Salad fad can't explain spinach, lettuce scares

CHICAGO (Reuters) - An increase in the number of foodborne illnesses caused by contaminated spinach or lettuce over the past 35 years cannot be explained by increases in salad consumption over the same period, U.S. government researchers said on Monday.

They said the findings reinforce the need for local, state and federal health authorities to monitor preparation of leafy green vegetables from the point of harvest all the way through the food preparation process.

"Consumption of leafy greens has increased over the years, but it does not completely explain the increase in the proportion of foodborne outbreaks due to leafy green consumption," Dr. Michael Lynch, a researcher with the U.S. Centers for Disease Control and Prevention, said in a statement.

A spate of high-profile food safety scares in the past two years raised concerns among consumers, Congress and federal health regulators about the safety of the U.S. food supply.

Prompted by E. coli outbreaks linked with spinach and lettuce in 2006, Lynch and colleagues set out to study past outbreaks and see if some patterns could emerge.

"We wondered whether it was just related to more people and more people eating more leafy greens," Lynch said in a telephone interview.

Using CDC data, Lynch's team analyzed more than 10,000 disease outbreaks reported between 1973 and 2006. They presented their findings on Monday at the International Conference on Emerging Infectious Diseases in Atlanta.

They found about 5 percent of outbreaks were related to leafy greens. About 60 percent of those were caused by the norovirus, which causes "stomach flu," but 10 percent were caused by Salmonella bacteria and 9 percent were caused by E. coli 0157, a dangerous strain of the usually benign bacteria.

They found the number of cases of disease linked to leafy greens far outpace increases in salad consumption.

U.S. leafy green consumption rose 17 percent during 1986-1995 compared with the previous decade, but outbreaks of foodborne disease caused by leafy greens increased by 60 percent in that period.

In the 1996-2005 time frame, leafy green consumption rose 9 percent over the prior decade, but foodborne diseases outbreaks increased by 39 percent.

"Consumption is probably playing some role but it can't explain all of the increase in these leafy green outbreaks," Lynch said.

While some outbreaks can be traced to a local food preparation source, many are widespread, suggesting a problem in farm processing or at the processing plant," Lynch said.

(Reporting by Julie Steenhuysen, editing by Maggie Fox)