Harvard Men's Health Watch

Food-borne illnesses, Part I: The big picture

Peanuts and peppers, hamburgers and spinach, chicken and cheese, even cookie dough. Nearly every week, it seems, there's another scare about contaminated foods and the epidemics that result. What's gone wrong with America's food supply? And what can we do, as individuals and as a society, to be sure our food is safe and healthful?

Then and now

Although food-borne illnesses are a major worry today, the problem is far from new. Just 100 years ago, in fact, large numbers of Americans were contracting tuberculosis from contaminated milk, typhoid fever and cholera from tainted water, and trichinosis from infected meat. These life-threatening problems have been all but eliminated, thanks to pasteurization of milk, improvements in canning and refrigeration, better sanitation, and disinfection of water supplies. Despite all this progress, food-borne illnesses have stayed with us, and in recent decades, the problem has taken on new dimensions.

Many factors contribute to the renewed concern about food safety. Agriculture and food processing have grown enormously in scale, and foods are shipped large distances within the U.S. — and into the U.S. from around the world. Contamination in one place can produce illnesses at great remove, making it difficult to recognize an outbreak quickly and even harder to track down its source. Large-scale ranching and farming practices mean that animals are often crowded together, so harmful bacteria can spread quickly. Because antibiotics are routinely added to animal feed, these bacteria are increasingly drug-resistant. As eating habits change, Americans are dining at restaurants more often, thus losing control over food handling and preparation. As our population ages, there are more elderly and chronically ill individuals who are particularly susceptible to food-borne infections. And just when we need help the most, the nation's food safety agencies are underfunded, fragmented, and overwhelmed.

Fortunately, these issues haven't brought back botulism and cholera. But they have resulted in some 76 million food-borne infections in the U.S. each year, 350,000 of which are serious enough to require hospitalization and 5,000 of which are lethal. And food-borne illnesses add $7 billion to America's annual health care costs just when we can afford it least.

Infection or intoxication?

There are two major types of food-borne illnesses.

"Food poisoning" sounds fearsome, but, except for the rare case of botulism, it's actually the milder problem. In this scenario, food becomes contaminated by a bacterial pathogen, usually a Staphylococcus, Clostridium, or Bacillus species. The bacteria produce a toxin, which remains in the food. Subsequently, cooking knocks off the bacteria without destroying the toxin. People who eat food laced with the toxin develop cramps and diarrhea within six to 12 hours, sometimes with vomiting. It can feel miserable and may produce dehydration, but food poisoning never causes fever or intestinal bleeding, and the symptoms resolve on their own within a day or so. Because the illness is triggered by a toxin, not living bacteria, food poisoning is an intoxication, not a true infection.

Food-borne infections are more serious because contaminated foods contain live microbes, which multiply within the patient's intestines and can sometimes invade the bloodstream and spread to other organs. In addition to cramps and diarrhea, victims often have fever, and they sometimes develop complications in other organs. Most food-borne infections remain confined to the intestinal tract, and most resolve without antibiotics in less than a week. Still, very serious infections can occur, and they require serious treatment.

Good bugs, bad bugs

The human intestinal tract is home to 10 times more bacterial cells than there are human cells in the entire body. There are up to 1,000 species of bacteria in the colon; most are harmless, and some can actually help preserve good health by breaking down harmful chemicals, producing vitamin K, and crowding out dangerous bacteria.

We live in harmony with our 100 trillion intestinal bacteria because they're our bugs, and we're used to them. But one man's friend can be another's foe. Sometimes the foes live in another person's intestines, but more often they reside in the innards of cattle, poultry, and other animals. Fruits, vegetables, nuts, and other products can be contaminated by animal or human manure right in the field or at any time in the long chain that leads from farm to table. Meat and poultry can also be contaminated in the slaughterhouse, and since ground beef and sausage contain meat from many animals that is mixed together during processing, a single episode of contamination can spread widely.

The inside job

When you ingest a preformed toxin, it goes to work at once; that's why food poisoning starts so soon after you down the contaminated chow. But food-borne infections don't cause any symptoms for one to seven days. During this incubation period, the bacteria set up shop in the intestinal tract As the bad guys grow and multiply, they produce toxins and other harmful products. When enough have accumulated, they rough up the intestinal lining, causing cramps, fever, and diarrhea, which may be bloody. That's bad enough, but if some bacteria sneak into the bloodstream, dire problems can develop. Fortunately, this is uncommon, and, in most cases, the body can recover on its own, usually in about three to five days.

