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CDC: Food-borne Illnesses Underreported

Improved Investigation and Analysis Would Reduce Toll of Food-borne Disease

By Bill Hendrick
WebMD Health News

Reviewed By Louise Chang, MD

June 11, 2009 -- Most food-borne illnesses that sicken millions of people in the U.S. annually and kill thousands are preventable, and the toll could be reduced with better reporting and analysis by health officials, the CDC says.

The agency reports in its June 12 Morbidity and Mortality Weekly Report that norovirus and salmonella were the leading causes of food-borne disease outbreaks in 2006, the latest year for which statistics are available.

Better surveillance and investigation could help control disease by pinpointing causes, such as improper food handling practices, the report says.

Ian Williams, PhD, chief of the OutbreakNet team at the CDC, tells WebMD that only a tiny fraction of food-borne illnesses are reported or recognized.

"Most cases are not associated with outbreaks, so this is just the tip of the iceberg," he says. "The interesting thing is that most cases are sporadic and aren't part of outbreaks. So what outbreaks do is provide a window in, to see what's going on in the larger picture. With most sporadic cases, we never figure out what causes them, that's why we need more emphasis on identification and analysis."

Williams says to get better data, local health authorities must do a better job of identifying causes.

"In order to track this we need the infrastructure at the state level to investigate and find out causes of outbreaks," Williams tells WebMD. "Also, the regulatory structure needs to be put in place to find out the causes and put programs in place to prevent the outbreaks to begin with."

Noroviruses are a group of related viruses that cause acute gastroenteritis, generally characterized by diarrhea, nausea, vomiting, and abdominal pain. Salmonella are bacteria that can cause diarrhea (which may be bloody), vomiting, nausea, fever, and abdominal cramps.

Outbreaks of Food-borne Diseases

In 2006, there were 1,270 reported food-borne disease outbreaks, resulting in 27,634 illnesses and 11 deaths. Of the outbreaks, 624 had a confirmed cause; 54% of the time it was norovirus, the CDC says. Eighteen percent were salmonella outbreaks.

Most illnesses, hospitalizations, and deaths caused by food-borne illnesses are not recorded. But the CDC estimates that such diseases sicken 76 million Americans per year, cause 300,000 hospitalizations, and cause 5,000 deaths.

Food-borne outbreaks of norovirus occur most often when infected food handlers fail to wash their hands well after using the toilet, the CDC says in a news release. Food-borne outbreaks of salmonella commonly occur when foods that have been contaminated with animal feces are eaten raw or insufficiently cooked.

In 2006, the food commodities associated with the largest number of illnesses were poultry (21%), leafy vegetables (17%) and fruits or nuts (16%).

The food commodity categories defined by the CDC are fish, crustaceans, mollusks, dairy, eggs, beef, game, pork, poultry, grains/beans, oils/sugars, fruits/nuts, fungi, leafy vegetables, sprouts, vine/stalk vegetables, and root vegetables.

"Determining the proportion of outbreak-associated cases of foodborne illness due to the various food commodities is an important step," Patricia M. Griffin, MD, chief of the CDC's Enteric Diseases Branch, says in a news release. "Identification of particular food commodities that have caused outbreaks can help public health officials and the food industry to target control efforts from the farm to the table."

She cautions, however, that only a small proportion of food-borne illnesses occur as part of recognized outbreaks. Some outbreaks aren't detected, investigated, or reported because many states lack the resources.

The authors write that timely reporting of results of investigations is an important step in efforts to better understand and define the epidemiology of food-borne disease in the U.S. and to identify gaps in the food-safety system.

Many food-borne illness cases are neither recognized nor reported, the CDC says, and thus are not recognized by health officials.

"Outbreak investigations, especially multistate outbreaks, can rapidly strain public health system resources," the authors write. "Enhancing capacity at local, state, and federal levels could make outbreak detection and investigation even faster."

A recent salmonella outbreak that sickened hundreds of people in the U.S. and Canada was traced to peanuts in Georgia. The outbreak was blamed for some deaths, though the exact number is not known.

SOURCES: News release, CDC. Morbidity and Mortality Weekly Report, June 12, 2009; vol 58. Ian Williams, PhD, chief, OutbreakNet team, CDC.

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