    white blood cells per high-powered field with many gram-negative rods.
    The most appropriate therapy would be
    A. ampicillin
    B. ceftriaxone
    C. fluconazole
    D. gentamicin
    E. metronidazole
    Answer
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    <26>An active intravenous drug abuser presents to the emergency department
    with fever of 5 days' duration, a cough occasionally productive of blood,
    and pleuritic chest pain. Petechiae are present in his mouth and
    conjunctivae, and splinter hemorrhages are visible under the fingernails.
    Which of the following test results would most likely confirm the identity
    of the causative agent?
    A. Antibodies to p24 capsid antigen
    B. Antibodies to Trichinella spiralis antigen
    C. Blood culture of a catalase-positive, novobiocin-sensitive, gram-positive coccus
    D. Blood culture of a coagulase-positive, catalase positive, gram-positive coccus
    E. Blood culture of a gamma-hemolytic, gram-positive coccus on bile-esculin agar
    F. Blood culture of an alpha-hemolytic, optochin-resistant, gram-positive coccus
    G. Blood culture of an alpha-hemolytic, optochin-sensitive, gram-positive coccus
    Answer
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    <27>A 43-year-old executive presents to a physician with chronic, symmetric
    polyarthritis involving the knees. The man gives a history of having
    developed an extensive rash after a deer hunting trip in Connecticut
    several years earlier. He tells that he felt "sick" at the time,
    and developed knee pain that prevented him from climbing stairs for
    several months, but then partially resolved. Which of the following
    organisms is most likely etiologically related to the patient's
    arthritis?
    A. Fungus
    B. Gram-negative cocci
    C. Gram-negative rod
    D. Gram-positive cocci
    E. Spirochete
    Answer
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    <28>A 34-year-old woman presents with fatigue, malaise, and swollen, tender
    joints. Physical examination is significant for a maculopapular eruption
    over sun-exposed areas, including the face. Examination of a peripheral
    blood smear reveals mild thrombocytopenia. Which of the following
    autoantibodies, if present, would be most specific for the diagnosis of
    the patient's disorder?
    A. Anti-centromere antibody
    B. Anti-IgG antibody
    C. Antinuclear antibody
    D. Anti-Sm (Smith antigen) antibody
    E. Anti-SS-A (Ro) antibody
    Answer
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    <29>A 33-year-old single mother of two young children visits her physician
    because of an oral ulcer. A review of systems is significant for fatigue,
    myalgia, and joint pain. Laboratory results demonstrate leukopenia, and
    a high-titered antinuclear antibody. A speckled staining pattern due to
    anti-Sm is seen with immunofluorescence; urinary protein is elevated.
    Which of the following is the most likely diagnosis?
    A. Generalized fatigue
    B. Goodpasture's syndrome
    C Mixed connective tissue disease
    D. Scleroderma
    E. Systemic lupus erythematosus
    Answer
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    <30>A 67-year-old black man with a history of glucose-6-phosphate
    dehydrogenase (G-6-PD) deficiency presents with fever, irritative voiding
    symptoms, and perineal pain. Rectal examination is remarkable for a boggy,
    exquisitely tender prostate. A urine Gram's stain is positive for
    gram-negative rods. The risk for development of hemolytic anemia is
    highest if he receives high-dose, 21-day therapy with
    A. ampicillin
    B. cefaclor
    C. ciprofloxacin
    D. sulfamethoxazole/trimethoprim
    E. tetracycline
    Answer
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    <31>A patient with colorectal cancer develops septicemia complicated by
    endocarditis. You would expect the blood cultures to grow
    A. Streptococcus agalactiae
    B. Streptococcus bovis
    C. Streptococcus pneumoniae
    D. Streptococcus pyogenes
    E. Streptococcus viridans
    Answer
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    <32>A patient with a cavitary lung lesion coughs up sputum that contains
    thin, acid-fast positive rods. Which of the following features would most
    likely be associated with these bacteria?
    A. Nutritional requirement for factors V and X
    B. Streptokinase
    C. Toxic shock syndrome toxin
    D. Visible under dark field illumination
    E. Waxy envelope

    Answer
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    <33>A 27-year-old woman presents to the emergency department complaining of
    10-12 episodes of nonbloody diarrhea per day for the past 2 days, along
    with severe abdominal cramps, nausea, vomiting, and a low-grade fever.
    She states that she just returned from a vacation to Mexico. While in
    Mexico, she did not drink any of the local water and ate only cooked
    foods and a few fresh salads. If fecal leukocytes are present, the
    patient should most likely be empirically treated with
    A. acyclovir
    B. ciprofloxacin
    C. mebendazole
    D. quinine
    E. tetracycline

