CDC cites declines in major foodborne infections

Robert Roos

Apr 15, 2005 (CIDRAP News) The federal government yesterday announced reductions in the rates of several common foodborne bacterial infections in 2004, especially the potentially life-threatening Escherichia coli O157:H7.

The rate of E coli cases dropped to just below 1 per 100,000 people, thereby fulfilling one of the government's "Healthy People 2010" goals for the first time, the Centers for Disease Control and Prevention (CDC) and other agencies announced.

E coli and several other foodborne infections showed sizable declines in comparison with a baseline period of 1996 through 1998, the CDC reported in Morbidity and Mortality Weekly Report. E coli cases were down 42%, Campylobacter cases 31%, Cryptosporidium cases 40%, Yersinia cases 45%, and Salmonella cases 8%.

Federal officials attributed much of the good news to regulatory efforts of the past few years. "Our efforts are working and we're making progress in reducing foodborne illness," CDC Director Dr. Julie Gerberding said in a news release.

Agriculture Secretary Mike Johanns added in the same release, "The continued reduction in illnesses from E coli O157 is a tremendous success story and we are committed to continuing this positive trend in the future."

On the down side, only one of the five most common strains of Salmonella actually declined in 2004, and Salmonella contamination of produce has puzzled investigators, the CDC said. Also, Vibrio infections, usually associated with raw shellfish, increased, while some other foodborne infections have changed little in recent years.

The CDC data come from the Foodborne Diseases Active Surveillance Network, or FoodNet, which now covers about 15% of the US populationabout 44 million people. The network includes all or parts of 10 states (California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, and Tennessee). It collects data on all laboratory-confirmed cases of common foodborne illnesses.

FoodNet counted a total of 15,806 illness cases caused by nine pathogens in 2004, compared with 15,600 cases in 2003 (when the network covered about 3 million fewer people). The case numbers and incidence rates for the most common illnesses in 2004 and 2003 were as follows:

2004

2003

Pathogen

Total cases

Incidence

Total cases

Incidence

Salmonella*

6,464

14.7

6,017

14.5

Campylobacter*

5,665

12.9

5,215

12.6

Shigella*

2,231

5.1

3,021

7.3

Cryptosporidium

613

13.2

480

10.9

E coli O157:H7*

401

0.9

443

1.1

Yersinia

173

3.9

161

4.0

Vibrio

124

2.8

110

3.0

Listeria

120

2.7

138

3.3

*Incidence is in cases per 100,000 population.
Incidence is in cases per 1 million population.

Because the areas and populations included in FoodNet have increased since the network was launched in 1996, the CDC used a statistical model to estimate the long-term changes in rates of foodborne infections. This year the agency compared 2004 rates with overall rates for the 1996-98 baseline period.

The reduction in E coli cases parallels a decline in E coli contamination in ground beef samples tested by the US Department of Agriculture (USDA). The proportion of contaminated samples was 43% lower in 2004 than in 2003, according to the USDA.

USDA attributes that improvement to regulatory changes launched in 2002, when the agency ordered beef plants to reassess their food safety systems and take specific steps to prevent E coli contamination. Most plants have made major changes in their operations since then, and many have increased their testing for E coli, the USDA said in a news release yesterday.

While the overall rate of E coli cases dropped, the rate varied considerably from state to state. Most states had a rate below 1 case per 100,000, but Minnesota and Oregon had rates of 2.2 and 1.7 per 100,000, respectively. Maryland had the lowest rate at 0.4 case per 100,000.

Foodborne disease expert Craig Hedberg, PhD, said he views the E coli data as "probably real and relevant." Commenting by e-mail, he told CIDRAP News, "I think the overall rates showing declines in the incidence of O157 for 2003 and 2004 are consistent with the USDA sampling data (and consistent with industry data as well)." Hedberg is an associate professor in environmental health sciences at the University of Minnesota's School of Public Health.

But Hedberg added that the now-fulfilled "Healthy People 2010" goal for E coli cases "is not an endpoint. One case per 100,000 translates to 2,500 to 3,000 cases per year. Thus, there is still plenty of room to argue for the need to use irradiation of our ground beef supply."

He said the variability in rates across the country could reflect the more rural nature of states like Minnesota and Oregon, with a potential for environmental transmission of E coli.

Not all of the foodborne infections have declined. By the CDC's trend-spotting statistical test, Shigella cases haven't changed significantly, and Vibrio cases have increased 47%. And while the incidence of Listeria cases dropped from the baseline period through 2004, the 2004 rate was about the same as in 2002, the report says.

In addition, only one of the five most common Salmonella strainsS Typhimuriumdropped significantly. "To achieve the national health objective of reducing the number of cases to 6.8 per 100,000 persons, greater efforts are needed to understand the complex epidemiology of Salmonella and to identify effective pathogen-reduction strategies," the CDC says. This was illustrated by last year's multistate outbreak of salmonellosis linked with Roma tomatoes, in which the source of the contamination remains a mystery.

In a news briefing yesterday, Dr. Robert Brackett, director of the Food and Drug Administration's Center for Food Safety and Applied Nutrition, said the FDA intends to propose a plan later this year for reducing Vibrio infections, after consulting with the seafood industry. He added that those cases can be prevented by cooking seafood thoroughly.

Aside from the decline in E coli cases, Hedberg voiced some wariness about the trends reported by the CDC. "With respect to the other 'trends,' I don't think we really know enough, either whether they are stable trends . . . or to what they may be attributed," he commented. "It remains very curious to me that Salmonella has been the target of the USDA's pathogen-reduction plans, and yet we've not reduced Salmonella to any great extent." He said one possibility is that measures for keeping Salmonella out of meat are working, but more people are getting sick from Salmonella in other foods.

CDC. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food10 sites, United States, 2004. MMWR 2005 Apr 15;54(14):352-6 [Full text]