The stomach bug spreads mainly through the fecal-oral route, meaning tiny particles of an infected person’s stool or vomit get into your mouth. That can happen directly, through contaminated food or water, or by touching a surface where the virus is living. The most common culprit is norovirus, which is extraordinarily contagious. As few as 10 to 100 viral particles can cause an infection, and a single bout of vomiting releases billions of them.
Person-to-Person Contact
The most frequent way the stomach bug travels is directly between people. When someone with norovirus vomits, tiny droplets can spray through the air and land in another person’s mouth. Caring for a sick child, sharing utensils, or shaking hands with someone who didn’t wash thoroughly after using the bathroom are all common scenarios. Because the infectious dose is so remarkably low, even a trace amount of contamination that you can’t see or smell is enough to make you sick.
Contaminated Food and Water
Food becomes a vehicle for the virus in several ways. An infected person who handles food with bare hands can transfer the virus directly. Airborne droplets from nearby vomiting can settle onto uncovered food. Produce can also be contaminated at the source if it’s irrigated with water containing sewage runoff, and shellfish, particularly oysters, concentrate the virus when they filter contaminated water.
Cooking doesn’t automatically make food safe. Norovirus can survive temperatures as high as 145°F (63°C), which means quick steaming methods commonly used for shellfish won’t reliably kill it. Thorough cooking at higher temperatures is necessary, especially for oysters and other filter-feeding shellfish.
Drinking and recreational water can also carry the virus. A septic tank leaking into a well, someone vomiting or having diarrhea in a swimming pool, or inadequate chlorine treatment at a water facility can all lead to outbreaks.
Surfaces and Objects
Norovirus is remarkably durable outside the body. It can survive on hard surfaces like countertops, doorknobs, and plastic for more than two weeks. When someone with the virus touches a surface, or when microscopic vomit droplets land on it, that surface becomes a reservoir. You pick up the virus on your fingers, then touch your mouth or prepare food, and the cycle continues. This is why outbreaks tear through cruise ships, daycare centers, and nursing homes so efficiently: high-touch surfaces in shared spaces create endless opportunities for transfer.
Who Spreads It, and for How Long
People are most contagious while they have symptoms and for at least 48 hours after vomiting and diarrhea stop. That 48-hour window is important. The CDC recommends staying home from work, school, or food preparation for a minimum of 48 hours after your last symptoms resolve. Some local health regulations require even longer.
What makes containment harder is that not everyone who carries the virus gets sick. A meta-analysis published in The Lancet estimated that roughly 7 to 9 percent of infected people show no symptoms at all. During outbreaks, that figure climbs to around 18 percent. Among food handlers specifically, about 3 percent may carry the virus asymptomatically. These silent carriers can still shed the virus and contaminate surfaces and food without ever realizing they’re infected.
Why Alcohol-Based Hand Sanitizer Falls Short
Norovirus is a non-enveloped virus, which means it lacks the fatty outer coating that alcohol-based sanitizers are designed to dissolve. In lab testing, washing hands with soap and water for 30 seconds removed norovirus particles completely from finger pads. Alcohol-based hand disinfectants showed inconsistent results, sometimes achieving little to no reduction at all. If you’re dealing with a stomach bug in your household, soap and water is the go-to for hand hygiene, not the pump bottle of sanitizer on the counter.
How to Clean Contaminated Surfaces
Standard household cleaners won’t reliably kill norovirus. Chlorine bleach is the recommended disinfectant, but the concentration matters depending on the situation:
- Items that touch food or mouths (dishes, toys): 1 tablespoon of bleach per gallon of water
- Most hard surfaces (counters, doorknobs, toilets): 1/3 cup of bleach per gallon of water
- Heavily contaminated areas (where vomit or diarrhea made direct contact): 1 and 2/3 cups of bleach per gallon of water
The bleach solution needs to sit on the surface for 10 to 20 minutes before you rinse it off with clean water. Simply wiping a surface down and rinsing immediately won’t give the bleach enough contact time to inactivate the virus. When cleaning up vomit or stool, wear disposable gloves and clean the area outward from the edges to avoid spreading contamination further.
Why Outbreaks Happen So Fast
The combination of norovirus traits creates a near-perfect storm for rapid spread. The infectious dose is tiny. The virus survives on surfaces for weeks and resists both heat and alcohol sanitizers. Symptoms take 12 to 48 hours to appear after exposure, giving the virus a head start before anyone knows to take precautions. Vomiting aerosolizes the virus, contaminating surfaces and air in the immediate area. And a meaningful percentage of infected people never show symptoms but still shed the virus. In close quarters like a household, school, or shared office, all of these factors stack, which is why a single case often becomes dozens within days.