With Americans eating out more, researchers are cautioning that the plates on which commercial meals are served may become contaminated with bacteria if they are not allowed to dry properly before being piled up after washing.

Researchers assessed whether stacking wet dishes in commercial establishments may contribute to the growth of harmful bacteria on plate surfaces. According to the Centers for Disease Control and Prevention, there are an estimated 75 million cases of foodborne illnesses reported each year in the US.

The researchers first identified bacteria on 100 dishes (prior to washing) that had been used to serve meals to patients at a medical center. They then put half the plates through a full cycle of a dishwasher, stacking the plates after placing small amounts of water on each dish surface. The other 50 plates were machine-washed and then allowed to air dry for 24 hours.

Twenty-four hours after washing, the investigators found no apparent difference in bacterial growth between those stacked wet and those fully air-dried. However, after 48 hours a significantly higher amount of various bacteria were evident on the wet-stacked dishes.

Although the researchers did not determine exactly what types of bacteria had grown on the plates, they conclude that there is a risk of bacterial growth and food contamination if dishes are stacked wet after being run through an improperly working dishwasher or insufficiently dried after being hand washed.

Food safety and sanitation are of interest to consumers today because of mad cow disease, contaminated water supplies, overuse of antibiotics, the public eating outside the home more often. This time-temperature-moisture problem sets up an ideal environment for microbial growth.

The Food and Drug Administration code specifically recommends air drying of all commercial dishware in order to prevent such food contamination problems. And she stressed that consumers and food-preparers should pay attention not just to what they eat but to whether or not what they eat is safely prepared.

Journal of the American Dietetic Association August 2001;101:933-934