Kaplan USMLE Step 1: Nausea, vomiting after a group dinner

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

Several family and friends come to the emergency department because of abrupt onset of chills, nausea and vomiting, and abdominal pain. A few hours earlier, they attended a wedding reception dinner that served pork, chicken, and fish entrees with asparagus and potatoes and various cream-filled pastries and custards. These individuals had no similar episodes prior to this event. A few individuals had to be admitted for rehydration. Leftover food was collected from all prepared dishes and sent for analysis. Which of the following is the most likely causal organism? 

A. Bacillus cereus 

B. Clostridium perfringens 

C. Escherichia coli 

D. Shigella sonnei 

E. Staphylococcus aureus

The correct answer is E.

Staphylococcus aureus food poisoning, caused by enterotoxin A, has a short incubation period (less than 6 hr), and presents with nausea, vomiting, and abdominal pain after consuming contaminated meat, poultry, or eggs.  Patients do not typically present with diarrhea. 

Choice A: This outbreak of food-borne illness is most likely caused by Staphylococcus aureus. Bacillus cereus would be more likely if the patients had been consuming rice.