Your Questions About Norovirus, Answered

Symptoms begin 12 to 48 hours after exposure and are sudden: diarrhea, vomiting, nausea, and stomach pain are the most common, with fever, headache, and body aches as "other symptoms" (CDC). Most people are better in 1 to 3 days. Roughly one in three infected adults in challenge studies never developed symptoms at all — but shed virus regardless.

The complication is dehydration. The CDC's warning signs are decreased urination, dry mouth and throat, feeling dizzy when standing, and — in children — crying with few or no tears and unusual sleepiness or fussiness. Severe dehydration "may require hospitalization for treatment with fluids given through your vein."

The age pattern is the most useful fact on the Symptoms page: the emergency-department visits are "mostly in young children," while the deaths are "mostly among adults aged 65 and older" (CDC). By age five, one child in 40 will have had an ED visit for norovirus and one in 160 a hospitalization.

Read the full Symptoms page — timeline, who is hospitalized, dehydration grading, and why there is no published fatality rate →

Care is supportive, and for most people that means fluids at home. The CDC's advice: "oral rehydration fluids that you can get over the counter are most helpful for mild dehydration"; sports drinks and other caffeine-free, alcohol-free drinks "can help" but "may not replace important nutrients and minerals." WHO describes oral rehydration solution as "a mixture of clean water, salt and sugar" that "costs a few cents per treatment." Severe dehydration means IV fluids in hospital.

What "supportive care" adds up to across a US year, per CDC: about 2.27 million outpatient visits, 465,000 emergency-department visits, and 109,000 hospitalizations — nearly all of the last for dehydration. Set against 19–21 million illnesses, roughly six in seven are managed at home without a clinician. No antiviral is approved; the most advanced vaccine candidate is in a Phase 3 trial of nearly 38,000 adults with results expected in 2027.

Read the full Treatment page — rehydration when vomiting, symptom management, returning to eating, and when to seek care →

None of the US figures on this page is a count. Norovirus is not individually reportable — CDC's reporting page states that health departments "are not required to report individual cases of norovirus illness to CDC," and most clinics do not test for it. The 19–21 million illnesses trace to Hall et al. (2013); the 109,000 hospitalizations, 465,000 ED visits, and 900 deaths to Burke et al. (2021), whose confidence intervals — 80,000–145,000 hospitalizations, 650–1,100 deaths — the CDC page leaves out. The 685 million global illnesses is a model with an uncertainty range of 491 million to 1.1 billion.

That is why this site does not publish a norovirus case-fatality rate or hospitalization rate: dividing one modeled estimate by another produces a decimal that looks precise and is not. The Norovirus Risk Perspective page shows each figure beside its source and date, leaves those two cells blank with the reason, and links to the hub's Virus Risk Perspective, where norovirus — the highest-incidence, among the lowest-lethality viruses in the set — is compared with 14 others on the same five measures.

When this site gets something wrong, or is told it has and turns out not to have, the corrections page records it: what was published, what it says now, and the source that settled it.