Foodborne bacterial disease rates dropped 23% from 1996 to 2001, CDC says

Apr 19, 2002 (CIDRAP News) – The incidence of seven common foodborne bacterial diseases dropped 23% between 1996 and 2001, at least in part because of new meat-processing safety rules and other federal food-safety efforts in the last few years, according to the Centers for Disease Control and Prevention (CDC).

"We think they [the figures] represent a real decrease in the actual numbers of these infections," said Robert Tauxe of the CDC in a telephone press briefing yesterday. He said the numbers indicate that "tens of thousands" fewer cases of illness occurred in 2001 than in 1996.

Tauxe and other officials attributed the improvement partly to the US Department of Agriculture's Hazard Analysis and Critical Control Point (HACCP) program for slaughterhouses and meat-processing plants. They also cited egg-safety programs and regulation of fruit and vegetable juices and seafood, among other measures.

The new findings from the Foodborne Diseases Active Surveillance Network (FoodNet) were published in the Apr 19 issue of Morbidity and Mortality Weekly Report. Foodnet surveillance covers nine states and portions of states, which include about 13% of the US population.

Rates of illness from the three leading foodborne pathogens—Salmonella, Campylobacter, and Shigella—all declined during the 5-year period. Infections with less common pathogens, including Yersinia enterocolitica and Listeria monocytogenes, also dropped. The rate of Escherichia coli O157 infections stayed roughly the same from 1996 through 2000 but dropped in 2001.

The FoodNet program began in 1996 with surveillance in Minnesota, Oregon, and selected counties in California, Connecticut, and Georgia. By 2001, the program also included Colorado, Maryland, New York, and Tennessee, bringing the total population base to 37.8 million. The program involves active surveillance for laboratory-diagnosed cases of infection with seven bacterial pathogens (Campylobacter, E coli O157, L monocytogenes, Salmonella, Shigella, Vibrio, and Y enterocolitica) and two parasites (Cryptosporidium parvum and Cyclospora cayetanensis). Hemolytic uremic syndrome (HUS), associated with E coli O157, also is monitored.

In 2001, Salmonella led the list of pathogens with 5,198 illness cases in the FoodNet territory, or 15.1 cases per 100,000 people. Campylobacter was second with 4,740 cases, or 13.8 per 100,000, while Shigella accounted for 2,201 cases, or 6.4 per 100,000. Cases per 100,000 population for the other pathogens were as follows: E coli O157, 1.6; Cryptosporidium, 1.5; Y enterocolitica, 0.4; Listeria, 0.3; Vibrio, 0.2; and Cyclospora, 0.1. The HUS rate was 0.9.

Yersinia had the biggest decline in incidence from 1996 to 2001 at 49% (95% confidence interval [CI], 35%-60%). The Listeria rate dropped 35% (95% CI, 9%-53%), as did that of Shigella (95% CI, 57% decrease to 3% increase), though the trend for Shigella was less consistent. Campylobacter rate decreased 27% (95% CI, 19%-35%) and Salmonella rate by 15% (95% CI, 7%-22%). The rate of E coli O157 changed little from 1996 to 2000, but in 2001 it dropped 21% relative to 1996 (95% CI, 41% decrease to 5% increase). The good news did not extend to Vibrio infections, the rate of which increased 97% between 1996 and 1997 and in 2001 was still 83% higher than in 1996.

Monitoring of the two parasitic infections began in 1997, according to the report. Cryptosporidium cases dropped 33% from 1997 to 2001; Cyclospora also declined, but cases were too few to permit a good percentage estimate.

Incidence rates varied widely from state to state. For example, Campylobacter rates ranged from 7.0 in Maryland to 31.7 in California, and Salmonella rates ranged from 8.2 in Oregon to 20.6 in Georgia. Because of the state-to-state variations and the increase in population under surveillance, the CDC used a regression model to estimate the overall changes in incidence rates.

"We do not think that these declines are related to a change in the way laboratories work or a change in the way the medical system works," said Tauxe. He said FoodNet surveys indicate that the rates at which people seek medical care and physicians get cultures have not changed.

Likely reasons for the decrease in foodborne illness, Tauxe said, include "a change in the way that food safety in animal slaughter and processing is managed. Beginning in 1997, the Department of Agriculture began implementing a new pathogen-reduction strategy for regulating meat and poultry slaughter and processing plants, and these declines in Yersinia, Listeria, Campylobacter, and Salmonella are happening at the same time that new strategy was being implemented."

The MMWR report cites the HACCP regulations first on the list of control measures that have probably helped reduce illness rates. However, it also notes that the prevalence of Salmonella in USDA-regulated products had declined even before the HACCP program was implemented. Other contributing factors cited by the CDC include Food and Drug Administration egg safety programs to prevent Salmonella Enteritidis, publication of good agricultural practices for fresh produce, HACCP regulation of fruit and vegetable juices and seafood, industry efforts including new technologies to reduce food contamination, food safety education, and increased regulation of imported food.

In reply to a question, Tauxe said, "I think the lack of a sustained decline in E coli O157 tells us that we really need to have increased efforts focused on this pathogen." He speculated that increased control measures may have decreased E coli O157 contamination in meat processing but that transmission of the germ may be increasing in other arenas.

Despite the improved figures, "the incidence of foodborne diseases remains high," the MMWR report says. In particular, the 2001 incidence rates for Campylobacter, E coli O157, Listeria, and Salmonella remain higher than the national goals for 2010 set by federal health officials. Goals have not been set for the other pathogens.

While the overall rate of salmonellosis declined, the report says, certain serotypes of Salmonella infection increased: S Newport, 32%; S Heidelberg, 34%; and S Javiana, 228%. Tauxe said Newport is now the third most common Salmonella serotype in the country, and its increase in humans parallels an increase in cattle.

The report also notes that some of the illnesses reported to FoodNet might be acquired through non-foodborne routes, such as contaminated water or interpersonal contact. Other limitations of the data include the fact that most foodborne illnesses are not laboratory-diagnosed or reported to state health departments and that FoodNet surveillance does not cover the whole country.

CDC. Preliminary FoodNet data on the incidence of foodborne illnesses—selected sites, United States, 2001. MMWR 2002(Apr 19);51(15):325-9

Full text

See also:

Transcript of CDC press briefing

Health and Human Services Department press release

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