Norovirus is the most common cause of viral gastroenteritis.  Symptoms include diarrhea, vomiting, fever, malaise, and headache.  The diarrhea is typically watery without blood or mucus due to lack of small bowel inflammation.

Norovirus (part of the Calicivirus family) possesses a linear, nonenveloped, single-stranded RNA genome.  It is resistant to inactivation by acid, bile, and pancreatic enzymes.  As a result, norovirus is easily transmitted via fecal-oral spread (eg, foodborne, person-to-person via contaminated bodily fluids) and results in outbreaks in crowded settings (eg, schools, hospitals, cruise ships, nursing homes).  The incubation period is 1-2 days; symptoms develop acutely and self-resolve within days.  The diagnosis is typically based solely on clinical presentation, but polymerase chain reaction testing may be performed to confirm an outbreak.

(Choice A)  Adenoviral gastroenteritis typically presents with fever and watery diarrhea.  Outbreaks can occur, but these are far less common than with norovirus.  Adenovirus more commonly causes pharyngoconjunctivitis and coryza (eg, runny nose, nasal congestion).

(Choice B)  Vomiting, high fever, and bloody diarrhea are typical of Campylobacter jejuni enteritis.  Transmission occurs via oral contact with contaminated food (eg, poultry) or drinks.  Outbreaks are not as common as those of viral etiology.

(Choice C)  Clostridioides (formerly Clostridium) difficile infection can result in asymptomatic carriers, pseudomembranous colitis, or fulminant colitis.  Patients have watery diarrhea with or without blood, abdominal pain, fever, and leukocytosis.  Prior antibiotic exposure (eg, fluoroquinolones, clindamycin) is the most significant risk factor.

(Choice D)  Enterotoxigenic Escherichia coli (ETEC), the most common cause of traveler's diarrhea, is prevalent in developing countries.  Although the acute onset of nausea, vomiting, and watery nonbloody diarrhea is typical of ETEC infection, it would be unlikely in patients who have not traveled abroad recently.

(Choice F)  Gastroenteritis outbreaks can also occur with rotavirus infection, with a presentation similar to that of norovirus.  However, the prevalence of rotavirus in developed countries has decreased dramatically since the introduction of routine childhood vaccination.  Rotavirus is unlikely in vaccinated children (as in this case).

(Choice G)  Salmonella typhi infection can result in typhoid fever and presents with fever, followed by abdominal pain and diarrhea and/or constipation.  Severe complications (eg, hepatosplenomegaly, intestinal perforation, sepsis) occur in a minority of patients.

Educational objective:
Norovirus is the most common cause of viral gastroenteritis.  Outbreaks in crowded settings (eg, schools, cruise ships, nursing homes) are common, and symptoms include vomiting and watery diarrhea.