Reusable Grocery Bags Breed Bacteria, Research Says

Reusable grocery bags can serve as a breeding ground for dangerous food-borne bacteria and pose a serious risk to public health, according to a joint food safety research report issued by researchers at the University of Arizona and Loma Linda University. The study -- which randomly tested reusable grocery bags carried by shoppers in the Los Angeles area, San Francisco, and Tucson, Ariz. -- also found consumers were almost completely unaware of the need to regularly wash their bags.

"Our findings suggest a serious threat to public health, especially from coliform bacteria including E. coli, which were detected in half the bags sampled,” said Charles Gerba, Ph.D., a University of Arizona environmental microbiology professor and co-author of the study. “Furthermore, consumers are alarmingly unaware of these risks and the critical need to sanitize their bags after every use.”

The bacteria levels found in reusable bags were significant enough to cause a wide range of serious health problems and even lead to death -- a particular danger for young children, who are especially vulnerable to food-borne illnesses, he said.

The study also found that awareness of potential risks was very low. A full 97 percent of those interviewed have never washed or bleached their reusable bags, said Gerba, who added that thorough washing kills nearly all bacteria that accumulate in reusable bags.

The report comes at a time when some members of the California State Legislature, through Assembly Bill 1998, are seeking to promote increased consumer use of reusable bags by banning plastic bags from California stores.

"If this is the direction California wants to go, our policymakers should be prepared to address the ramifications for public health," said co-author Ryan Sinclair, Ph.D., a professor at Loma Linda University’s School of Public Health.

The report notes that "a sudden or significant increase in use of reusable bags without a major public education campaign on how to reduce cross contamination would create the risk of significant adverse public health impact."

Geographic factors also play a role, said Sinclair, who noted that contamination rates appeared to be higher in the Los Angeles area than in the two other locations -- a phenomenon likely due to that region's weather being more conducive to growth of bacteria in reusable bags.

The report, "Assessment of the Potential for Cross Contamination of Food Products by Reusable Shopping Bags," offers the following policy recommendations for lawmakers, as well as tips for consumers who use reusable grocery bags:

  • States should consider requiring printed instructions on reusable bags indicating that they need to cleaned or bleached between uses;
  • State and local governments should invest in a public education campaign to alert the public about risk and prevention;
  • When using reusable bags, consumers should be careful to separate raw foods from other food products; cross-contamination problems arise when foods that people eat raw, such as apples and lettuce, are placed in a bag that has carried meat;
  • Consumers should not use reusable food bags for such other purposes as carrying books or gym clothes;
  • Consumers should not store reusable bags in the trunks of their cars because the higher temperature promotes growth of bacteria.

In one test, Gerba and researchers took a reusable bag that had carried meat and placed the bag in a car trunk. He said new bacteria grew in two hours. He added that in previous bacteria studies he has found a toilet seat typically has 50 coliform bacteria; in these latest studies, the reusable bags had 500 to more than 1,000 coliform bacteria.

"As scientists, our focus was not on the relative merits of paper, plastic, or reusable grocery bags," Gerba said. "Our intent was purely to provide relevant data to better inform consumers and lawmakers about the public health dimensions that could arise from increased use of reusable bags. With this knowledge, people will be in a better position to protect their health and that of their children."

Gerba noted that the field research for the report was conducted according to established scientific methodologies and best practices. The sample tested included 84 actual consumer reusable bags (25 in Los Angeles, 25 in San Francisco, 34 in Tucson). New reusable bags and plastic bags were tested; none contained any contamination. The American Chemistry Council provided funding to support this study, which, according to Gerba, cost about $30,000.