Which statement best describes norovirus infectious dose and shedding in asymptomatic infections?

• A. High infectious dose and high shedding among asymptomatic infections
• B. High infectious dose and low shedding among asymptomatic infections
• C. Low infectious dose and low shedding among asymptomatic infections
• D. Low infectious dose and high shedding among asymptomatic infections

Answer: (D)

Norovirus is highly contagious because only a small amount of virus is needed to cause infection, and people without symptoms can still spread a lot of virus. The infectious dose is very low, so even minimal exposure can start an infection. At the same time, individuals who are asymptomatic can shed substantial quantities of virus in their stool, sometimes at levels comparable to those who are ill, and for a period after exposure. This combination — low infectious dose and high shedding in asymptomatic infections — explains why norovirus outbreaks can spread rapidly in settings like food service and daycare, even when people look and feel fine. The other statements don’t fit because norovirus doesn’t require a high dose to infect, and asymptomatic individuals aren’t typically characterized by consistently low shedding.