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Parents were not successful in keeping perishable items such as meat, dairy and vegetables in sack lunches of preschool-aged children in a safe temperature zone before the food was eaten. (Paul Sakuma/Associated Press)

More than 90 per cent of preschoolers' packed lunches were kept at unsafe temperatures, even those with multiple ice packs, a new U.S. study finds.

When researchers tested 705 lunches at child care centres in Texas, they found only 1.6 per cent or 22 of perishable foods — such as meat, dairy products and vegetables  — were in the safe temperature zone, they reported in Monday's issue of the journal Pediatrics.

Fawaz Almansour, a doctoral student at the University of Texas in Austin and his co-authors said that to their knowledge, no study has documented the temperature of foods in packed lunches at child care centres, which is why they set out to take the measurements. 

Common sources of foodborne illness

Sources of illness: Raw and undercooked meat and poultry. Symptoms: Abdominal pain, diarrhea, nausea, and vomiting. Bacteria: Campylobacter jejuniE. coli O157:H7, L. monocytogenes, Salmonella.

Sources of illness: Raw foods; unpasteurized milk and dairy products, such as soft cheeses. Symptoms: Nausea, vomiting, fever, abdominal cramps, and diarrhea. Bacteria: L. monocytogenes, Salmonella, Shigella, Staphylococcus aureus, C. jejuni.

Sources of illness: Raw and undercooked eggs. Raw eggs are often used in foods such as homemade hollandaise sauce, caesar and other salad dressings, tiramisu, homemade ice cream, homemade mayonnaise, cookie dough, and frostings. Symptoms: Nausea, vomiting, fever, abdominal cramps, and diarrhea. Bacterium: Salmonella enteriditis.

Sources of illness: Raw and undercooked shellfish. Symptoms: Chills, fever, and collapse. Bacteria: Vibrio vulnificus, Vibrio parahaemolyticus.

Sources of illness: Improperly canned goods; smoked or salted fish. Symptoms: Double vision, inability to swallow, difficulty speaking, and inability to breathe. Seek medical help right away if you experience any of these symptoms. Bacterium: C. botulinum.

Sources of illness: Fresh or minimally processed produce; contaminated water. Symptoms: Bloody diarrhea, nausea, and vomiting. Bacteria: E. coli O157:H7, L. monocytogenes, Salmonella, Shigella, Yersinia enterocolitica, viruses, and parasites.

Source: U.S. National Digestive Diseases Information Clearinghouse

Previous studies by the U.S. Centers  for Disease Control and Prevention showed that children younger than four have 4.5 times the number of incidences of bacterial infection transmitted through food  compared with adults aged 20 to 49, which is why the researchers focused on preschoolers.

To minimize the risk of foodborne illness for people of all ages, Health Canada recommends that consumers always refrigerate food and leftovers promptly at 4 C (40 F) or below and to reheat leftovers to an internal temperature of 74 C (165 F) before eating.

Bacteria multiply fastest at temperatures between 4 C and 60 C.

In the study, researchers measured the sack lunches about 1.5 hours before the food was served.

They found:

  • 39 per cent of the lunches had no ice packs.
  • 45 per cent had at least one ice pack.
  • 88 per cent of lunches were at ambient temperature.

Many foods were not in an acceptable temperate range when measured, including:

  • 97 per cent of meats.
  • 99 per cent of dairy.
  • 98.5 per cent of vegetables.

"Results from this study indicate parents were not successful in keeping perishable items such as meat, dairy and vegetables in the sack lunches of preschool-aged children in a safe temperature zone before consumption," the study's authors concluded.

"Our results also highlight the need for additional research and action on the development of ice packs, lunch bags and other tools to maintain food in sack lunches in the safe temperature zone."

Only 12 per cent of the lunches were stored in refrigerators and the rest were kept at room temperature in the classroom.

Overall, 91 per cent of the lunches were packed in thermally insulated bags.

The study's authors acknowledged limitations of the study, including the timing of the measurements. Since children could start eating snacks in their lunches as early as one hour before lunch time, the authors chose 1.5 hours before lunch to take the temperature readings.

The researchers also just measured the surface temperature instead of the core temperature to avoid cross-contaminating foods. On the other hand, all items in the bag were measured, instead of just taking the collective temperature, the authors said.

The study was sponsored by Kuwait University and the U.S. National Cancer Institute.