Norovirus starts suddenly. Unlike many infections that build gradually, norovirus typically goes from nothing to intense nausea and vomiting within a narrow window of 12 to 48 hours after exposure. Most people don’t experience a slow buildup of warning signs. Instead, the illness hits fast, often catching people off guard in the middle of the night or during a normal day.
How You Catch It
Norovirus spreads through the fecal-oral route, which sounds straightforward but plays out in ways most people don’t expect. The obvious path is touching a contaminated surface and then touching your mouth, but the virus also travels through the air. When someone with norovirus vomits, the act itself launches viral particles into the surrounding air as fine droplets. One study in a hotel restaurant found that the risk of infection among diners was directly tied to how far they sat from the spot where someone vomited. The closer you were, the higher your chances.
The virus is also remarkably efficient at making you sick. As few as 18 viral particles can trigger an infection, which is an almost impossibly small amount compared to most pathogens. An infected person’s vomit and stool contain enormous quantities of virus, so even a tiny trace of contamination on a doorknob, countertop, or shared food is enough to start a new infection. You can also catch it from contaminated water or food, particularly raw shellfish or produce handled by someone who’s infected.
What Happens Inside Your Body
Once swallowed, the virus targets the lining of your small intestine. It attaches to cells using specific sugar molecules on their surface called histo-blood group antigens, the same molecules that determine your blood type. This is why some people seem more susceptible than others. People with certain blood types (particularly type O and type A who are “secretor positive,” meaning they express these sugar molecules in their saliva and gut lining) appear to have a lower threshold for infection.
The virus hijacks intestinal cells to replicate, triggering inflammation that disrupts your gut’s ability to absorb water and nutrients. This is what produces the watery diarrhea. The nausea and vomiting are driven by signals sent to your brain as your immune system detects the invasion. All of this unfolds quickly because the virus replicates fast and your body mounts an aggressive response.
The First Symptoms
The earliest sign is usually nausea, which can appear abruptly and escalate within minutes. From there, the full picture develops rapidly:
- Nausea and vomiting, often intense and repeated
- Stomach cramps or abdominal pain
- Watery diarrhea
- Low-grade fever
- Muscle aches and general malaise
There’s no real prodromal phase with norovirus, no days of feeling “a little off” beforehand. Research on viral shedding confirms this: the virus doesn’t appear in stool until symptoms begin, meaning the onset of shedding and the onset of illness happen almost simultaneously. Viral shedding in stool begins around 0.8 to 1.4 days after exposure and peaks at roughly 1.5 to 2.3 days, closely tracking symptom onset. The acute illness usually lasts one to three days.
When You’re Contagious
You become contagious as soon as symptoms start, and you stay contagious for some time after you feel better. The virus continues to shed in your stool even after vomiting and diarrhea stop. This is a major reason norovirus spreads so effectively in households, cruise ships, and schools. People return to normal activities feeling recovered, but they’re still capable of passing the virus to others through inadequate hand hygiene or shared spaces.
Why It Spreads So Easily in Winter
Norovirus is sometimes called the “winter vomiting bug,” and several factors converge to make colder months its peak season. The virus survives longer on surfaces and in water at lower temperatures. Low humidity, common in heated indoor environments during winter, also improves the virus’s ability to persist outside a host. Norovirus particles can remain infectious on surfaces for up to two weeks and in water for more than two months.
Behavior matters too. Cold weather pushes people indoors into closer contact. The school year is in full swing, and holidays like Thanksgiving, Christmas, and New Year’s create large indoor gatherings that give the virus ideal conditions to jump between people. The combination of a hardier virus and more human-to-human contact creates the seasonal spikes seen every year.
Cleaning Up After Exposure
Standard hand sanitizer does not kill norovirus reliably. Washing your hands thoroughly with soap and water is far more effective. For surfaces, you need a bleach solution strong enough to destroy the virus: the CDC recommends 5 to 25 tablespoons of household bleach (the standard 5% to 8% concentration) per gallon of water. You can also use a disinfectant that’s EPA-registered specifically against norovirus, since many common household disinfectants aren’t potent enough.
If someone in your home vomits, clean the area immediately and extend your cleaning radius well beyond the visible mess. Given that aerosolized particles from vomiting can travel across a room, wiping down nearby surfaces is worth the effort. Launder any contaminated clothing or linens on the hottest setting available, and avoid preparing food for others until at least two days after your symptoms resolve.