    Answer
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    <34>A 54-year-old woman suffering from influenza deteriorates and develops
    shaking chills and a high fever. Physical examination is remarkable for
    dullness to percussion at the left base and decreased breath sounds on
    the left. Chest x-ray confirms the diagnosis of lobar pneumonia, presumed
    to be caused by Streptococcus pneumoniae. The patient has no known drug
    allergies. Which of the following antibiotics would be most appropriate
    to treat the patient's condition?
    A. Cefotaxime
    B. Chloramphenicol
    C. Erythromycin
    D. Penicillin
    E. Vancomycin
    Answer
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    <35>A 4-year-old boy is seen by his pediatrician for epistaxis. The patient
    has a history of multiple bacterial and viral respiratory tract infections
    and eczema. An uncle had similar problems. Physical examination is
    remarkable for multiple petechial lesions on the skin and mucous
    membranes. Serum IgE is increased, and platelets are decreased.
    Which of the following is the most likely diagnosis?
    A. Acquired hypogammaglobulinemia
    B. Ataxia telangiectasia
    C. DiGeorge syndrome
    D. Selective IgA deficiency
    E. Wiskott-Aldrich syndrome
    Answer
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    <36>Which of the following organisms is most likely to be implicated as a
    cause of urethritis that persists after antibiotic therapy for gonorrhea?
    A. Actinomyces
    B. Chlamydia
    C. Mycobacteria
    D. Nocardia
    E. Rickettsia
    Answer
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    <37>A 73-year-old woman with a history of diabetes presents with left ear
    pain and drainage of pus from the ear canal. She has swelling and tenderness
    over the left mastoid bone. Which of the following microorganisms is the
    most likely causative agent?
    A. Hemophilus influenzae
    B. Klebsiella pneumoniae
    C. Mucor sp.
    D. Pseudomonas aeruginosa
    E. Streptococcus pyogenes
    Answer
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    <38>: A 25-year-old female presents with a confluent maculopapular rash that
    began on her face, then spread downward over her trunk. She states that 3
    days ago she started having a fever and headache, with bilateral pain
    associated with the front and back of her neck. She also complains of
    joint pain. Which of the following diseases does she most likely have?
    A. Infectious mononucleosis
    B. Lyme disease
    C. Roseola
    D. Rubella
    E. Rubeola
    Answer
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    <39>A 24-year-old woman presents with a 3-day history of fever, chills, chest
    pain, and cough productive of rust-colored sputum. Past medical history
    includes a splenectomy 1 year ago. A chest x-ray film indicates
    consolidation of the right lower lobe. Blood cultures are positive for
    a-hemolytic gram-positive diplococci. Immunity to the causative organism
    is based on
    A. alternative complement pathway activation
    B. antibody to an a-helical coiled fimbria
    C. IgA antibodies to C carbohydrate
    D. IgG antibodies to C carbohydrate
    E. IgG antibodies to a surface acidic polysaccharide
    Answer
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    <40>A 3-year-old male presents with a skin rash and epistaxis. He has had
    several, severe sinopulmonary infections. A careful history reveals that
    his maternal grandfather died of bleeding complications following an
    emergency cholecystectomy. What additional findings are likely in this
    case?
    A. A CD4/CD8 ratio of < 1.5:1
    B. Cerebellar ataxia
    C. Elevated platelet count and high serum IgG, IgA, and IgE levels
    D. Low platelet count and low serum IgG levels
    E. Low platelet count and low serum IgM levels
    Answer
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    <41> Which of the following characteristics most strongly suggests that
    the cell depicted above is a phagocytically active macrophage?
    A. Immunocytochemical detection of collagenase
    B. Microvilli-covered surface
    C. Presence of receptors for IgG and complement
    D. Presence of secondary lysosomes throughout cytoplasm
    E. Shape of the nucleus
    Answer
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    <42>A 27-year-old white male presents with a 3-week history of several
    swollen and painful toes and knees. He has a past history of conjunctivitis. He also describes some low back stiffness that is more severe in the morning. Which of the following is the most likely diagnosis?
    A. Gout
    B. Lyme disease
    C. Reiter's syndrome
    D. Rheumatoid arthritis
    E. Septic arthritis
    Answer
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    <43>A 1-year-old girl presents with a 2-day history of fever,
    vomiting, and watery, nonbloody diarrhea. On physical exam, she
    appears dehydrated. Which of the following best describes the
    most likely infecting organism?
    A. It has a complex double-stranded DNA genome
    B. It has a partially double-stranded circular DNA genome
    C. It has a segmented, double-stranded RNA genome
    D. It has a single-stranded circular RNA genome
    E. It has a single-stranded RNA genome
    Answer
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    <44>A 46-year-old woman visits her podiatrist to have several bunions
    removed from her right foot. She chooses conscious sedation rather
    than general anesthesia for this procedure. She is given intravenous
    midazolam to supplement the local anesthetics that are injected into
    her foot. Midway through the surgery, she suddenly becomes agitated,
    combative, and exhibits involuntary movements. The anesthesiologist
    determines that she is having a paradoxical reaction to the midazolam
    and immediately administers
    A. flumazenil
    B. glucagon
    C. naloxone
    D. nitrite
    E. protamine
    Answer
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    <45>A 24-year-old woman attempts suicide by taking an overdose of diazepam.
    She is rushed to the emergency department, where the attending physician
    will most likely order which of the following treatments?
    A. Acetylcysteine
    B. Atropine
    C. Bicarbonate
    D. CaNa2EDTA chelation
    E. Deferoxamine
    F. Ethanol
    G. Flumazenil
    H. Physostigmine
    I. Pralidoxime
    J. Protamine
    Answer
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    <46>Which of the following enzymes is stimulated by glucagon?
    A. Acetyl-CoA carboxylase
    B. Glycogen phosphorylase
    C. Glycogen synthase
    D. HMG-CoA reductase
    E. Pyruvate kinase
    Answer
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    <47>A 29-year-old epileptic sanitation engineer is maintained on primidone.
    Ultrastructural examination of a liver biopsy reveals increased amounts of
    smooth endoplasmic reticulum. This change is most closely related to
    increases in the activity of which of the following?
    A. P-450 system
    B. Purine degradation
    C. Pyrimidine synthesis
    D. Tricarboxylic acid (Krebs) cycle
    E. Urea cycle
    Answer
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    <48> A pregnant southeast Asian immigrant presents for prenatal
    care. Her past medical history is significant for a severe illness 3
    years ago characterized by fatigue, nausea, anorexia, vomiting, jaundice,
    joint pains, and generalized skin lesions that slowly disappeared. She
    has felt well recently. Which of the following laboratory tests should
    be ordered to investigate the patient's past illness?

