You get the stomach bug by swallowing tiny particles of feces or vomit from someone who’s already infected. That sounds dramatic, but it happens far more easily than most people realize. The virus responsible for most stomach bugs, norovirus, is so contagious that as few as 18 viral particles can make you sick. For perspective, a single infected person sheds billions of them.
The “stomach bug” (also called the stomach flu, though it has nothing to do with influenza) is actually viral gastroenteritis, an inflammation of the stomach and intestines. Norovirus is the most common cause in adults and children alike, while rotavirus is the leading cause in young children worldwide. Here’s how these viruses actually reach you.
Direct Contact With a Sick Person
The most straightforward route is person-to-person spread. If someone in your household, office, or school has the stomach bug, you’re at risk every time you share a space with them. Caring for a sick child, cleaning up vomit, or even just being nearby when someone gets sick can expose you. When a person vomits, tiny droplets spray into the air and can land in your mouth or on nearby surfaces and food. This is one reason the virus tears through families so quickly once one person comes down with it.
Contaminated Surfaces
Norovirus is remarkably tough outside the body. On hard surfaces like countertops, doorknobs, and light switches, the virus can survive for more than two weeks. Even on soft surfaces like carpet or fabric, it stays viable for days to a week. An infected person who doesn’t wash their hands properly (or at all) leaves invisible viral particles on everything they touch: handrails, elevator buttons, shared utensils, bathroom faucets, refrigerator handles.
You then pick up the virus on your fingers and transfer it to your mouth without thinking about it. The average person touches their face dozens of times per hour, so contaminated surfaces are one of the most efficient ways the bug spreads in households, offices, and schools.
Food and Water
Norovirus is the leading cause of foodborne illness outbreaks in the United States, responsible for roughly 50% of all food-related illness outbreaks. The foods most commonly involved are leafy greens like lettuce, fresh fruits, and shellfish, particularly oysters.
There are two main ways food gets contaminated. The first is at the source: oysters harvested from polluted water, or produce sprayed with contaminated water in the field. The second, and more frequent in restaurant outbreaks, is an infected food worker touching ready-to-eat foods with bare hands. Any food served raw or handled after cooking can carry the virus. This is why restaurant and catering outbreaks are so common, and why a single sick employee can trigger dozens of cases.
Why It Spreads So Fast in Certain Places
Cruise ships, daycares, college dormitories, and nursing homes are hotspots for stomach bug outbreaks. The common thread is large numbers of people sharing tight spaces, touching the same surfaces, and eating from communal food sources. On a cruise ship, passengers mix constantly in dining rooms, buffet lines, pool areas, and elevators. One person with unwashed hands touching the buffet serving spoon can start a shipwide outbreak. The same dynamic plays out in schools and childcare centers, where young children put contaminated fingers and objects in their mouths throughout the day.
From Exposure to Symptoms
After you’re exposed, symptoms typically appear within 12 to 48 hours. The onset is often sudden: you might feel fine one moment and violently ill the next. Vomiting, diarrhea, nausea, and stomach cramps are the hallmarks. Most people recover within one to three days, but you remain contagious even after you feel better. Viral shedding continues for days after symptoms resolve, which is why returning to work or school too soon can keep an outbreak going.
Why Hand Sanitizer Isn’t Enough
Alcohol-based hand sanitizers are not very effective against norovirus. Research comparing the two approaches found that washing hands with soap and water for 30 seconds completely removed norovirus particles from skin, while alcohol-based disinfectants showed inconsistent and significantly lower reductions. Soap and water physically wash viral particles off your hands, whereas alcohol struggles to inactivate this particular virus. Hand sanitizer is better than nothing when you’re out and can’t reach a sink, but it’s not a reliable substitute.
Cleaning Surfaces That May Be Contaminated
Standard household cleaners won’t reliably kill norovirus. You need a bleach-based solution, and the concentration matters. For most hard, nonporous surfaces like countertops and bathroom fixtures, mix one-third cup of bleach into one gallon of water. For heavily contaminated areas (where vomit or diarrhea made direct contact), use a stronger solution of one and two-thirds cups per gallon. For items that might go in someone’s mouth, like children’s toys, a milder solution of one tablespoon per gallon is appropriate.
Whichever concentration you use, 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 with a damp cloth won’t do much. When cleaning up vomit or diarrhea, start by removing the visible mess with disposable towels, then apply the bleach solution to the entire surrounding area. Wash any contaminated clothing or linens on the hottest setting available.
Practical Ways to Lower Your Risk
The single most effective thing you can do is wash your hands thoroughly with soap and water, especially before eating, after using the bathroom, and after caring for someone who’s sick. Scrub for at least 20 to 30 seconds and make sure to get under your nails, where viral particles hide.
- When someone at home is sick: Isolate their bathroom if possible. Disinfect shared surfaces multiple times a day with a bleach solution. Don’t share towels, cups, or utensils. Wash their laundry separately.
- When preparing food: Wash fruits and vegetables thoroughly. Cook shellfish to a safe internal temperature, since raw oysters are a well-documented source of outbreaks.
- In shared spaces: Avoid touching your face after handling shared objects like handrails, elevator buttons, or doorknobs. Wash your hands before eating, even if you’re just snacking.
- After recovery: Continue careful hand hygiene for at least a few days after symptoms stop, since you’re still shedding virus during that window.