The location where foods are kept in the fridge matters as well. Foods that are kept in the door of the refrigerator can be 5 to 7 degrees warmer than other foods, Nelken says. It may not seem like a big difference, but when you consider the fact that many people keep sensitive foods such as eggs and milk in the door, it's a recipe for sickness. "Every time you open the refrigerator door, the food inside gets a blast of heat that raises the temperature," he adds.

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"Leftovers are a major source of foodborne illness. This occurs when people leave foods at a temperature I call the 'danger zone,' which is from 41 to 135 degrees. At the 70-90 degree range, bacteria can double every 20 minutes," Nelken says.

Leftovers should not be put in the refrigerator immediately after cooking. If they're still hot, it will take longer to get cool, and food will stay longer in that bacteria "danger zone" of 135 degrees and lower. And putting it in a sealed container actually locks in the heat. Nelken's suggestion -- put the food in the freezer for up to 30 minutes to stop the heating process and cool it more quickly. Large portions should be separated into smaller containers to distribute heat.

"Some people think putting food in the fridge makes it safe, but the refrigerator doesn't kill bacteria. It may slow it down, but it's more like bacteria hibernating for the winter," Nelken says.