Fighting back

The body has several ways to check food-borne microbes. Stomach acid and the digestive enzymes that break down food into nutrients can kill some bacteria, particularly if the food is lightly contaminated. The immune system can produce antibodies and mobilize white blood cells that target bacteria, though the process is slow. Bacteria that sneak into the bloodstream can be filtered out by the liver and spleen and gobbled up by white blood cells, limiting harm. And even the diarrhea that's so very unpleasant can serve a useful purpose by expelling microbes and their nasty products from the body. That's why doctors discourage the use of antidiarrheal medicine for bacterial infections, making exceptions for severe symptoms with dehydration. Similarly, it's usually better to let your body control the infection on its own, but doctors will prescribe antibiotics for patients with severe symptoms or complications. Patients with impaired immune systems are likely to need antibiotics; the very young and very old are also highly vulnerable to food-borne infections.

Prevention is, of course, the best way to fight back. That means enhanced efforts by agriculture, industry, and government to establish and enforce food safety standards and to inspect and test foods before they reach your plate. And you can help, too, by following simple precautions for storing, handling, and preparing food.

Prevention: Food safety reform

It's important for all of us to shop wisely and to handle food safely at home. But for full protection, we have to be sure food is safe when it arrives at the market. That means preventing microbial contamination, and it also requires weeding out chemical contaminants, ranging from unsafe levels of pesticides, antibiotics, and hormones to adulterants such as the melamine that tainted the food supply in China in 2007.

The USDA is responsible for the safety of meat, poultry, and processed eggs, while the FDA supervises most other foods. But between 2003 and 2007, the FDA division that shoulders most of the load shed 600 inspectors and 20% of its scientists. Thirteen other federal agencies, operating under 30 different laws, are also in the mix. It's a patchwork system with plenty of gaps. It's also severely under-resourced and ill-equipped for the globalization of our food supply and the threat of bioterrorism. In fact, although we now rely on imports for 15% of our food supply (including 60% of our fruits and vegetables and 75% of our seafood), just 1% of our food imports are inspected.

We need federal, state, and local government reform, and we also need the full cooperation of the private sector, including importers, farmers, ranchers, and the food processing industry. It's a tall order; to make it happen, we'll all have to do our part as informed, active consumers and voters. And we also need to consider new approaches that can help.

Prevention: Food irradiation

With so much worry about our food supply, you'd think we'd be doing everything in our power to prevent food-borne infections. But we're not. There are many ways to improve the situation; some will require major reforms by the private sector and government, but one of the most helpful is ready to go. It doesn't require new technology or expensive research. But it does require a new mindset, since many consumers are scared off by its name: irradiation.

Pasteurization kills bacteria in food with energy from heat; irradiation kills microbes with energy from ionizing radiation. The energy can be generated in the form of electron beams, x-rays, or gamma rays. The process is quick and does not raise the food's temperature. The energy passes right through the food, and the food that emerges is not radioactive, any more than you are radioactive after you have a chest x-ray or CT scan. And irradiated food retains its appearance, flavor, and nutritional value.

Food irradiation has been in use for decades. It is approved in over 40 countries, and extensive experience with animals and people (including American astronauts) who have eaten irradiated food has not revealed any increased risk of cancer or other health problems.

Many government agencies and independent organizations have endorsed food irradiation. The list includes the FDA, CDC, Department of Agriculture, American Dietetic Association, American Academy of Pediatrics, and the World Health Organization. In the U.S., irradiation is approved for herbs and spices, meat and poultry, fruits, vegetables and seeds, eggs, and wheat. Even so, only 10% of our herbs and spices and just 0.002% of our other foods are irradiated. Ironically, perhaps, many medical supplies — from bandages to implanted devices — are sterilized by irradiation without triggering any consumer protests.

Irradiated food won't budge the meter on a Geiger counter, but it sets the dial spinning on talk radio. Consumers should have their say, and they'll always have the freedom to choose since all irradiated foods are labeled as such. Packages also bear the universal symbol for irradiation, the radura (pictured here).

illustration of the symbol for food that has been irradiated

Food irradiation is not a cure-all; even if it were widely adopted in the U.S., we'd still need all the other steps to improve food safety. Still, the CDC estimates that if food irradiation were used for just half the meat and poultry consumed in the U.S., we'd eliminate 900,000 cases of food-borne illnesses and prevent 352 deaths in a year. Perhaps warning labels should be affixed to food that has not been sterilized by irradiation.