    A. Hepatitis B surface antigen (HBsAg)
    B. IgG cytomegalovirus (CMV) antibody levels
    C. IgM antibody to HBsAg
    D. IgM antibody to hepatitis B core antigen
    E. Quantitation of hepatitis A virus (HAV) IgM antibody
    Answer
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    <49>A research scientist is studying calcium fluxes in cultured cells
    using confocal laser scanning microscopy. The magnitude of the signal
    (brightness) is proportional to the strength of the calcium flux.
    Stimulation of which of the following receptor types would be expected
    to produce the strongest signal?
    A. Alpha-1 adrenergic receptor
    B. Beta-1 adrenergic receptor
    C. Dopamine-1 receptor
    D. Muscarinic acetylcholine receptor
    E. Nicotinic acetylcholine receptor

    <50>A 10-year-old child is suspected of having pellagra because of chronic
    symptoms including diarrhea, a red scaly rash, and mild cerebellar ataxia.
    However, his diet is not deficient in protein and he appears to be
    ingesting adequate amounts of niacin. A sister has a similar problem.
    Chemical analysis of his urine demonstrates large amounts of free amino
    acids. Which of the following is the most likely diagnosis?
    A. Alkaptonuria
    B. Carcinoid syndrome
    C. Ehlers-Danlos syndrome
    D. Hartnup's disease
    E. Scurvy
    Answer
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    Answers
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    1>The correct answer is B. The most probable etiology of bacterial endocarditis involving the tricuspid valve is illicit intravenous drug use, which can introduce skin organisms into the venous system that then attack the tricuspid valve. Staphylococcus aureus accounts for between 60% and 90% of cases of endocarditis in intravenous drug users.
    The endocarditis associated with congenital heart disease (choice A) typically involves either damaged valves or atrial or ventricular septal defects. The tricuspid valve is not particularly vulnerable.
    Rheumatic fever (choice C) most commonly damages the mitral and aortic valves, and tricuspid damage is usually less severe and seen only when the mitral and aortic valves are heavily involved. Consequently, secondary bacterial endocarditis involving only the tricuspid valve in a patient with a history of rheumatic fever would be unusual.
    Rheumatoid arthritis (choice D) is not associated with bacterial endocarditis.
    Systemic lupus erythematosus (choice E) can produce small, aseptic vegetations on valves, but is not associated with bacterial endocarditis.
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    2>The correct answer is B. C3b is the most critical molecule in both the classical and alternative complement pathways. C3, the most abundant protein of all the complement proteins, is cleaved into C3a and C3b. C3b attaches to bacterial surfaces for opsonization by phagocytes. C3a binds to mast cells and basophils, activating them and producing histamine release.
    C1q (choice A) is a complement component in the classical pathway. It binds to the constant heavy domain of an IgG molecule that has reacted with the bacterial surface epitope. C1q is not involved in opsonization as it simply functions as an enzyme in the early complement cascade.
    C5 (choice C) is a protein, that once split into C5b, initiates the assembly of the membrane attack complex. This complex consists of C5b, C6, C7, C8, and polymerization of C9, and is responsible for lysis of the bacteria. C5a is a strong chemotactic molecule.
    This fragment is the result of C5 being split by the C5 convertases of both pathways. This C5a (choice D) is a strong chemotactic factor for neutrophils and results in stimulating the inflammatory response.
    Factor B (choice E) is an activator protein of the alternative pathway. It combines with C3b to form C3bBb. This C3bBb is the C3 convertase of the alternative pathway.
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    3>The correct answer is E. The findings described are those of tabes dorsalis, a form of tertiary syphilis caused by Treponema pallidum. Tabes dorsalis, and other forms of tertiary syphilis, are now uncommon in this country, possibly because the common use of antibiotics may "treat" many unsuspected cases of syphilis.
    Haemophilus influenzae (choice A) and Neisseria meningitidis (choice D) can cause meningitis.
    Neisseria gonorrhoeae (choice C) causes gonorrhea, which usually does not involve the CNS.
    Herpes simplex I (choice B) can cause an encephalitis that typically involves the frontal and temporal lobes.
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    4>The correct answer is E. Urinary tract infections are the most common bacterial infections encountered during pregnancy, and Escherichia coli is the most commonly isolated organism. 70% of cases in the U.S. are caused by P pili-positive strains.
    Bundle-forming pili (choice A) are found in enteroaggregative E. coli (EAEC).
    GVVPQ fimbriae (choice B) are found in EAEC.
    Heat labile toxins (choice C) are pathogenic factors in enterotoxic strains (ETEC).
    Heat stable toxins (choice D) are pathogenic factors in ETEC or EAEC.
    Type 1 pili (choice F) are a major pathogenic factor in ETEC.
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    5>The correct answer is D. This patient has developed hemolytic-uremic syndrome (HUS), a complication of the Shiga toxin or Shiga-like toxin: exotoxins released by Shigella species and the enterohemorrhagic E.coli. HUS in children usually develops after a gastrointestinal or flu-like illness, and is characterized by bleeding, oliguria, hematuria and microangiopathic hemolytic anemia. Presumably the Shiga toxin is toxic to the microvasculature, producing microthrombi that consume platelets and RBCs, and may fragment the red cell membrane.
