Food-borne illnesses, Part II: Personal protection

Published: April, 2010

Food-borne infections are getting a lot of attention these days, as they should. Each year, roughly 76 million Americans get sick from something they ate, about 350,000 end up in the hospital, and some 5,000 die from their infection.

Last month, Harvard Men's Health Watch explored the ways microbes can contaminate our food, how the body reacts, and why government and industry reforms are needed to reduce our risk of illness. They are important issues, but they won't provide much comfort when you next order a hamburger or even a salad. Fortunately, you can do things to protect yourself. The first step is to know the enemy.

Rounding up the suspects

Because so many different culprits cause similar symptoms, it's usually impossible for a doctor to finger the villain on the basis of clinical findings. And since you would have eaten the guilty food days before the illness kicked in, it's rare for you to offer much help.

It takes considerable detective work to make the diagnosis. In most cases, an individual doctor starts the process by sending his patient's stool specimen to the lab. Stool cultures take several days; when the lab eventually identifies the pathogen, the next step is to report the infection to local public health authorities. If enough cases are reported, the outbreak is turned over to epidemiological sleuths who carefully interview patients to see if there is a common dietary element that could explain all the cases. Whenever possible, they will also test any suspicious leftovers or uneaten food samples. Finally, they trace the tainted food back to its point of origin, looking for possible contamination at each step from farm to kitchen. At the same time, authorities recall the guilty product to prevent additional infections. It's a slow and tricky process, which is why a large salmonella outbreak in 2008 was mistakenly attributed to raw tomatoes until jalapeo peppers were identified as the true culprit.

Tips for travelers

Traveler's diarrhea, or "tourista," is a well-known hazard for visitors to developing countries where sanitation is flawed. Here are some tips to prevent intestinal infections:

  • Wash your hands with soap and water or an alcohol-based hand gel before you eat.

  • Avoid salads, uncooked vegetables, and unpasteurized milk and cheese.

  • Only eat fruit that you've washed in clean water and peeled yourself.

  • Do not eat undercooked or rare food. Eat cooked foods while they are still piping hot. Be especially wary of food from street vendors.

  • Avoid the water unless you have boiled it yourself; chemical disinfectants and water filters are available for use in special circumstances. Don't use ice made from untreated water. Don't use untreated water to brush your teeth. In general, unopened bottled or canned beverages are safe, as is coffee or tea made from boiled water.

  • Ask your doctor about taking along antibiotics in case prevention fails.

  • Above all, suspect everything.

A rogues' gallery

Over 200 different microbes can cause food-borne illnesses. Any one of them will be very important if you're its victim, but we'll focus here on the most common and dangerous perpetrators.

Escherichia coli. E. coli is one of the most common bacteria in the human colon. Although we get along quite nicely with our own E. coli (as long as they stay where they belong), four groups of "foreign" E. coli can cause food-borne illness.

1. ETEC group. These bacteria cause "traveler's diarrhea" in visitors to developing countries who do not take proper precautions (see box). The bacteria spread when human feces contaminates water or food. Watery diarrhea is the main symptom, often with cramps and sometimes with low-grade fever. The symptoms resolve on their own in two to four days, but antibiotics can shorten the symptoms. ETEC E. coli infections are very uncommon in countries with advanced sanitation.

2. EIEC group. Members of this group cause a more dramatic illness called bacillary dysentery. Symptoms include diarrhea with blood and mucus, vomiting, cramps, and fever. The symptoms resolve within a matter of days and do not require antibiotics. Because EIEC organisms spread through food contaminated with human feces, bacillary dysentery is very uncommon in the U.S.

3. EPEC group. These bacteria cause diarrhea in infants, but they're now uncommon in the U.S.

4. EHEC group. This is the biggie, the dangerous E. coli you hear about in American outbreaks. It's a serious problem because of the main representative of this group, the infamous O157:H7 strain. Like the other E. coli groups, these bacteria live in the intestines of animals, especially cattle. The infection can spread through contaminated beef, particularly undercooked hamburgers, and through unpasteurized milk and vegetables and fruits that have been tainted by cow manure. About 100,000 cases a year occur in the U.S. Outbreaks have been traced to many foods, ranging from hamburgers to unpasteurized apple juice, spinach, and sprouts. The diarrhea is watery at first but, in severe cases, soon becomes bloody; cramps are severe, but there is little or no fever. Most patients recover in five to 10 days, but as many as 5% to 15% develop the dreaded, sometimes lethal, hemolytic uremic syndrome (HUS). Children and the elderly are particularly vulnerable to HUS, which features kidney failure and low red blood cell and platelet counts. Scientists believe that antibiotics and anti-diarrhea medications increase the risk of HUS, so these drugs should not be given to patients with suspected E. coli diarrhea.

