What You Need to Know About Foodborne Illnesses This Summer


By Mimi Cameron, MD

One of the great joys of summer is eating outdoors: at picnics, ballgames, street fairs, sidewalk cafes, or in your own backyard. But summer is also a time to be careful about food poisoning, especially when food sits outdoors in high temperatures. An estimated 48 million people get sick each year from foodborne illnesses, according to the Centers for Disease Control and Prevention (CDC), and those numbers peak during the summer months.

Scientists have identified more than 250 foodborne diseases, mostly infections caused by bacteria, viruses, or parasites, but also some toxins and chemicals. These are the top five, according to the CDC:

  • Norovirus is by far the most common, causing diarrhea, vomiting, nausea, and stomach pain, and sometimes fever, headache, and body aches. It develops within 12 to 48 hours of exposure and usually resolves within one to three days. Some commonly contaminated foods are leafy greens, fresh fruits, and shellfish grown in contaminated water.
  • Salmonella can cause diarrhea, fever, and abdominal cramps within 12 to 72 hours of infection and usually lasts four to seven days. Outbreaks have been linked to everything from canned tahini and precut melon to frozen raw tuna.
  • Clostridium perfringens is a bacterium commonly found on raw meat and poultry. Outbreaks are associated with foods prepared in large quantities and kept warm for a long time before serving. Diarrhea and abdominal cramps develop within six to 24 hours of exposure and usually last only 24 hours.
  • Campylobacter causes diarrhea (often bloody), fever, and abdominal cramps, and sometimes nausea and vomiting, symptoms that develop two to five days after exposure and usually resolve within a week. It is associated with contaminated food preparation areas and ingesting unwashed produce, undercooked meat, and raw or unpasteurized dairy products.
  • Staphylococcal food poisoning comes on very suddenly, within 30 minutes to eight hours of infection, and is usually caused by not washing your hands before handling food. Staph bacteria multiply in the food and produce a toxin that causes the symptoms.

Like most foodborne illnesses, these usually resolve on their own. Be careful to stay hydrated; dehydration can cause serious complications. You should consult your doctor if symptoms are severe or persistent (including bloody diarrhea, a fever over 100 degrees F, and weakness or other signs of dehydration), or if the patient is very young, very old, pregnant, or has a compromised immune system. Your doctor will review your symptoms and, if necessary, take a stool or blood sample.

Though most foodborne illnesses don’t require treatment, some (including some parasites) do require medical intervention. There are also some relatively rare foodborne illnesses that need to be treated immediately. Here are a few:

Botulism is associated with improperly canned or fermented foods, and symptoms usually begin with weakness of muscles of the face and throat and can even affect breathing and spread to other parts of the body. It requires an immediate trip to the emergency room.

Listeria is a potentially life-threatening infection that must be treated with antibiotics. Usually caused by foods that are contaminated during processing, like deli meats and cheeses, it can cause severe complications, including gastroenteritis and invasive meningitis. Most people report symptoms within one to four weeks of eating contaminated food.

E. coli bacteria live in your intestines and are mostly harmless, but some strains, including enterohemorrhagic E. coli, can cause severe bloody diarrhea. Recent outbreaks have involved ground beef, leafy greens, sprouts, flour, and other contaminated foods.

Preventing Foodborne Diseases

The single most important way to prevent infectious disease is to wash your hands. Use soap and running water and scrub thoroughly for at least 20 seconds (approximately the time it takes to sing “Happy Birthday” twice). Wash before and after preparing food; before eating; and after handling garbage, touching pets or pet food, changing diapers, using the toilet; and after coughing, sneezing, or blowing your nose. If you don’t have access to soap and water, your second-best option is a hand-sanitizer containing at least 60 percent alcohol.

  • You should also wash fruits and vegetables (with the exception of prewashed lettuce) before eating or cooking. You don’t need special chemicals or soap. Running water is sufficient.
  • Clean your cooking tools and work areas with soap and hot water. And never cross-contaminate raw animal products and other foods. Use separate utensils and cutting boards for raw chicken, beef, fish, and eggs. And, if possible, clean all utensils in the dishwasher after using them.
  • If you are cooking something that calls for raw eggs (such as homemade mayonnaise, chocolate mousse, or tiramisu), use pasteurized eggs, which are sold as liquid egg products or pasteurized in the shell. And don’t offer raw eggs or fish (including sushi, poke, and ceviche) to pregnant women, babies, the elderly, or anyone whose immune system is compromised. Unpasteurized dairy products, including unpasteurized soft cheeses, should also be avoided by anyone in these groups.
  • All perishable food should be refrigerated at 40 degrees or colder. Be aware of how long it is safe to keep foods in the fridge: no more than a couple of days for raw meat, and three or four days for leftovers. And food should not be left out of the refrigerator for more than two hours (one hour if the temperature is 90 degrees F or above). Frozen foods should be thawed in the refrigerator or in the microwave, not on the counter.
  • Always cook meat and fish to a safe temperature. The only way to be sure is to use a food thermometer and consult cooking charts that usually come with the thermometer, or are readily available online.

It’s important to remember that most people easily recover from foodborne illnesses. But taking simple precautions should allow you to enjoy a happy, healthy summer of carefree al fresco dining.

To learn more about safely storing foods, visit the U.S. Department of Agriculture website.

Miriam L. Cameron, MD, is a board-certified infectious disease specialist and internist with Mid-Atlantic Permanente Medical Group. She sees patients at the Kaiser Permanente Gaithersburg Medical Center.

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