Washing fresh fruits and vegetables -- even with disinfectants -- may not be enough to stop food poisoning, according to a report from the U.S. Department of Agriculture.

The report found that while washing helps reduce the chances of catching a bug, some microbes can hide too well, including getting inside the leaves of some produce.

But radiation kills microbes that go inside the food, including E. coli and salmonella, the agency said.

Fresh fruits and vegetables carry the risk of contamination because they are generally grown in open fields with potential exposure to pathogens from soil, water, manure, wildlife or other sources.

Using this technique on fresh and fresh-cut fruits and vegetables could provide a reliable way to reduce the numbers of foodborne illnesses reported each year in the United States, says Brendan A. Niemira, Ph.D., a microbiologist with the USDA's Agricultural Research Service in Wyndmoor, Pa., who directed the study.

In a study, scientists forced E. coli in spinach and lettuce leaves, then washed them with various methods and counted bacteria.

Plain water was not effective at reducing the levels of the pathogen. A sodium hypochlorite solution did not result in significant reductions of E. coli cells in spinach leaves, and an gave less than 90 percent reduction of E. coli in the romaine lettuce samples.

Ionizing radiation, in contrast, significantly reduced the pathogen population in both the spinach and the lettuce leaves by more than 99 percent.

Though some activist speak against irradiation, consumer confidence in the application has grown steadily through the years as studies have shown its effectiveness in reducing pathogens that cause foodborne illnesses, said Christine Bruhn, Ph.D., who focuses on consumer issues in food safety and quality at the University of California at Davis.