An 18-month old developed acute gastroenteritis with fever and watery diarrhea that lasted 10 days. She had been vaccinated against rotavirus at 2 and 4 months of age as recommended. Eight days later, both of her brothers, ages 3 and 6, developed acute gastroenteritis. Which of the following tests would most likely reveal the etiologic agent of their gastroenteritis?

The lack of vomiting, duration of her symptoms, and timing of onset of her brothers' symptoms described in the clinical vignette, and her up-to-date immunization against rotavirus strongly suggest that adenovirus is the etiologic agent. Therefore, an EIA for adenovirus types 40/41 (c) is the best test. Rotavirus and Norovirus infections can also be diagnosed by EIA; however, culture for Norovirus (a) is not available and serology for Rotavirus (e) would be expected to be positive due to her immunizations. An EM examination of stool for astrovirus (d) would not likely be available in most clinical settings, although EM can also reveal Rotavirus, Norovirus and other caliciviruses, and adenovirus. Enteroviruses, although they infect cells of the intestinal tract, do not usually cause acute gastroenteritis. A DFA for enterovirus on intestinal biopsy (b) would not likely be helpful in establishing the etiologic agent. See the table in the answer to question 114 for additional information.