A new investigation by the Yonkers, New York-based Consumers Union has revealed that the salad greens packaged as “pre-washed” and “triple-washed,” appearing on the shelves of the supermarket’s produce section, may actually not as clean as they are perceived to be.

The Consumer Union study, which was based on the tests of 208 packaged salads, found that nearly 23 percent of the samples tested had Enterococcus levels, and 39 percent of them had levels of total coliforms.

Despite the presence of fairly high levels of bacteria, generally associated with poor sanitation and fecal contamination, in sampled packaged salads, Michael Hansen, a senior scientist at Consumers Union, opined that the bacteria did not pose any alarming health risk to the people.

Nonetheless, the presence of bacteria hints at the possibility of contamination with rare, but potentially poisonous, pathogens like E. coli and salmonella. In fact, an E. coli outbreak in 2006, which killed three and sickened over 100 people, was traced to packaged fresh spinach.

Highlighting the absence of federal standards for bacteria in salad products, Consumers Union has suggested that products labeled as “prewashed” or “triple-washed” should be washed again.

The group has also urged the Food and Drug Administration to “establish performance standards for these bacterial indicator organisms in all leafy greens as part of its ongoing effort to propose regulations on produce safety by October 2010.”