With back to school just around the corner, a new study that found bag lunches can be a breeding ground for bacteria may cause parents to reconsider what they pack in their child's lunch. Even ice packs don't necessarily help.

What the researchers found was startling. Nine out of ten of the items checked were at a temperature above 40 degrees and considered unsafe to eat, even if the packed lunch included an ice pack and even if the lunch was stored in the refrigerator.

University of Texas researchers visited nine of the state's child care centers and measured the temperatures of items in the sack lunches of over 700 preschool children 90 minutes before lunch time. A food item with a temperature of 40 degrees Fahrenheit or lower discourages the growth of bacteria and is considered safe to eat. Temperatures over 40 degrees encourage the growth of bacteria such as E. coli and Salmonella, which can cause vomiting, diarrhea, or in some cases, can lead to death.

What the researchers found was startling. Nine out of ten of the items checked were at a temperature above 40 degrees and considered unsafe to eat, even if the packed lunch included an ice pack and even if the lunch was stored in the refrigerator. The average temperature was more than 60 degrees. Of the nearly 1,400 food items tested, only 22 percent were at the right temperature. Less than two percent of the dairy, meat, and vegetable items were in a safe temperature zone. Parents had not included an ice pack in nearly 40 percent of the lunches in the study.

What can parents do to make their child's lunch safer to eat? Purchase an insulated lunch bag that comes with a frozen gel pack. Simple ice packs tend to melt quicker. Using more than one gel pack will help keep foods at the right temperature. If packing juice, freeze the juice box.

Lunches that include cheese, yogurt, or sandwiches made with lunchmeat and mayonnaise should be prepared the night before, refrigerated overnight, and ideally put in the refrigerator until lunch time the next day. Even though sandwiches made with lunchmeat and mayonnaise are more prone to spoilage, if that is what your child prefers, place the sandwich between two gel packs or between the gel pack and the frozen juice box for maximum chill. Fruit or vegetables than have been cut should be placed next to a cold source, too.

Alternatively, choose items that don't need to be refrigerated such as whole fruits and vegetables, breads, crackers, trail mix, raisins, and pickles. Shelf-stable fruit cups and applesauce are good choices that won't spoil, as are unopened packages of tuna or meats. You can't go wrong with peanut butter and jelly with a piece of fruit.

According to the Centers for Disease Control and Prevention, about 76 million people are victims of foodborne illness each year, and about 5,000 cases result in death. Children younger than four suffer 4.5 times the rate of food-borne illness that adults do.

The study is published in the September issue of Pediatrics.