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Leafy Greens, Dairy Top Foodborne Illness Causes at Turn of 21st Century

Poultry leading cause of death

A review of eleven years of foodborne illness data has revealed that, between 1998 and 2008, leafy green vegetables and dairy sickened the greatest number of people, while poultry caused the most deaths.

Government researchers identified 4,589 outbreaks linked to one known food source during this time period. These outbreaks caused a total of 120,321 illnesses, which were used for the analysis, published ahead of print Tuesday in Emerging Infectious Diseases.

A full 46 percent of these illnesses were attributed to produce items, led by leafy greens, which alone accounted for 22 percent of illnesses. Dairy was the next leading source of sickness, linked to 14 percent of cases, followed by fruits and nuts.

More than half (56 percent) of all illnesses were caused by norovirus, a pathogen that causes gastrointestinal symptoms that usually resolve within a couple days, but can cause more serious illness in young children, the elderly or individuals with compromised immune systems.

While poultry took a smaller share of the illness pie (10 percent), it was the leading cause of food related deaths during this ten-year period, accounting for 19 percent of the estimated 1,451 deaths that occurred over this time period. The organisms that caused the most poultry related deaths were Listeria monocytogenes (63 percent) and Salmonella (26 percent).

Dairy was the leading cause of hospitalizations. The report did not look which of these dairy products were pasteurized versus raw, but that is something the agency intends to examine in the future, said Patricia M. Griffin, CDC’s Chief of Enteric Diseases and lead author of the paper.

“Sometimes we don’t know for a particular outbreak whether the item was raw or pasteurized,” said Griffin. “Because it’s not provided on the report form. We’re working with reporting agencies to make sure that’s really clear in the future.”

While this new report provides a picture of what foods were responsible for the most illnesses over more than a decade, it does not reflect changes that occurred during this time, noted Griffin.

“There are some particular things that were different in the beginning of this period we studied  from the end,” said Griffin.

For example, poultry-related deaths were more prevalent in the beginning of the window covered by the report, due to a number of Listeria outbreaks linked to deli turkey, she explained.

“Our last big multistate Listeria outbreak [linked to these foods] was in 2002,” said Griffin. “That was in the early part of the period that we’re reporting on in this paper. If we only looked at the last half of the period that we reported on for this paper, we’d have many fewer of those Listeria outbreaks, and they’re responsible for a lot of poultry-related deaths, so that’s a place where you might see a difference.”

Another change in outbreak sources over this time period was a decrease in illnesses from fruit juice. “Apple cider and even commercial, widely distributed apple juice that wasn’t pasteurized was harboring E. coli O157:H7 and Salmonella and parasites as well,” noted Griffin. Now, juice that’s sold across state lines must be pasteurized.

So what lessons can be drawn from looking at such a broad time period rather than at the ups and downs during that time?

“You get a more robust analysis if you include more data, and if you start trying to include fewer years, then you have a hard time making some good statistically significant statements about some of the less common agents in food,” said Griffin.

The analysis was conducted by researchers at the federal Centers for Disease Control and Prevention in order “to help determine priorities for food safety efforts,” according to the paper.

But while this report can be useful in deciding where to allocate food protection resources, “CDC does not make those sorts of recommendations,” said Patricia M. Griffin, one of the authors of the analysis, in an interview with Food Safety News. 

This report marks CDC’s second data dump of the week. The first, a review of foodborne illnesses from 2009 through 2010 was released on Monday. That one focuses on a smaller, more recent window of time.

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