    The incorrect choices are all bacteria which may produce an enterocolitis, but do not elicit HUS.
    A long-term consequence of Campylobacter (choice A) infection is a reactive arthritis or full-blown Reiter's syndrome.
    Clostridial enterocolitis is produced by Clostridium difficile (choice B), a normal inhabitant of the gut that produces pseudomembranous colitis when other gut flora are suppressed by treatment with antibiotics.
    In the United States, Salmonella infections (choice C) are almost all non-typhoid inflammatory diarrhea, producing a simple enterocolitis that may proceed to sepsis in some cases. Typhoid fever (produced by Salmonella typhi and S. paratyphi) produces a protracted illness that progresses over several weeks and includes rash and very high fevers, but not HUS.
    Vibrio (choice E) infections produce copious amounts of watery diarrhea, and the major risk of cholera and other Vibrio enteritides is shock due to hypovolemia or electrolyte loss.
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    6>The correct answer is E. Take rashes involving the palms and soles (otherwise unusual sites) very seriously: only a small number of infections can cause this pattern, including Rocky Mountain spotted fever, meningococcemia, and secondary syphilis. Rocky Mountain spotted fever is caused by the rickettsia R. rickettsii, and is found throughout the United States, particularly in south central and eastern portions (not the Rocky Mountains). 3-12 days after a tick bite, patients develop malaise, frontal headache, and fever. Several days later, the rash described in the question stem develops. Other manifestations can include hepatosplenomegaly, thrombocytopenia, and (potentially fatal) disseminated intravascular coagulation.
    Chickenpox (choice A), or varicella, is characterized by maculopapules that evolve into vesicles over hours to days, then eventually form crusts. Typical lesions first appear on the trunk and face and rapidly spread to involve other areas.
    The maculopapular rash of German measles (choice B), or rubella, usually begins on the face, then spreads down the body.
    Although the maculopapular rash of measles (choice C), or rubeola, can include the palms and soles, it typically begins along the hairline in frontal and temporal regions, then spreads down the trunk to the limbs.
    Mumps (choice D) is characterized by fever, malaise, parotitis, and orchitis, but not a rash.
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    7>The correct answer is E. The patient is suffering from hyperacute rejection due to the preformed anti-B ABO blood group antibody found in all type A positive individuals. Hyperacute rejection occurs within minutes to a few hours of the time of transplantation, and is due to the destruction of the transplanted tissue by preformed antibodies reacting with antigens found on the transplanted tissue that activate complement and destroy the target tissue. Preformed antibodies can also be due to presensitization to a previous graft, blood transfusion, or pregnancy.
    Acute rejection due to antibody-mediated immunity (choice A) is incorrect because this patient suffered from hyperacute rejection (immediate) occurring within minutes to hours, rather than days.
    Acute rejection due to cell-mediated immunity (choice B) will not occur until several days or a week following transplantation. Acute rejection is due to type II and type IV reactions.
    Chronic rejection, due to the presence of cell-mediated immunity to minor HLA antigens (choice C), occurs in allograft transplantation months to even years after the transplant. Chronic rejection is generally caused by both humoral and cell-mediated immunity.
    An accelerated acute rejection, occurring in 3-5 days, can be caused by tissue infiltration and destruction by presensitized T lymphocytes and macrophages (choice D) and/or antibody-dependent, cell-mediated cytotoxicity (ADCC). Note that this is not a hyperacute reaction.
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    8>The correct answer is B. The presentation is typical for pelvic inflammatory disease (PID). Chlamydia trachomata (serotypes D-K) is the most common bacterial cause of sexually transmitted disease (STD) in this country and is the most likely agent on the list to produce the symptoms described. It is an ATP-defective organism that must therefore live intracellularly in the human host and can be visualized inside epithelial cells with iodine, Giemsa, or fluorescent-antibody stains. The remainder of the answer choices refer to other agents that could be found in the female genital tract, either by sexual transmission or by contamination with fecal flora, but they are not the best choices.
    A naked, icosahedral double-stranded circular DNA virus (choice A) refers to human papilloma virus, which is the most common cause of STDs in the U.S., but presents with anogenital warts.
    Intraneutrophilic gram-negative diplococci (choice C) refers to Neisseria gonorrhoeae, which would be expected to present with dysuria and neutrophilic exudate.
    Intranuclear "owl's eye" inclusion bodies (choice D) refers to cytomegalovirus, a common STD in the United States, but not a common agent of PID. Most cases in average adults are manifested by mononucleosis-like symptoms.
    Lactose-fermenting gram-negative bacilli (choice E) would be consistent with Escherichia coli. Although this organism is the most common cause of urinary tract infections in women in the United States, it would not be expected to cause PID.
    Pear-shaped flagellated protozoa (choice F) refers to the protozoan parasite Trichomonas vaginalis, the only protozoan STD in the world. Infection would be characterized by a malodorous, cheesy exudate, and there would be more erythema of the external genitalia than of the cervix.
    Pleomorphic, gram-negative rods (choice G) are consistent with Hemophilus ducreyi, which causes chancroid, and presents in a different manner.
