USMLE Forum Archives - USMLE Step 1 - 2331
2331
babbu5508 - 12-31-10 00:27
A 6-week-old infant is brought to the emergency room with a 10-day history of coughing and choking spells. The white blood cell count is elevated with 80% lymphocytes. The child is gasping for breath, experiencing paroxysms of coughing, and vomits twice in the examination room. Encapsulated, gram-negative rods grow out on Bordet-Gengou media. Which of the following microorganisms is the likely cause of these symptoms?
Options:
A. Bordetella pertussis
B. Haemophilus influenzae
C. Klebsiella pneumoniae
D. Legionella pneumophila
E. Mycoplasma pneumoniae
babbu5508 - 12-31-10 00:27
A 6-week-old infant is brought to the emergency room with a 10-day history of coughing and choking spells. The white blood cell count is elevated with 80% lymphocytes. The child is gasping for breath, experiencing paroxysms of coughing, and vomits twice in the examination room. Encapsulated, gram-negative rods grow out on Bordet-Gengou media. Which of the following microorganisms is the likely cause of these symptoms?
Options:
A. Bordetella pertussis
B. Haemophilus influenzae
C. Klebsiella pneumoniae
D. Legionella pneumophila
E. Mycoplasma pneumoniae
The correct answer and explanation will be available after you answer.
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#4
Re: 2331
babbu5508 - 01-03-11 00:25 The correct answer is B. Entamoeba histolytica is an intestinal amoebic parasite that either can cause relatively mild diarrhea, or can behave more aggressively, causing dysentery (bloody diarrhea with abdominal pain and dehydration), peritonitis, or liver abscess formation (such as this patient has). Treatment is with metronidazole.
#5
Re: 2331 babbu5508 - 01-03-11 00:26 he correct answer is A. The child has whooping cough, or more accurately if one goes by the chronology of the symptoms, "coughing whoop," as the patient is subject to a series of coughing episodes that are followed by a rapid inspiration of air; the "whoop" is caused by the rapid passage of air through a narrowed airway. The infection of the respiratory tract by Bordetella pertussis causes a hyperreactivity of the respiratory apparatus; even the slightest stimulus will trigger a coughing episode. The offending pathogen excretes adenylate cyclase and also produces an exotoxin that inactivates the inhibitory subunit of the G-protein complex, thus activating adenylate cyclase within the cells of the respiratory system. Bordet-Gengou agar is the blood-enriched (15% vs. 5% for normal blood agar) medium used for the laboratory isolation of this pathogen. Fluorescent antibody testing is used to verify the diagnosis.
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