October 25, 2010

USMLE 1 Question 17

A 40yr old man visiting a coastal area had sea food for dinner consisting of oyster and shrimps. Next morning he developed severe abdominal pain, diarrhea, vomiting and fever.

The stools were blood stained. The man did not require any rehydration therapy and was treated with ciprofloxacillin and recovered in about 2 days.

These clinical features are typical of infection by

a) Vibrio cholerae
b) Vibrio parahaemolyticus
c) Vibrio vulnificus
d) Salmonella typhi
e) Rota virus

The correct answer is B

Vibrio parahaemolyticus is an important cause of gastroenteritis and food poisoning world wide. The gastroenteritis due to this organism is specifically and characteristically associated with the intake of sea food especially shrimps and oysters.

It causes an acute diarrheal disease within 24hrs of ingestion of the infected food. The patient develops severe abdominal pain, diarrhea, vomiting and fever. The stools in a severe infection maybe blood stained. The disease is more or less self limiting and is cured within 1-3 days.

Vibrio cholerae is incorrect since it causes a very severe gastroenteritis which has characteristically rice water stools and not blood stained stools. Also it has no association with consumption of sea food. The patient is severely dehydrated and if not rehydrated can die within hours.

Vibrio vulnificus also causes an infection after consumption of sea food but it is not the correct answer since it does not typically cause any gastrointestinal manifestations. The organism is absorbed quickly and causes a fatal septicemia.

Salmonella typhi does not typically cause an acute diarrheal disease. It does not manifest within 24hrs and has an incubation period of 7-14 days. Also it is a systemic infection and does not cause any gastrointestinal manifestations.

Rota virus causes mild diarrhea, usually in infants and children. It rarely infects adults. Also the diarrhea is very mild associated with little or no abdominal pain and rarely fever. It has no definite association with sea food

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