Is Food Poisoning Contagious From Person to Person?
So, you grabbed dinner from a dubious location and now your spouse or kid or roommate is curled over the toilet puking their guts out. Clearly, their food choice was riskier than yours, but now you're wondering: "Can I catch this from them? Is food poisoning contagious?"
If it's that kind of frantic googling that brought you here, the answer is "sometimes" and you can cut to the section that says "What Kinds."
If you're here for less imminent reasons, then let's first talk about why the better question is actually "can food poisoning be contagious?"
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What is Food Poisoning?
Funny enough, the colloquial understanding of "food poisoning" is a lot more straightforward than professional attempts to define it. That's because laymen characterize food poisoning by a set of symptoms caused by a whole bunch of different things.
When most people think of food poisoning, they picture a period of acute sickness after eating "bad" food. Almost always, the symptoms you're imagining are gastrointestinal: vomiting, diarrhea, stomach cramps, and the like.
Sometimes, illnesses we categorize as food poisoning only include GI symptoms sometimes – that's the case with botulism. Botulism's main symptoms are muscle weakness and paralysis, but it comes from eating contaminated food and it sometimes includes vomiting and diarrhea.
When you ask medical or public health professionals, you'll get definitions that don't line up with the general understanding.
For example, the USDA defines food poisoning very narrowly. They say it's a form of foodborne illness caused by the ingestion of "pre-formed toxins." Their definition restricts food poisoning to illnesses like botulism, many types of seafood poisoning, and eating poisonous mushrooms. It excludes one of the most common illnesses that people call food poisoning: norovirus.
Other medical sources, like the Mayo Clinic, define food poisoning as any foodborne illness. This covers most of the bases, but it includes illnesses that people don't usually think of as food poisoning, like tapeworm.
Food poisoning is a layman's term, so we'll use the layman's definition.
What Causes Food Poisoning?
Foodborne illness is a big category with a lot of potential causes. Food poisoning, by the layman's definition, is a smaller category, but it's still pretty broad.
Food poisoning can be caused by pathogens, bacteria, viruses, parasites, and fungi. They can cause illness directly, or they can produce toxins that make you sick.
In other cases, the food you're eating contains toxins by itself. A lot of seafood poisoning is the result of your meal ingesting toxins while it was alive. In other cases, the meal itself makes the toxin – this is the case in pufferfish (or fugu) poisoning.
Finally, food poisoning can happen if your food is contaminated with chemicals.
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Is Food Poisoning Contagious?
Each source of food poisoning has its own quirks, so when you ask, "is food poisoning contagious," the answer is always, "it depends on what kind."
Food poisoning that's caused by a pathogen is infectious, but not necessarily contagious from human to human. Many foodborne pathogens come to us via animals, instead.
Sometimes the pathogens or toxins started out inside the animal you're eating – we've already mentioned toxins in seafood. Most vertebrates have E. coli and Salmonella in their intestines, so cross-contamination happens during the butchering process. In other cases, the pathogens could be introduced through animal feces, whether it's the result of animal activity in the fields where your greens were grown or pests in the factory where your food was processed.
In many cases, you can tell something is "food poisoning" because everyone who ate the same thing gets ill at or near the same time. It won't always be contagious.
Some kinds of food poisoning can't be passed from person to person.
Food poisoning caused by toxins or chemicals can only be gotten by eating contaminated food. Botulism can't be passed from person to person, and most shellfish poisoning is toxin-based and therefore not contagious.
Some living pathogens that cause food poisoning have a life cycle that makes person-to-person transmission impossible. Trichinosis is caused by a worm that can only make you sick when you consume muscle tissue like undercooked pork riddled with larvae.
For other pathogens, person-to-person transmission is possible but rare because the organism can't live in the environment for long. When that's the case, food safety measures and good hygiene make it hard for the pathogen to make the jump.
What Kinds of Food Poisoning Can Be Contagious From Person to Person?
Person-to-person transmission of food poisoning typically requires "fecal-oral transmission" (thanks a lot, epidemiologists).
It's typically not (thank goodness) from direct contact between those orifices. Usually, it passes by way of someone's hands or some other object.
The heavyweight champion of contagious food poisoning is norovirus, sometimes referred to as "the stomach flu."
It's incredibly infectious – sick people shed billions of norovirus particles and it doesn't take much to pass it on. You can infect 1,000 people with the amount that fits on the head of a pin. The symptoms also come on very suddenly, which means you can infect a lot of people before you realize you need to stay home.
It's also hard to kill – it can survive temperatures as low as -112°F and as high as 145°F. It can live on countertops and cooking utensils for up to 2 weeks, and it's resistant to ordinary sanitation measures like soap and hand sanitizer.
Put all that together and it's no surprise that norovirus accounts for 58% of foodborne illness outbreaks every year, according to the CDC, and that 70% of reported outbreaks are caused by food service workers handling food while contagious.
Hepatitis A is another highly contagious foodborne infection. People with Hepatitis A experience liver and GI symptoms.
The good news is that, unlike Hepatitis B and C, Hepatitis A usually doesn't become chronic. The bad news is, for a "short-term" infection, it can drag on for a while. Symptoms appear 2 to 7 weeks after infection and typically last for less than 2 months (but some people can be sick for 6 months).
People are the most contagious soon after they're infected, when they may not even know they are. Healthy adults are contagious for up to 2 weeks after symptoms begin, but people with weaker immune systems may be contagious for six months.
Luckily, there is a vaccine. If you know you're at risk for exposure to Hepatitis A or if you think you've been exposed, getting the vaccine can prevent infection. Post-exposure vaccination has to happen within 2 weeks of exposure, though – for most people, this is before symptoms appear.
Several other foodborne pathogens are contagious from person to person. Along with norovirus and Hepatitis A, salmonella, shigella, and E. coli are the most common culprits. Typically, health departments require food workers to report those five illnesses to their manager and stop handling food.
Other pathogens that cause food poisoning are contagious but less common, like rotavirus and Giardia lamblia.
How Can You Prevent Contagious Food Poisoning?
The best way to prevent food poisoning of all kinds is to follow food safety protocols, avoid restaurants with poor food safety ratings, and insist that your government enforces strict regulations on the food supply. Take extra precautions during power outages, boil water notices, and other situations where normal safety measures lapse.
If someone close to you gets food poisoning, you probably won't know the exact cause. You should assume it's contagious just to be on the safe side. You can usually keep yourself safe with good hygiene – wash your hands frequently with soap and water for 20 seconds, keep your hands away from your face, and sanitize the surfaces that the person with food poisoning touches. The infected person should also practice frequent handwashing.
Statistically, it's probably norovirus, in which case your loved one is contagious for 3-5 days. Keep up cleaning and hygiene precautions for at least that long. Other sources can only survive in the environment for a couple hours, but people can be infectious for several weeks so you may want to limit direct contact, even if you step down your cleaning routine.
If the sick person has jaundice or learns they've been exposed to Hepatitis A, seek the vaccine immediately.
Preventing contagious foodborne illness from outside your intimate circle is tougher. Despite official recommendations, 51% of food service workers admit that they work when they should stay home. They're afraid of getting fired or can't live without the money from that shift. There aren't easy answers to change that pattern – it would require widespread industry change.
Rigorous food safety compliance can help reduce the likelihood of contagious food poisoning, however. Following Time and Temperature Control guidelines, training and enforcing best food handler practices, and requiring food safety manager certification are all steps to ensuring that food is as safe from food poisoning as it can be.