Foodborne disease rates changed little in 2007

Apr 10, 2008 (CIDRAP News) – The rates of the most common foodborne illnesses in the United States have remained about the same since 2004, pointing to a need for increased efforts to ensure food safety, the Centers for Disease Control and Prevention (CDC) reported today.

In 2007, rates of infection with Campylobacter, Listeria, Salmonella, Shigella, E coli O157, and Yersinia did not decline significantly compared with the previous 3 years, according to data from the CDC's 10-state FoodNet surveillance system, the agency said.

The one exception to the static picture was the parasite Cryptosporidium, for which the estimated incidence of infections was up 44% compared with the 2004-06 period, the CDC said. Officials said the reason may be that a new treatment for the infection is spurring more testing for it.

Although some foodborne infections have declined significantly since surveillance began in 1996, the declines all occurred before 2004, the CDC said in a news release.

"The results show that prevention efforts have been partly successful, but there has been little further progress in the most recent years," Dr. Robert Tauxe, deputy director of the CDC's Division of Foodborne, Bacterial and Mycotic Diseases, said in the release.

"That indicates that further measures are needed to keep prevention on a downward track," Tauxe said at a news teleconference today. "The incidence of Salmonella actually has changed very little since those early years."

The FoodNet system compiles data on laboratory-confirmed foodborne illness cases from Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, and Tennessee, plus parts of California, Colorado, and New York. The system's coverage area includes 45 million people, or about 15% of the US population.

Total cases increased
A total of 17,883 foodborne infections were reported in 2007, up slightly from the 17,252 reported in 2006, according to the full FoodNet report published today in Morbidity and Mortality Weekly Report.

Salmonella led the list, with 6,790 confirmed cases (38% of the total), or 14.92 cases per 100,000 population. Case totals and rates per 100,000 population for the other pathogens were: Campylobacter, 5,818, 12.79; Shigella, 2,848, 6.26; Cryptosporidium, 1,216, 2.67; E coli O157:H7, 545, 1.20; Shiga toxin–producing E coli (STEC) non-O157:H7, 260, 0.57; Yersinia, 163, 0.36; Listeria, 122, 0.27; Vibrio, 108, 0.24; and Cyclospora, 13, 0.03.

In addition, FoodNet identified 82 cases of hemolytic uremic syndrome (HUS), a type of kidney failure associated with E coli infections, in children (younger than 18 years), for a rate of 0.78 cases per 100,000 children. Fifty-eight of the 82 cases were in children under age 5, for a population rate of 2.01 per 100,000.

"E coli O157 actually reached a low point in 2003 and 2004 and then increased again in 2005 and 2006," Tauxe said at the news conference. "Now it's 1.2 per 100,000, and that's a bit lower than 2006, but if you compare that to the 3 previous years, the difference is not a significant one." He noted that 2006 was marked by E coli outbreaks linked to fresh spinach and shredded lettuce, and 2007 saw an increased in ground beef recalls related to E coli.

Specifically, E coli triggered 21 ground beef recalls last year, 10 of which were linked to illnesses, according to the MMWR report. The recalls prompted the US Department of Agriculture (USDA) to launch some new initiatives last fall and to hold a public meeting in Washington this week to review the situation.

The increase in Cryptosporidium cases may reflect increased diagnostic testing triggered by the licensing of a new treatment, nitazoxanide, the CDC reported. Said Tauxe, "There wasn't a compelling reason to get a test done in the past. Now it's something they [physicians] can treat."

Battling Salmonella
The federal government has set specific targets for reducing rates of four foodborne infections by 2010. Of those, the Salmonella level is furthest from the target, with a 2007 incidence of 14.92 cases per 100,000, more than twice the target of 6.8 per 100,000, the CDC says.

Salmonella live in the intestines of most food animals and can infect humans by various routes, including food from animal sources, raw produce contaminated with animal waste, and contaminated water, the MMWR report notes. In 2007, salmonellosis outbreaks were linked to contaminated peanut butter, frozen pot pies, and a puffed vegetable snack.

The USDA launched an initiative to improve control of Salmonella in 2006 and added more efforts this year, the report notes. In the USDA's Salmonella testing program, the proportion of broiler chickens that had Salmonella dropped from 16.3% in 2005 to 11.4% in 2006 and 8.5% in 2007, it says.

Craig Hedberg, a foodborne disease epidemiologist and associate professor of occupational and environmental health at the University of Minnesota in Minneapolis, said Salmonella seems to be the toughest foodborne pathogen to address.

"If you compare where we are with the various diseases in relation to the national objectives, the one we clearly have the biggest problem with is Salmonella," he said. "We haven't really started to close the gap at all with Salmonella. That probably reflects the range of animal reservoirs that exist for Salmonella and the multiple transmission pathways that occur."

Hedberg said Salmonella was the main target of the "hazard analysis/critical control point" (HACCP) program launched by the USDA for the meat and poultry industry in the 1990s, and yet the overall rates of Salmonella infections have changed little. "That doesn't mean that the pathogen reduction programs have failed, but it probably means the epidemiology of this disease is much more complex than would be implied by our focus on the primary food animals as the source of exposure," he added.

In addition to contaminated food from animal sources, other routes of Salmonella infection that deserve attention include contaminated produce, contaminated drinking water, and infected restaurant workers, Hedberg said.

Regional variability
In other comments on the CDC report, Hedberg observed that the case rates for some of the foodborne pathogens vary widely by state or region, a fact that he said warrants more attention. For example, the incidence of Campylobacter ranged from fewer than 8 cases per 100,000 in Georgia, Tennessee, and Maryland to more than 28 cases per 100,000 in California.

"You see this pattern where the highest rates are in the western part of the country and the lowest rates are in the southeastern US," he said. "It's not clear why that would be, particularly since we so strongly associate Campylobacter with chicken, and the southeastern US is a big chicken-producing and chicken-consuming area. I don't know what the implications of that are, but when we start looking at the idea of developing new [disease-prevention] strategies, part of those strategies really need to focus on what the regional patterns of disease and risk are."

CDC. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food—10 states, 2007. MMWR 2008 Apr 11;57(14):366-70 [Full text]

See also:

Apr 12, 2007, CIDRAP News story "CDC says some foodborne illnesses rose in 2006"

2006 FoodNet report in MMWR

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