In most cases of food poisoning, a microbe in something you ate (or a pathogen that goes from your hand to your mouth) irritates your stomach and intestines—and the consequences aren't pretty, with symptoms that range from a mildly upset tummy to vomiting and bloody diarrhea. Even though the United States has one of the safest food supplies in the world, one in six people suffer foodborne illness every year, according to government estimates.

Read on to learn about some of the most common bugs that might be lurking in your lunch.

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How do you treat food poisoning?
As long as you're otherwise healthy, most cases of gastroenteritis (inflammation in the intestines caused by a virus, bacteria, or parasites) don't require treatment. Your body will (eventually) expel the bugs that are making you sick. There's not much you can do aside from rest and sip plenty of fluids. (Electrolyte-rich liquids like broth and coconut water are best.) You may be tempted to pop an OTC anti-diarrhea product, but ask your MD first; it may interfere with the natural healing process. Once you're keeping fluids down, slowly reintroduce solids, starting with bland, low-fiber food like the BRAT diet (bananas, rice, applesauce, and toast).

In more serious cases, you may want to get checked out by a doctor. Watch for any of these signs that warrant medical attention: Diarrhea with a fever above 101 degrees F; dizziness, lightheadedness, or intense thirst; an inability to keep anything down for 24 hours; diarrhea that lasts for five days or more.

Norovirus
Norovirus is the pathogen responsible for outbreaks of vomiting and diarrhea on cruise ships, but a 2014 Centers for Disease Control and Prevention (CDC) report found that you're far more likely to pick up the bug in a restaurant or cafeteria. Norovirus is the most common cause of gastroenteritis in the U.S., infecting more than 19 million people a year.

What you need to know: It's highly contagious: The number of virus particles that fit on the head of a pin would be enough to make more than 1,000 people sick. Symptoms should resolve within 60 hours, but you may continue to spread the pathogen for two weeks or more.

How to avoid it: Wash fruits and veggies well, and cook shellfish thoroughly. (Norovirus can survive temps as high as 140 degrees.) And be sure to wash your hands (like, really wash them). You can also get the pathogen from contact with an infected person, or by touching a contaminated surface.

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Salmonella
Batter-covered spoon lickers, beware: the strain of Salmonella that causes most illnesses today infects the ovaries of hens, which then lay contaminated eggs. The bacteria are also found in as many as one in eight chickens raised for meat, according to the USDA. Each year, Salmonella causes four to seven days of misery (including cramps, diarrhea, and fever) for approximately 1.2 million Americans.

What you need to know: Salmonella can also contaminate other types of meat and seafood, cheese, unpasteurized milk and juice, and raw produce.

How to avoid it: Say no to sunny-side-up and soft-boiled eggs. Eggs with firm yolks and whites are safest to eat. Heat your poultry to 165 degrees, and ground beef to 160 degrees.

Botulism
Spores of C. botulinum produce a neurotoxin that causes botulism—a rare but severe type of food poisoning that can lead to respiratory failure and death. Most of the 10 to 30 outbreaks of botulism reported each year can be traced to home-canned foods, according to the FDA.

What you need to know: Classic symptoms include double vision, slurred speech, difficulty swallowing, and muscle weakness. If you think you might have botulism, seek medical help immediately. Prompt treatment with an antitoxin can block the effects of the poison.

How to avoid it: The Mayo Clinic recommends boiling home-canned foods for 10 minutes before you eat them. Other tips: Eat baked potatoes wrapped in foil while they're still hot (not at room temperature), and store oils infused with garlic or herbs in the fridge.

E. coli
E. coli naturally live inside humans and animals, and for the most part, the bacteria are harmless. But a few strains—including the notorious O157:H7— can wreak havoc on the lining of your small intestine when ingested. Expect bloody diarrhea, plus vomiting and severe stomach cramps.

What you need to know: Runoff from cattle farms can spread E. colito produce grown in nearby fields. Spinach and lettuce are especially susceptible to contamination.

How to avoid it: A 2015 report that examined 1,000 E. coli cases found that 80 percent were linked to vegetables or beef. Ground beef is a common source of infection because it contains meat from many cows—so order your burgers medium or well-done.

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Campylobacter
Responsible for an estimated 1.3 million cases of campylobacteriosis a year, this pathogen can come from unpasteurized dairy products (if a cow had a Campylobacter infection in her udder, for example). But most cases are linked to raw or undercooked meat or poultry. The good news: Symptoms usually resolve on their own. The bad news: The diarrhea, cramping, and fever last about a week.

What you need to know: Even one drop of juice from contaminated raw chicken meat can make you sick.

How to avoid it: While you're cooking, use a separate cutting board for raw meat to avoid cross-contaminating veggies and other foods. And don't skimp on the cleanup: Scrub the cutting board, countertops, and utensils with soap and hot water.

