She Knows reports that year after year, we hear and read the same advice: Handle food carefully in the summer because foodborne illness — also known as “food poisoning” — is more prevalent in warmer weather. Do foodborne illnesses increase during the summer months? If so, why?
Watch out for bacteria!
Yes, foodborne illnesses do increase during the summer, and the answer appears to be twofold. First, there are the natural causes. Bacteria are present throughout the environment in soil, air, water and in the bodies of people and animals. These microorganisms grow faster in the warm summer months. Most foodborne bacteria grow fastest at temperatures from 90 to 110 degrees Farenheit. Bacteria also need moisture to flourish, and summer weather is often hot and humid.

Given the right circumstances, harmful bacteria can quickly multiply on food to large numbers. When this happens, someone eating the food can get sick.
Second, there are the “people” causes for the upswing in summertime foodborne illnesses. Outside activities increase. More people are cooking outside at picnics, barbecues and on camping trips. The safety controls that a kitchen provides — thermostat-controlled cooking, refrigeration and washing facilities — are usually not available.
Fortunately, people seldom get sick from contaminated food because most people have a healthy immune system that protects them not only from harmful bacteria on food, but from other harmful organisms in the environment. At the same time, the Food Safety and Inspection Service, other government agencies and food producers go to great lengths to keep food safe. And, of course, consumers can protect themselves at home with proper refrigeration and thorough cooking of perishable food.