Temperature is key to reducing risks.

• Position: Food Poisoning

Ants and bad weather are not the only things that can ruin a picnic. When food gets too hot or cold, the chances of contamination and food-borne illness increase. Taking a few preventative measures when dining outdoors can reduce the risk of food poisoning greatly. The Centers for Disease Control and Prevention, Atlanta, estimates that food-borne diseases cause 76,000,000 illnesses, 325,000 hospitalizations, and 5,000 deaths in the U.S. each year. Symptoms include upset stomach, abdominal cramps, nausea and vomiting, diarrhea, fever, and dehydration.

"As the weather gets warmer, people have to be more cautious about the temperature of food," warns Richard Fancher, sanitarian in the University of Missouri's Department of Environmental Health and Safety, Columbia. "The temperature danger zone for food is 41[degrees] to 140[degrees]F. This means people should try to keep food temperatures outside of this range, as bacteria reproduce and grow best in the temperature danger zone."

Outdoor diners especially should be careful of mayonnaise, which is a common ingredient in popular picnic foods--including sandwiches and potato and macaroni salad. Mixed with eggs, mayonnaise is susceptible...