Salmonella. One strain of Salmonella causes typhoid fever, an extremely serious infection that spreads when feces from an infected person contaminate water or food. As a result of good sanitation and hygiene, typhoid fever has virtually disappeared from the U.S., but another group of Salmonella lives in the intestines of many animals, including poultry, swine, and cattle. Several million Salmonella cases occur in the U.S. each year and have been traced to contaminated peanuts, jalapeo peppers, eggs, chicken, beef, and other foods. The major symptoms are cramps and diarrhea, sometimes containing blood or mucus. Most patients recover in four to seven days; antibiotics are reserved for severe cases and for patients who are at risk for complications.

Campylobacter. E. coli and Salmonella get all the press, but Campylobacter is much more common, causing millions of cases of food-borne illness in the U.S. each year. The bacterium lives in the intestinal tract of most chickens, and it's also present in cattle and other animals. Undercooked poultry is the major source of infection; cramps, fever, and copious diarrhea, which sometimes contains blood, are the main symptoms. Most patients recover in seven to 10 days, but relapses can occur. Antibiotics can shorten the illness.

Listeria. Although food-borne infections with this bacterium are relatively uncommon, they can be serious. Unpasteurized milk, soft cheeses, and other dairy products are the foods most likely to be contaminated by Listeria; processed meats and seafood have also been implicated. Symptoms of watery diarrhea, vomiting, and fever develop within two to three days of infection. Although most patients recover quickly on their own, pregnant women, elderly people, diabetics, and people with weakened immune systems can develop life-threatening blood infections and meningitis; pregnant women may miscarry. Because of these risks, doctors often prescribe antibiotics for patients with intestinal Listeria.

Norovirus. This common food-borne infection has caused large outbreaks on cruise ships, in medical facilities and schools, and in many other settings. The virus spreads when someone consumes water or food contaminated with tiny amounts of fecal material from someone with the infection. The major symptoms are nausea, vomiting, and watery diarrhea. Most victims recover in one to three days, but dehydration can be troublesome. Antibiotics are ineffective against viruses, including this one.

Other culprits. A long list of microbes can cause food-borne infections. The perpetrators include viruses (hepatitis A, often from contaminated shellfish); bacteria (shigella, Vibrio species, and others); parasites (Giardia, Cyclospora, and others); and even prions ("mad cow disease" from contaminated beef; there have been about 200 human cases worldwide, but none have originated in the U.S.). It's enough to make you sick — and more than enough to spur you to take simple steps to reduce your risk.

Personal prevention

Food-borne infections are hardly new, and the simple steps that will protect you and your family are also familiar. Here's an update on the good advice your mother gave you:

  • Choose reputable markets and restaurants for shopping and eating out.

  • Wash your hands thoroughly before and after you prepare food, before you eat, and after you use the bathroom.

  • Wash your foods, including fruits and vegetables, poultry, fish, and meats. Use a brisk stream of clean water to dislodge surface bacteria and rinse off chemicals. Whole fruits and vegetables are safer than packaged and pre-cut produce.

  • Wash your utensils and cutting boards with soap and water. Use your utensils for one food at a time, and then wash them before switching to another food to reduce cross contamination.

  • Do not consume unpasteurized dairy products or juice or uncooked meat and poultry. Pregnant women and people with weakened immune systems should not eat raw fish, including sushi.

  • Cook your food thoroughly, using a meat thermometer to be sure the internal temperature of meat and poultry reaches at least 165F (180F for whole poultry). Cook eggs until the yolks are firm. Do not order rare meat or soft eggs at restaurants.

  • Refrigerate foods promptly, always within 2 hours (1 hour at room temperatures of 90F or more). Keep your refrigerator temperature at 40F or lower, keep your foods covered, and don't save leftovers for more than a few days. Keep your freezer at 0F or lower. Thaw frozen foods in the refrigerator or microwave, not at room temperature.

  • Reheat foods thoroughly, until they are piping hot.

  • Don't eat food that looks, smells, or tastes funny. When in doubt, throw it out.

People with food-borne illnesses should use disposable plates, cups, and utensils until they're recovered. Bathroom areas should be thoroughly cleansed with bleach-based products.

Beyond contamination

Mention food safety, and you'll conjure up images of killer spinach, toxic peanuts, and harrowing hamburgers. Microbial contamination gives these foods, and many others, their bad name. And for some people, chemical additives and pesticides are nearly as worrisome.

These are all important issues, but they're just the tip of the iceberg. Our greatest danger comes not from the bad things in food but from the "good" things. In today's America, an excess of calories heads the list, which also includes too much salt, sugar, and saturated fat.

Food safety reform starts with you. To be sure, that means handling food properly. But it also means choosing the right foods and eating the right amounts. And it means exercising enough to burn off excess calories.

All humans eat to live. Many in our affluent society live to eat. Do it right and you can have it both ways.

As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.