Recent tests done by Consumer Reports found listeria on six samples of greens randomly purchased at grocery stores. The consumer watchdog tested 284 samples of lettuce, spinach, kale and other leafy greens purchased between June 3 and 19 at grocery chains in Connecticut, New Jersey and New York including Costco, Whole Foods, Acme and Hannaford.

Two of the contaminated samples were packaged — one was prewashed spinach and one was an organic spinach spring mix. The other four were loose heads or bunches of kale, green leaf lettuce, red leaf lettuce and spinach, Consumer Reports said.

One sample — a "triple-washed" Natures Place Organic Spinach Spring Mix from Hannaford — had a strain of the pathogen linked to two listeriosis cases reported to the Centers for Disease Control and Prevention. Consumer Reports said it wasnt known whether those who fell ill had eaten leafy greens. A Hannaford spokesperson told the organization it had not received any reports of illness associated with the product.

No other pathogens that cause foodborne illness found
Consumer Reports said recent illness outbreaks linked to romaine lettuce and other leafy greens prompted it to test the items. The group emphasized it did not find other pathogens that cause foodborne illness such as E. coli or salmonella.

Listeria can grow in refrigerated temperatures, so it can be particularly challenging to control. And while listeriosis isnt as common as other foodborne illnesses, it can be serious or fatal to pregnant women, the elderly and those with compromised immune systems.

The testing didnt cover a large enough sample to draw safety conclusions about specific brands or retailers, but Consumer Reports said the results were nevertheless concerning and had been immediately shared with the Food and Drug Administration, the CDC and affected marketers and retailers.