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7 August 1998

Vol. II, No. 3

Health Matters


Don't let food spoil your picnic: preventing contamination

I've been reading about bacterial outbreaks in food lately, and I wonder if it is risky to cook hamburgers and hot dogs on the grill and then leave them on the picnic table?

"It depends on how well you cooked the meat and how long it's been sitting on the table," says Sam Donta, M.D., physician in infectious diseases at Boston Medical Center and professor of biomolecular medicine at Boston University School of Medicine.

Donta stresses that the best way to prevent bacterial growth on any kind of meat is by cooking it well. Heat eliminates the bacteria already living in the meat, and the more intense the heat, the more bacteria are killed. The longer food is left unrefrigerated, the more time you give the surviving bacteria to reproduce. While your body's natural defenses will eradicate a certain number of bacteria, if too many bacteria are present, the body cannot kill them all. They can then produce toxins, and food poisoning results. Thus, the two most effective ways of reducing the risk of food poisoning are to cook meat well and to eat it as soon as it is cooked. "Wrapping the meat in tinfoil will not affect the time it takes the meat to spoil," Donta adds.

Each type of meat has its own particular set of bacteria. Beef harbors E. coli; chicken contains campylobacter and salmonella (which is also found in milk and eggs); raw oysters and clams host vibrio hemolyticus, shigella, and hepatitis A; seafood and bottom-dwelling fish such as grouper and orange roughy contain high amounts of the chemical histamine, which can produce a reaction similar to bacterial infestation. While all of these bacteria and chemicals act on the body in different ways, one shared characteristic is that they work quickly, so the time between eating and the onset of symptoms is almost always a matter of hours. "If a person has symptoms similar to food poisoning, but it's more than 24 hours after eating a potentially risky food, it's probably not food poisoning," says Donta.

In addition to the bacteria in meat and seafood, other picnic foods can pose potential risks. For instance, gravy and barbecue sauce can contain spores that if left on the meat can germinate in three to four hours, producing the bacteria clostridium perfringens. Potato salad and pudding can be sites for contamination by staphylococcus aureus, a common bacteria usually called staph. Contaminated stuffing can sometimes lead to infection by B. cereus.

Symptoms of infection are different for each specific bacteria. "Bacteria from beef and chicken typically need eight to twelve hours before producing symptoms, and the main symptom is diarrhea," says Donta. "Staph infections from potato salad or allergic reactions to histamine from seafood tend to produce more vomiting than diarrhea, which can start as early as 30 minutes in the case of histamine or one or two hours with staph." He cautions that vomiting and diarrhea are not absolutely indicative of one type of infection or another.

Donta makes these simple recommendations to reduce the risk of food spoilage:

  • Cook well meats of all kinds and eat them as soon as they are cooked.
  • Wash your hands whenever you handle food, and try to avoid touching food if possible.
  • Don't work with food if you have a viral infection such as a cold or flu.
  • Once you've cooked the meat, don't return it to the platter it came from.
  • Wash oysters and clams before shucking, and eat them immediately thereafter.
  • Reheat any meat that has been sitting for more than a short time, especially if it has gravy or sauce on it.

These precautions should allow you to enjoy your picnic free of care. Pass the mustard and pickles.

"Health Matters" is written in cooperation with staff members of Boston Medical Center. For more information on food contamination or other health matters, call 638-6767.