In perishable food items such as cream cheese, bacteria begin to grow most rapidly at temperatures above 40 F. Bacteria can double its re-population rate in as little as 20 minutes. The FDA estimates that 6.5 to 33 million illnesses and 9,000 deaths annually are caused by unsafe handling of food.

There are six kinds of bacteria related to food poisoning that cause the most hospitalizations in the U.S. Salmonella tops the list. It thrives in food items such as cream cheese and desserts filled cream cheese fillings that have been left unrefrigerated, and the number of cases of Salmonella in the U.S. has been on the rise since 1992. Symptoms occur six to 48 hours after the contaminated food has been consumed.

Unlike mold, the presence of bacteria such as Salmonella cannot be detected by the smell, taste or appearance of food. A bagel with cream cheese that has been sitting out unrefrigerated for more than two hours should be thrown away without tasting. If the air temperature reaches 90 F or hotter, the risk of harmful pathogens occurs after only one hour.

In order to survive, bacteria need food, moisture and warmth. Refrigerating perishable food items such as cream cheese at or below 40 F prevents the growth of harmful pathogens. Leaving a bagel with cream cheese out at room temperature for more than two hours and then refrigerating it might slow the growth of bacteria, but it will not kill the harmful bacteria that are already present.