1. How is the virus transmitted?

Fecal-oral contamination. Infectivity can last for as long as 2 days after resolution of symptoms. The virus particles are extremely hardy; their infectivity persists after exposure to acid, ether and heat (60o C for 30 min).

2. What is known about the pathogenesis of the infection?

The incubation period is 24-48 hours, and the mean duration of illness is 12-60 hours. Nausea is prominent, with vomiting, non-bloody diarrhea, and abdominal cramps occurring in most cases. These symptoms are experienced by all age groups, but diarrhea is relatively more prevalent among adults, whereas a higher proportion of children experience vomiting. From 25-50% of affected persons also report headache, fever chills, and myalgias. (It is not clear whether these systems are caused by a viremia or the production of interferon). Adults have died during illness caused by Norwalk-like viruses, presumably from electrolyte imbalance. Late sequelae have not been reported, but the elderly often report persistence of constitutional symptoms for up to several weeks.

3. If the student with these symptoms visited the doctor, would laboratory tests likely be ordered? What treatment would be recommended?

No laboratory tests. Symptomatic care (encourage fluids) would be administered as long as patient appeared generally well. If the patient appeared dehydrated, then rehydration IV or oral would be needed. Further workup would only be performed if the patient=s symptoms worsened or did not resolve in 1-2 days.

4. Is the student likely to have this infection again?

Studies of volunteers have documented the paradox that persons with the highest preexisting levels of Norwalk antibodies are at highest risk of developing symptomatic infection. Most persons' antibody levels against Norwalk virus rise after infection; these titers normally peak by the third week and persist until approximately the sixth week, after which they decline. Although preexisting antibody levels correlate with risk of symptomatic illness upon exposure to the virus, acutely elevated antibody levels appear to correlate with resistance to reinfection. The nature of resistance and susceptibility to the Norwalk-like agents is poorly understood.