    Spirochetes on dark-field microscopy (choice H) refers to Treponema pallidum, the causative agent of syphilis, which would produce rash and/or chancre, depending on the stage of the infection.
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    9>The correct answer is B. The principle host defense in mycobacterial infections (such as this patient's tuberculosis) is cell-mediated immunity, which causes formation of granulomas. Unfortunately, in tuberculosis and in many other infectious diseases characterized by granuloma formation, the organisms may persist intracellularly for years in the granulomas, only to be a source of activation of the infection up to decades later.
    While antibody-mediated phagocytosis (choice A) is a major host defense against many bacteria, it is not the principle defense against Mycobacteria.
    IgA-mediated hypersensitivity (choice C) is not involved in the body's defense against Mycobacteria.
    IgE-mediated hypersensitivity (choice D) is not involved in the body's defense against Mycobacteria. It is important in allergic reactions.
    Neutrophil ingestion of bacteria (choice E) is a major host defense against bacteria, but is not the principle defense against Mycobacteria.
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    10>The correct answer is A. This patient has the classic symptoms of cat scratch disease caused by the bacillus Bartonella henselae. The disease is self-limited with the onset of symptoms occurring 3-10 days following an inoculating scratch. The organism can be isolated from kittens, typically less than 1 year of age, or from fleas. A history of a new kitten in the house and the papule at the site of a scratch with regional painful adenopathy defines the classic scenario.
    Chickens (choice B) can harbor Salmonella spp. producing a gastroenteritis or enterocolitis. Chicken guano is also a favorable environment for the fungus Histoplasma capsulatum. The mycelial phase thrives in the rich soil. The human disease is a granulomatous infection involving the lungs and mimicking tuberculosis.
    Dogs or puppies (choice C) carry Capnocytophaga canimorsus as part of the normal flora of the oral cavity. Infections from licking or biting range from a self-limited cellulitis to fatal septicemia. Patients at risk for more severe infections are those with asplenia, alcoholism, or hematologic malignancies. This organism is also associated with cat bites, but the patient develops cellulitis and fulminant septicemia, especially in asplenic patients. Pasteurella multocida is another pathogen that colonizes the nasopharynx and gastrointestinal tract of cats and dogs. Cats have the highest rate of colonization (50-90%), followed by dogs (50%), swine (50%), and rats (14%). P. multocida most commonly causes a localized soft tissue infection or cellulitis after an animal bite, but systemic symptoms may be present in about 40% of the cases. These symptoms include osteomyelitis, septic arthritis, or tenosynovitis.
    Horses (choice D) and horse manure have been associated with a pulmonary opportunistic infection with cavitation caused by Rhodococcus equi that resembles tuberculosis in immunocompromised patients. Burkholderia mallei (the cause of glanders) is characterized by non-caseating granulomatous abscesses of skin, lymphadenopathy, and pronounced involvement of the lungs.
    Parrots (choice E) are associated with psittacosis caused by Chlamydia psittaci. Psittacosis is associated with a dry, hacking cough productive of scant sputum, an interstitial infiltrate in the lungs, severe headache, and myalgias. A pale macular rash is also seen.
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    11>The correct answer is A. Bacillary angiomatosis is a disease that occurs primarily in AIDS patients, and is indicative of a defect in cell-mediated immunity. It is caused by either Bartonella henselae or Bartonella quintana. The domestic cat is the reservoir for these organisms and they are usually transmitted to humans via a cat scratch or cat bite. Patients with this illness usually have multiple skin lesions and extracutaneous manifestations involving liver and bone. Diagnosis is usually based on characteristic histopathologic findings including plump "epithelioid" endothelial cells and mitotic figures. A macrolide, such as erythromycin or azithromycin, is the drug of choice for the infection.
    Human papillomavirus (choice B) causes warts. Infection can present as a sessile wart or as condyloma acuminatum, which are fleshy soft growths that coalesce into large masses. When cellular immunity is depressed, as in AIDS, the condylomata acuminatum proliferate.
    Molluscum contagiosum virus (choice C) is a pox virus that is spread by close person-to-person contact. Infection produces a firm nodule that often becomes umbilicated, and may resolve by discharging its contents. In AIDS, the lesions do not resolve, but enlarge and spread.
    Rickettsia prowazekii (choice D) is the cause of epidemic typhus. It is spread by the human body louse, Pediculus humanis. Its reservoirs are humans and flying squirrels.
    Treponema pallidum (choice E) is the spirochete that causes syphilis. The characteristic primary lesion is a chancre (a painless, indurated ulcer) at the site of inoculation.
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    12>The correct answer is E. This is the classic presentation of a psoas abscess. This clinical entity was formerly a fairly common complication of vertebral tuberculosis, but is now rare in clinical practice in this country. The psoas muscle is covered by a fibrous sheath known as the psoas fascia. This sheath is open superiorly, permitting an infection involving the soft tissues around the spine to enter the sheath, then track down to the groin.
    The adductor longus (choice A) is a muscle of the anterior thigh, and is not related to the lumbar portion of the back.
