Whether they are in backpacks, cubbies or desks, lunches packed for schoolchildren often sit around for three to four hours in various states of refrigeration before the lunch bell ever rings. This simple observation inspired some researchers from the University of Texas-Austin to ask the question: Do preschoolers’ packed lunches meet recommendations for safe food temperatures?


The answer, the team found, was a resounding “No.”

And while their study does not quantify illness, the authors do suggest that some improperly packed lunches could be leading to upset stomachs or illnesses in children.

As anyone who has ever acquired a food handler’s permit likely recalls, the Centers for Disease Control and Prevention (CDC) advises against letting perishable foods linger in the “danger zone” of 40 to 140 degrees Fahrenheit for more than two hours. People with underdeveloped or weak immune systems, such as young children, are especially vulnerable to pathogens that grow most rapidly at comfortable temperatures in the danger zone.

The study, published in the journal Pediatrics on August 8, examined 1,361 meat, dairy and vegetable items in 705 packed lunches from 235 preschool children (ages 3 to 5) on three separate days at random. After measuring the temperatures of the foods approximately 90 minutes before lunchtime, they found only 22 items below the CDC’s recommended 40 degree baseline.

In total, 97.4 percent of meat, 99 percent of dairy and 98.5 percent of vegetables measured above 40 degrees.  Nearly half (49 percent) of the lunches contained at least one ice pack, while 12 percent sat in school refrigerators, and yet the vast majority of these cooled lunches did not meet the recommended temperature. The remaining 39 percent had no devices to keep the food chilled.

“When we looked at this data we were really, really surprised,” said Sara Sweitzer, Ph.D., co-author of the study, dietician and postdoctoral researcher at the University of Texas-Austin.

Sweitzer’s team first gathered its data as part of a study on nutrition in packed lunches. The intention was to better educate parents on healthy eating, but when they started measuring temperatures, they uncovered this entirely different issue, and decided that parents needed some pointers.

To start, the authors recommend freezing lunchboxes along with ice packs, as ice packs in warmer containers expend extra energy cooling them. Sweitzer also suggested parents store non-refrigerated items separately and take greater care in regularly washing out lunch containers just as they would wash any other dishes that touch food, because bacteria can grow on small amounts of food that stow away.

Their most important advice, however, is for parents to wash their hands before preparing food, as most pathogens that could potentially grow to illness-inducing quantities will likely come from contact contamination, such as wiping a nose and then touching food. Still, the easiest way to ensure lunches stay safe is to make sure they are sufficiently cooled when they leave the house.

“These perishable foods can sit in the danger zone for up to two hours before they really start to become a risk,” Sweitzer said. “You want to pack that lunch so that it’s in the safe zone for at least the first few hours, and then they can eat it within the next two hours. The goal doesn’t have to be to keep it in the safe zone the entire time.”

But what risk do children really run if they eat a turkey sandwich that sits in the danger zone for three or four hours? As Sweitzer explained, it is difficult to say. She went through her entire school career carrying sandwiches in a brown paper bag, though her use of mayonnaise — an acidic preservative — might have helped her avoid getting sick.

“This is not a major outbreak of foodborne illness that the CDC can trace; it’s potential, minor illnesses,” she said. “It’s a matter of being aware of it. Parents today are more aware of it than, say, my parents were, and that’s a good thing. We’re not jumping to conclusions about children getting sick.”

Microbiologist and eFoodAlert author Phyllis Entis agrees that the potential exists for children to get sick from food that sits at room temperature for as little as three or four hours. But if parents handle the food safely, use fresh ingredients and maybe lather on a little mayonnaise, the likelihood of an illness drops significantly.

The most likely source of an illness, Entis said, would be from improper handling followed by poor temperature control. If parents wipe their nose, for example, and continue preparing a lunch, they run the risk of contaminating food with Staphylococcus aureus, the most common bug associated with poorly cooled food.

“That can cause nausea, vomiting for 24 hours — that ‘wish-I-was-dead-but-I-know-I’ll-live’ kind of sickness,” Entis said. “Staph is a natural, totally innocuous resident of the nasal passages that doesn’t do harm to the individual unless it contaminates food like that. It’s been with us as long as we’ve had noses.”

Entis reiterated that the colder the food is, the slower the microbes will grow and the safer the food will stay. The more accurate information and recommendations made to parents, she said, the better.

And that is exactly what Sweitzer said her team hoped to provide.

“This is all something for parents to think about as we get ready to start the new school year,” she said. “It just comes down to careful, easy practices.”

The full study, “Temperature of Foods Sent by Parents of Preschool-aged Children,” can be read online at http://pediatrics.aappublications.org/content/early/2011/08/04/peds.2010-2885.abstract.