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'Prewashed' Salads May Need Another Rinse

Consumer Reports Analysis Finds Bacteria in Packaged Green Salads
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WebMD Health News
Reviewed by Louise Chang, MD

Feb. 3, 2010 -- Those "prewashed" and "triple-washed" bagged salad greens in the produce section of the supermarket may not be as clean as you think.

In a new investigation from the Consumers Union, which publishes Consumer Reports, high levels of bacteria commonly linked to poor sanitation and fecal contamination were found in many of the sampled packaged salads.

The bacteria did not pose a health risk to the public, but their presence indicated a higher likelihood of contamination with rare but potentially deadly pathogens like E. coli and salmonella, Consumers Union senior scientist Michael Hansen, PhD, tells WebMD.

An E. coli outbreak in the fall of 2006 traced to packaged fresh spinach killed three people and hospitalized more than 100.

The cause of the contamination was never confirmed, but the E. coli is widely believed to have reached the spinach through groundwater that contained the feces of cattle and pigs.

Oldest Produce Had Most Bacteria

Consumer Reports investigators sampled 208 packaged salads, representing 16 brands purchased last summer in Connecticut, New Jersey, and New York. The salads were sold in either bags or plastic clamshell containers.

They found that 39% of the samples contained more than 10,000 "most probable number" per gram -- a measure of total coliforms, which are bacteria associated with fecal contamination. And 23% had more than 10,000 colony forming units (CFU) per gram of the bacterium enterococcus.

According to the report, experts contacted by Consumer Reports considered these levels unacceptable.

Bacteria levels varied widely, with some samples containing undetectable levels and others containing more than 1 million CFUs per gram, Hansen says.

Among the other findings:

  • Packaged produce tested at least six days from their use-by date tended to have lower levels of the bacteria than produce tested within five days of the use-by date. 
  • Salad mixes that included spinach tended to have higher bacteria levels than those without spinach. 
  • Contamination levels were similar whether the produce was packaged in a bag or clamshell container. And samples labeled "organic" were just as likely to have high levels of the bacteria as other samples. 
  • Little difference was seen in bacteria levels between larger, nationally distributed brands and smaller, regional brands. All brands with more than four samples had at least one package with relatively high levels of total coliforms or enterococcus.

Hansen says consumers should look for products that are at least six days from their use-by date when buying packaged salad products.

And products labeled "prewashed" or "triple-washed" should be washed again, even though this probably won't remove all bacteria, he says.

The report was made public online this week and it appears in the March issue of Consumer Reports.

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