    The gluteus maximus (choice B) gluteus minimus (choice C) and piriformis (choice D) are muscles of the buttock with no relationship to the groin.
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    13>The correct answer is C. The patient has a fever and is extremely ill. The most important clue to the diagnosis is the presence of bulky vegetations on the tricuspid valve, indicating that he has infective endocarditis. On the basis of the rapid clinical course, this is likely a case of acute infective endocarditis. The diagnosis of this condition must be confirmed by blood cultures, which are also necessary to determine bacterial antibiotic sensitivity. S. aureus (commonly present on the skin) is the most frequent etiologic agent of infective endocarditis in intravenous drug abusers. It commonly affects the tricuspid valve. Because of its high virulence, S. aureus-related endocarditis follows an acute course and may lead to death within a few days.
    The causative agents of infective endocarditis differ depending on host factors. Fungal organisms, such as Candida albicans (choice A), may cause infective endocarditis in severely immunosuppressed patients, such as those with AIDS.
    A minority of cases of infective endocarditis are caused by a number of normal commensals in the oral cavity, i.e., the "HACEK" group: Hemophilus (choice B), Actinobacillus, Cardiobacterium, Eikenella, and Kingella.
    S. epidermidis (choice D) and other coagulase-negative staphylococci tend to produce endocarditis in recipients of prosthetic valves.
    Viridans streptococci (choice E) are the most frequent agents causing endocarditis in previously abnormal valves, such as those damaged by rheumatic disease, or congenitally abnormal valves. Coagulase-negative staphylococci and viridans (a-hemolytic) streptococci are less virulent than S. aureus and are thus associated with a subacute (more prolonged) clinical course and a better prognosis
    --------------------------------------------------------------------------------
    14>The correct answer is A. Campylobacter jejuni is a pathogen causing an invasive enteric infection associated with ingestion of raw or undercooked food products, or through direct contact with infected animals. In the U.S., ingestion of contaminated poultry that has not been sufficiently cooked is the most common means of acquiring the infection. The patients typically have bloody diarrhea, abdominal pain, and fever. The presence of fecal leukocytes indicates an invasive infection. The organism is a gram negative rod with a "comma-shape."
    Enterotoxigenic E. coli (choice B) causes the classic traveler's diarrhea. The infection is non-invasive and is acquired via the fecal-oral route through consumption of unbottled water or uncooked vegetables. The major manifestation is a copious outpouring of fluid from the GI tract presenting as explosive diarrhea. This is due to the action of one of two types of enterotoxins on the GI tract mucosa.
    Shigella sonnei (choice C) produces a syndrome very similar to C. jejuni. However, the organism appears as a gram-negative rod on Gram's stain. It does not have a comma shape. Transmission is from person to person via the fecal-oral route. Infection requires a low infective dose since the organism is fairly resistant to gastric acidity.
    Staphylococcus aureus (choice D) produces food poisoning due to the ingestion of a pre-formed enterotoxin. The organism is present in food that is high in salt content such as potato salad, custard, milk shakes, and mayonnaise. The patient presents with nausea, vomiting, and abdominal pain, followed by diarrhea beginning 1-6 hours after ingestion of the enterotoxin.
    Vibrio cholerae (choice E) produces a secretory diarrhea due to increases in cAMP in the intestinal cells. The organism is not invasive. The patient presents with the sudden onset of painless, watery diarrhea that becomes voluminous, followed by vomiting. The stool appears nonbilious, gray, and slightly cloudy with flecks of mucus, no blood, and a sweet odor.
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    15>The correct answer is D. The lesions are characteristic of molluscum contagiosum, which is a typically benign and self-limited condition caused by a poxvirus. The disease can be transmitted either venereally or through non-venereal contact. The other viruses listed do not cause similar skin lesions. Patients with advanced HIV infection may develop a severe, generalized, and persistent eruption, often involving the face and upper body.
    Cytomegalovirus (choice A) causes congenital infections and disseminated infections in immunosuppressed patients.
    Herpesvirus 6 (choice B)causes roseola (exanthem subitum).
    Parvovirus (choice C) causes aplastic crises in patients with hemolytic anemia.
    Variola (choice E) is the smallpox virus.
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    16>The correct answer is D. This patient has Wegener's granulomatosis, which is characterized by renal involvement, severe upper respiratory tract symptoms, and pulmonary involvement. Other organ systems may also be involved. The renal syndrome is a crescentic rapidly progressive glomerulonephritis leading to renal failure. The upper respiratory tract findings include sinus pain and drainage, and purulent or bloody nasal discharge with or without nasal ulcerations. Nasal septal perforation may follow. Pulmonary involvement may be clinically silent with only infiltrates present on x-ray, or it may present as cough and hemoptysis. c-ANCA is a marker for Wegener's granulomatosis, present in a high percentage of patients.
    Anti-centromere antibody (choice A) is associated with approximately 90% of cases with CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal motility syndrome, sclerodactyly, and telangiectasia) which is also called limited scleroderma.