Listeria
Pregnant women worry about this foodborne pathogen. It can cause listeriosis, which may lead to miscarriage or a serious illness for the newborn. But anyone with a weakened immune system is at higher risk for the infection, with symptoms ranging from a stiff neck to convulsions and loss of balance. An estimated 1,600 cases occur in this country annually.

What you need to know: Although pasteurization and high temperatures kill Listeria, cold cuts and deli meats are a common source of the bacteria because contamination may occur at the deli counter, or in the factory (after cooking but before packaging).

How to avoid it: According to the CDC, people at higher risk should skip ready-to-eat meats, unless they're heated to steaming hot before serving. Other foods on the avoid list: Refrigerated pate or meat spreads from a deli counter, soft cheese made with unpasteurized milk, and refrigerated smoked seafood (like lox).

Staph
Many people have Staphylococcus aureus all over their skin, and the bacteria typically doesn't cause any issues. Until, that is, it gets in our food. As the bugs multiply, they produce toxins that quickly trigger the classic symptoms of food poisoning—sometimes as soon as an hour later.

What you need to know: Handmade foods that don't require further cooking are the likeliest suspects: Think prepared salads (from macaroni to tuna), sandwiches, and cream-filled bakery desserts.

How to avoid it: Practice good hand hygiene. Stay away from the kitchen when you have a nose or eye infection, or wounds or skin infections on your hands or wrists.

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Clostridium perfringens
C. perfringens may live in your intestine without doing any harm. But when you ingest large numbers of the toxin-producing bacteria, cramps and diarrhea strike with a vengeance for up to 24 hours.

What you need to know: C. perfringens is one of the most frequent causes of food poisoningin the U.S. Outbreaks often occur in cafeterias and at catered events, because the bacteria's spores can germinate in food that's cooled or warmed at temperatures between 54 and 140 degrees F for long periods of time.

How to avoid it: To destroy C. perfringens on food that's been sitting out or stored as leftovers, reheat it to 165 degrees F.

Shigella
Disgusting but true: This highly contagious group of bacteria is spread through stool. You can pick up the bug in food contaminated by an infected person, or on produce grown in a field that contains (yikes) human sewage. The result: GI distress and tenesmus, the painful sensation of needing to go number-two even when your bowels are empty.

What you need to know: Shigella is a common cause of traveler's diarrhea (a.k.a. Montezuma's revenge and Delhi belly). Although it usually goes away on its own in five to seven days, docs often prescribe antibiotics for mild cases to speed the process. Now, drug-resistant shigellosis is on the rise in the U.S.

How to avoid it: When traveling in a developing country, order carefully. Steaming hot foods are generally safe, for example, and drinks that come in sealed containers. You can also download the CDC's "Can I Eat This?"app, which has info tailored to different countries.

Bacillus cereus
This nasty little bug causes not one, but two kinds of food poisoning: A type associated with diarrhea and another with vomiting. Fortunately, both only last for about 24 hours. In the meantime, try to stay hydrated.

What you need to know: Rice that's been sitting at room temperature is generally implicated in vomiting-type outbreaks. But the bacteria are found on a wide variety of foods and multiple rapidly at room temperature.

How to avoid it: Be careful not to let leftovers sit out for too long. Store them in the fridge in wide, shallow containers ASAP. Prepping ahead of a meal? If it's more than two hours 'til chow time, keep cold items at 40 degrees or below, and keep hot foods at a minimum temp of 140.

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Toxoplasma gondii
You might recognize this microbe as the reason pregnant women are told to stay away from cats' litter boxes. But the single-celled parasite is also spread in undercooked, contaminated meat—especially pork, lamb, and venison. Most people who've picked up the bug (the CDC estimates 60 million people in the U.S.) don't even know they have it. But in anyone with compromised immunity, it can cause the disease toxoplasmosis.

What you need to know: Symptoms of toxoplasmosis vary widely: Some people might think they have the flu for a month or more, while severe cases can cause brain damage.

How to avoid it: There's not much you can do aside from following general food safety protocol.

Vibrio parahaemolyticus
Found in brackish waters, estuaries, and coastal bays, this bacterium thrives during the warm, summer months and is known tocontaminate shellfish. Infection with V. parahaemolyticus is no fun. Watery diarrhea, cramps, vomiting, fever—you get the picture. These symptoms typically last up to three days.

What you need to know: Raw oysters are the usual culprit.

How to avoid it: Steer clear of the raw bar if you're worried about getting sick. Cooking shellfish at home? Boil osyters, clams, and mussels for five minutes after the shells open, or steam until the shells open. (Toss any that don't.) Boil shucked oysters for a minimum of three minutes, or fry in oil at 375 degrees for at least three minutes.

This article originally appeared on Health.com.