A study was done to assess the potential for cross contamination of food products from reusable bags used to carry groceries.

Reusable bags were collected at random from consumers as they entered grocery stores in California and Arizona.

Reusable bags are seldom, if ever, washed and often used for multiple purposes.

Large numbers of bacteria were found in almost all bags, including coliform bacteria (bacteria which predominantly inhabit the intestines of warm blooded animals, including humans).  The presence of these bacteria indicated the possible presence of disease causing agents in half of the bags tested.  E. Coli was identified in 12% of the bags along with a wide range of enteric bacteria (bacteria that normally inhabit the intestines).

When meat juices were added to bags and stored in the trunks of cars for two hours, the number of bacteria increased 10-fold indicating the potential for bacterial growth in the bags.

Hand or machine washing was found to reduce the bacteria in bags by greater than 99.9%.

These results indicate that reusable bags can play a significant role in the cross contamination of foods if not properly washed on a regular basis.

The bags used were the woven polypropylene bags.

This potential exists when raw meat products and foods that are traditionally eaten uncooked (fruits and vegetables) are carried in the same bags, either together or between uses.  This risk can be increased by the growth of bacteria in the bags.