    Anti-Ro (choice B) is also called anti-SS-A and is associated with Sjِgren's syndrome (70-95%).
    Anti-SS-B (choice C) is associated with Sjِgren's syndrome (60-90%).
    Decreased ESR (choice E) is not a marker of Wegener's. Instead, a markedly elevated ESR is seen. Additionally, mild anemia, thrombocytosis, leukocytosis, mild hypergammaglobulinemia (IgA), and mildly elevated rheumatoid factor are seen in this disorder.
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    17>The correct answer is E. Parvoviruses are small single-stranded DNA viruses, of which only serotype B19 is pathogenic for humans. This virus causes three distinct syndromes: a childhood febrile rash known as erythema infectiosum ("Fifth disease"); aplastic crisis in individuals with chronic hemolytic diseases (sickle cell anemia, thalassemia, etc); and congenital infections that can present as stillbirth, hydrops fetalis (analogous to severe Rh incompatibility), or severe anemia.
    Coxsackie viruses (choice A) usually cause cold-like illness, but can cause herpangina, myocarditis, and meningitis.
    Echoviruses (choice B) can infect a variety of organ systems (GI, CNS, eyes, heart, respiratory, skin), but are not a cause of aplastic crises.
    Hepadnavirus (choice C) is the causative agent of hepatitis B.
    Herpes viruses (choice D) cause a variety of acute to chronic infections including herpes simplex types I and II, chicken pox, chronic herpes zoster, CMV infection, and Epstein Barr virus infections.
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    18>The correct answer is A. The cavernous sinuses are located on either side of the body of the sphenoid bone, and become a potential route of infection because they receive blood both from the face (via the ophthalmic veins and sphenoparietal sinus) and some of the cerebral veins. The spread of infection, especially by Mucor sp., into the cavernous sinus, can produce either CNS infection or cavernous sinus thrombosis, both of which are potentially fatal.
    The route from the face to the brain is not arterial (choices B and C).
    The superior sagittal sinus (choice D) is located in the falx cerebri, and drains venous blood from the brain to other dural sinuses, from which it eventually drains into the jugular vein. Zygomycosis does not reach the brain by way of the superior sagittal sinus.
    The superior vena cava (choice E) drains blood from the upper part of the body into the heart.
    --------------------------------------------------------------------------------
    19>The correct answer is A. Streptococci are usually initially speciated by their hemolytic capacity on sheep blood agar. Beta-hemolytic streptococci include groups A, B, and D. S. agalactiae is the classic group B streptococcus. The non beta-hemolytic streptococci consist principally of the pneumococci and the viridans group.
    Both S. agalactiae and pneumococcus have a carbohydrate capsule (choice B), an important virulence factor and means of subtyping streptococcal species.
    None of the streptococci utilize cytochrome enzymes (choice C). They derive all of their energy from the fermentation of sugars to lactic acid.
    Neither pneumococcus nor S. agalactiae can grow in bile (choice D). This ability is specific for the enterococcus group (group D) of streptococci.
    Both pneumococci and S. agalactiae are usually treated with penicillin-type antibiotics, although group B streptococci require a penicillinase-resistant type such as oxacillin (choice E).
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    20>The correct answer is A. Bartonella henselae is the infective agent of cat scratch disease, which generally presents as regional lymphadenopathy with or without low fevers and headaches. Bartonella is a gram-variable pleomorphic rickettsial organism that is introduced to the skin in a cat bite or scratch. It produces a self-limited granulomatous response in the draining lymph nodes.
    Borrelia burgdorferi (choice B) is a spirochetal organism that is transmitted by a tick bite (Ixodes spp.), producing Lyme disease. Lyme disease progresses from a skin rash to fevers, headache and pain over about one month. It may produce lymphadenopathy, but is not associated with granuloma formation.
    Chlamydia psittaci (choice C) infection occurs after contact with infected bird droppings and produces an atypical pneumonia. The central nervous system may also be involved, but lymph nodes are spared. Chlamydia trachomatis is the chlamydial species that typically produces suppurative nodal granulomas (lymphogranuloma venereum).
    Coxiella burnetii (choice D) infection is transmitted by inhaling dusts or drinking milk from infected mammals, especially sheep and cows. The disease in humans, Q fever, is marked by mild nonspecific symptoms or pneumonia, and may progress to myocarditis or hepatitis.
    Rickettsia prowazekii (choice E) produces epidemic (louse-borne) typhus, which is transmitted by body lice and produces a rash akin to Rocky Mountain spotted fever. Although the organism may reside in the lymph nodes in dormancy, it does not elicit granuloma formation.
    --------------------------------------------------------------------------------
    21>The correct answer is D. Parvovirus B19 causes erythema infectiosum, or Fifth disease. The 5-year-old boy has the classic "slapped cheek" appearance. Adults typically do not get the facial rash, but have arthralgias and arthritis. The symmetrical distribution of involved joints is similar to that in rheumatoid arthritis. The onset in adults is typically 3 to 4 weeks after exposure. Parvovirus infections may persist in immunosuppressed patients, resulting in red blood cell aplasia.
    Listeriosis (choice A) is caused by the gram-positive rod Listeria monocytogenes. Meningitis and bacteremia are common clinical manifestations. Elderly, neonates, pregnant women, and those taking steroids have the highest risk for infection.
