An overhead shot of a table laden with food.

During the recent outbreak of E. coli in romaine lettuce, the Centers for Disease Control and Prevention (CDC) issued an update that contained a curious piece of information. Some of the victims had not eaten tainted romaine lettuce; they had simply been in contact with people who had.

Though it may seem surprising, getting a case of food poisoning from a person instead of food isn’t all that unusual.

“This is a very common occurrence with foodborne-illness outbreaks,” says James Johnson, M.D., an infectious disease specialist and a professor of medicine at the University of Minnesota. “There are almost always secondary incidents of sick people passing the virus to people around them.”

How You Can 'Catch' Food Poisoning

People get sick when bacteria, such as salmonella and E. coli, contaminate the food they eat.

This can happen in a variety of ways. Bacteria live in the intestines of cattle, chickens, and other animals raised for food. If feces come into contact with the meat during slaughter, that meat can carry the bacteria. For plant foods, the source is typically animal waste from the field (such as in the form of manure) or tainted water. The bacteria can also be spread through cross-contamination in the processing plant or in a home or restaurant kitchen.

More on Food-Poisoning Precautions

Fecal contamination is also how foodborne bacteria are transmitted secondarily from person to person. Diarrhea is a symptom of almost all foodborne illness, creating many opportunities for dirty hands.

“When a sick person transmits E. coli or salmonella to someone around them, it’s usually a case of not washing their hands properly after using the bathroom,” says Sana Mujahid, Ph.D., manager of food-safety research at Consumer Reports.

Though unpleasant to envision, bacteria generally spread via the “fecal-oral route,” which is when trace amounts from one person’s feces end up in someone else’s mouth. Those poorly washed hands can contaminate a host of objects and surfaces, including light switches, doorknobs, and kitchen surfaces.

Norovirus, another foodborne pathogen, is transmitted particularly easily from person to person in close quarters. Outbreaks often begin when an infected food handler contaminates a batch of food, then people either eat the food or pass the virus to others in close physical proximity (say, on a cruise ship or at a church potluck).

“Norovirus is famous for causing outbreaks at a particular event, time, and geographic cluster,” says Johnson.

How to Stay Safe

Even trace amounts of contaminated feces can pass foodborne bacteria from one person to another. Johnson says you’re very rarely going to see visible evidence of contamination.

Proper hygiene is always important, but it becomes even more so if you suspect you have food poisoning or you live with someone who does. To prevent transmitting bacteria yourself or picking them up from someone around you, follow these tips:

Wash hands (again and again). Thorough and rigorous hand-washing—using hot water and plain soap—is the most vital step you can take to keep foodborne pathogens from spreading person to person. Wash after using the bathroom, changing a diaper, taking care of someone who is ill, as well as before preparing food. Mujahid says you should follow the “ABC rule” of hand-washing: Wash for the length of time it takes to recite the alphabet.

Don’t rely on hand sanitizers. Johnson says it’s not a terrible idea to use an alcohol-based hand sanitizer because it can kill some of the germs, according to the CDC—but it won't kill all of them. Sanitizers are good in a pinch, but hand-washing with soap and water remains a better bet.

Clean dirty linens. While this can apply to more obvious items like soiled bed sheets, washcloths, and towels, Johnson notes that even something like a dirty sleeve can transmit foodborne bacteria. While you don’t need to make yourself crazy washing clothes every 5 minutes, err on the side of caution with any fabric that may have come into contact with feces.

Wipe down and sanitize. Disinfecting all common surfaces (e.g., kitchen counters, bathroom sinks, and doorknobs) may seem like a pain, but it can go a long way toward isolating an outbreak in your household, according to Mujahid. Use a bleach solution or other disinfectant to wipe down bathroom and kitchen surfaces thoroughly and frequently.

Stay out of the kitchen. If there is even a small chance you have contracted a foodborne illness, don’t prepare food for other people. If you must use your kitchen, be particularly vigilant about washing your hands and cleaning surfaces you touch.