Botulism: Rare but Dangerous Type of Food Poisoning

Botulism is caused by potent toxins produced by the spore-forming bacterium Clostridium botulinum, which is common in soil. Any food that is contaminated by soil and is subsequently carelessly washed or mishandled may be a source of botulism. However, this microbe produces poisons only at temperatures above 38˚F and under certain conditions—notably an almost complete lack of oxygen—and so is quite rare.

Canned goods are a potential source of botulism. Modern commercial canning methods have gone far toward eliminating botulism from canned foods, but outbreaks still occur as a result of home canning. Though contamination usually causes cans to swell, the absence of swelling does not guarantee safety. Other warning signs in a can's contents are gas bubbles, discoloration, and milky liquids that normally should be clear.

Even if the spores are present, toxins won’t be produced unless food is left at room temperature for at least 12 to 24 hours and under relatively airless conditions—for example, a tight wrap or a coating of fat. The spores can be destroyed only by moist heat at 248˚F under pressure (in a pressure cooker, for instance) for 30 minutes, but the toxin will be inactivated if the food is brought to the boiling point (212˚F) for 10 minutes.

Precautions for Children

If you have a child enrolled in a day-care center, or if you work in one, make sure toilet and diaper-changing areas are separate from food-preparation areas. Also be sure that food is not prepared by staff members who provide diapering service. The diaper-changing areas should be cleansed with disinfectant after use, and any favorite toys should also be disinfected frequently.

If your child has been infected and still has active diarrhea, keep him or her at home until the infection has cleared to decrease the risk of further transmission.

Microwaving Microbes

While microwave ovens cook foods quickly and tend to destroy fewer vitamins than conventional cooking methods, they also may heat foods unevenly and leave some parts undercooked. This leaves open the possibility that bacteria may survive cooking. To be sure that your microwaved food doesn’t cause food poisoning, follow these guidelines:

  • To be sure that foods cook evenly, rotate all foods at various intervals during cooking.
  • Check the internal temperature of meat and poultry to be sure that they are cooked all the way through.
  • Wrap plastic made to be used in microwave ovens around the dish, or cover it with glass or ceramic. The trapped steam will help decrease evaporation and will heat the surface. Prick a hole in the plastic wrap to vent steam. The plastic wrap shouldn’t touch the food.
  • Allow microwaved food to stand covered after cooking. Heat concentrated on the inside will radiate outward through the food, cooking the exterior and equalizing the temperature throughout. Food will taste better this way, too, since it will be consistently hot.
  • Thaw meats before cooking in a microwave oven; most models have defrost settings for this purpose. Ice crystals in frozen foods are not heated well by microwaves and can leave cold spots.
  • If you’re used to conventional cooking, remember that the more food you’re microwaving, the longer it will take. For example, four baked potatoes will take much longer than two.


The Complete Home Wellness Handbook

John Edward Swartzberg, M.D., F.A.C.P., Sheldon Margen, M.D., and the editors of the UC Berkeley Wellness Letter

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 08 Aug 2010

Last Modified: 22 Jul 2015