    Lyme disease (choice B) is caused by Borrelia burgdorferi. It is the most common vector-borne disease (Ixodes ticks) in the U.S. The incidence is highest in the summer and fall. The white-footed mouse and the white-tailed deer are zoonotic reservoirs. From 3 to 32 days following a tick bite, the patient develops fever, lymphadenopathy, meningismus, and the characteristic rash (erythema migrans). The rash enlarges and resolves over 3 to 4 weeks. Sequelae include arthritis, carditis, and neurologic abnormalities.
    Mumps (choice C) is caused by a Paramyxovirus. The virus most commonly affects glandular tissue. Parotitis, pancreatitis, and orchitis are characteristic. Mumps meningoencephalitis is one of the most common viral meningitides. Mumps polyarthritis is most common in men between the ages of 20 and 30 years. Joint symptoms begin 1 to 2 weeks after the parotitis subsides and large joints are involved.
    Reiter's syndrome (choice E) is a seronegative, asymmetric arthropathy predominantly affecting the lower extremities. It may be triggered by a C. trachomatis infection. In addition to the arthritis, patients may have urethritis (which is usually due to chlamydia), conjunctivitis, mucocutaneous disease such as balanitis, oral ulcerations, or keratoderma. Approximately 80% of patients are HLA-B27 po
    --------------------------------------------------------------------------------
    22>The correct answer is E. Embolization from infective endocarditis typically causes multiple, small parietal lobe abscesses. This "factoid" is worth knowing because some patients with infective endocarditis present with what clinically looks like multiple small "strokes", and their treatable cardiac disease may be completely unsuspected.
    --------------------------------------------------------------------------------
    23>The correct answer is E. The most common bacteria implicated in community-acquired pneumonia is the pneumococcus, Streptococcus pneumoniae. Other organisms frequently implicated in patients less than age 60 without comorbidity include Mycoplasma pneumoniae, respiratory viruses, Chlamydia pneumoniae, and Haemophilus influenzae. When community-acquired pneumonia occurs in elderly patients or patients with comorbidity, aerobic gram-negative bacilli and Staphylococcus aureus are added to the list.
    The organisms listed in choices A, B, and C are important causes of community-acquired pneumonia, but are not the most frequent causes.
    Staphylococcus aureus (choice D) is an important cause of community-acquired pneumonia (particularly in the elderly and in patients with comorbidity), but is not the most frequent cause.
    --------------------------------------------------------------------------------
    24>The correct answer is A. The combination of a one week incubation period, the Eastern seaboard clue, and the intra-erythrocyte parasites strongly suggest Babesia microti as the infecting organism. The clinical disease is called babesiosis. The infecting protozoan is related to Plasmodium and is transmitted by the bite of the Ixodes dammini tick. Occasional cases have been transmitted by blood transfusions. Most patients are asymptomatic; symptomatic cases in reasonably healthy individuals have the features listed in the question stem. Rare severe cases, which may be fatal, may develop in severely debilitated or asplenic individuals and can be accompanied by severe hemolysis (up to 30% of RBCs may have the parasites) with subsequent hemoglobinuria, hemolysis, and renal failure.
    Leishmania donovania (choice B) is an intracellular tissue protozoan, not a blood protozoan.
    Plasmodium falciparum (choice C) and Plasmodium vivax (choice D) are malarial parasites not encountered on the Eastern seaboard.
    Trypanosoma cruzi (choice E) is an intracellular tissue protozoan, and does not infect blood cells.
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    25>The correct answer is A. The patient's presentation is consistent with a simple urinary tract infection; there is a short history of dysuria, increased urinary frequency and the appearance of white blood cells and gram-negative rods in the urine. Urinary tract infections are common in women after they become sexually active. The infection is likely caused by urethral trauma during intercourse, which leads to bacterial contamination of the bladder. Since the majority of these infections are caused by Escherichia coli (a gram-negative rod), the most appropriate therapy would be ampicillin for around 10 days.
    Ceftriaxone (choice B) is the treatment of choice for uncomplicated infections with N. gonorrhoeae, now that most strains are resistant to penicillin. Intravenous ceftriaxone is a regimen reserved for the treatment of life-threatening infections.
    Fluconazole (choice C) is indicated for the treatment of vaginal candidiasis. Since there is no vaginal discharge and the patient has gram-negative rods in the urine, a diagnosis of vaginal candidiasis can be excluded.
    Gentamicin (choice D) would be an i
  2. wutnext

    wutnext Guest

    can i get the answers from 26- 50
  3. ataafshar

    ataafshar Guest

    would u plz copy and paste answers for questions 26 to 50?
  4. Guest

    Guest Guest

    RE

    Hi

    I can't check the answers 26 to 50.
    When I open the link it said
    " The page ( www.aippg.net) you are trying to find does not exist, Please visit http://www.aippg.net/forum for AIPPG forums "
    If anyone knows the correct link, please let me know

    Thanks in advance
    Fuhua
  5. ata

    ata Guest

    let's dicide answers

    Hi all

    I can't still get the answers 25 to 50 anyway.
    Let's dicide it[/i]
  6. SUP man

    SUP man Guest

    Anyone in uk for usmle step studies

    EMAIL ME AT supman999@hotmail.co.uk.

    Will discuss and motivate each other to get a 99...what say??

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