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Despite What Seems Like an Outbreak a Week, Preliminary FoodNet Data from 2007 on the Incidence of Infection with Pathogens Transmitted Commonly Through Food, Seems to Hold Relativey Steady

The CDC reported today:

The Foodborne Diseases Active Surveillance Network (FoodNet) of CDC’s Emerging Infections Program collects data from 10 U.S. states regarding diseases caused by pathogens commonly transmitted through food. FoodNet quantifies and monitors the incidence of these infections by conducting active, population-based surveillance for laboratory-confirmed infections. This report describes preliminary surveillance data for 2007 and compares them with data for previous years. In 2007, the estimated incidence of infections caused by Campylobacter, Listeria, Shiga toxin-producing Escherichia coli O157 (STEC O157), Salmonella, Shigella, Vibrio, and Yersinia did not change significantly, and Cryptosporidium infections increased compared with 2004–2006. Progress toward the targets for Healthy People 2010 national health objectives and targets regarding the incidence of foodborne infections occurred before 2004; however, none of the targets were reached in 2007. Salmonella incidence was the furthest from its national health target, suggesting that reaching this target will require new approaches.

Surveillance Methods

In 1996, FoodNet began active, population-based surveillance for laboratory-confirmed cases of infection caused by Campylobacter, Listeria, Salmonella, STEC O157, Shigella, Vibrio, and Yersinia. FoodNet added surveillance for cases of Cryptosporidium and Cyclospora infection in 1997 and STEC non-O157 infection in 2000. In 2004, FoodNet began collecting data regarding which laboratory-confirmed infections were associated with outbreaks.

Infection with STEC O157 can cause hemolytic uremic syndrome (HUS), a complication in which the kidneys fail. HUS surveillance, which began in 2000, is conducted in nine states through a network of pediatric nephrologists and infection-control practitioners and validated through review of hospital discharge data. Because of the time required for review of hospital records, this report contains preliminary HUS data for 2006.

During 1996–2007, the FoodNet surveillance population increased from 14.3 million persons (5% of the U.S. population) in five states to 45.5 million persons (15% of the U.S. population) in 10 states. The preliminary incidence for 2007 was calculated by dividing the number of laboratory-confirmed infections by population estimates for 2006. Final incidence will be reported when population estimates for 2007 are available from the U.S. Census Bureau. In previous years, final incidence has been comparable to preliminary incidence.

Surveillance Data

In 2007, a total of 17,883 laboratory-confirmed cases of infection in FoodNet surveillance areas were identified. The number of cases and incidence per 100,000 population were reported as follows: Salmonella (6,790; 14.92), Campylobacter (5,818; 12.79), Shigella (2,848; 6.26), Cryptosporidium (1,216; 2.67), STEC O157 (545; 1.20), STEC non-O157 (260; 0.57), Yersinia (163; 0.36), Listeria (122; 0.27), Vibrio (108; 0.24), and Cyclospora (13; 0.03). Substantial variation occurred across surveillance sites (Table). The highest incidence per 100,000 population for Salmonella (62.11), Shigella (27.77), Campylobacter (24.01), and STEC O157 (3.66) infections was among children aged <5 years. In 2006, FoodNet identified 82 cases of postdiarrheal HUS in persons aged <18 years (0.78 cases per 100,000 children); 58 (0.7%) cases occurred in children aged <5 years (2.01 cases per 100,000 children).

Of the 6,299 (92.8%) Salmonella isolates serotyped, seven serotypes accounted for 61.6% of infections: Enteritidis, 1,062 (16.9%); Typhimurium, 1,006 (16.0%); Newport, 656 (10.4%); I 4,[5],12:i:-, 358 (5.7%); Javiana, 347 (5.5%); Heidelberg, 243 (3.9%); and Montevideo, 211 (3.4%). Among 102 (94.4%) Vibrio isolates for which the species was identified, 59 (57.8%) were parahaemolyticus, 18 (17.7%) were alginolyticus, and 13 (12.8%) were vulnificus. Among 260 STEC non-O157 isolates tested for O antigen determination, 228 (87.7%) had an identifiable O antigen, primarily O26 (21.5%), O103 (20.6%), or O121 (19.3%).

Comparison with Previous Years

A main-effects, log-linear Poisson regression model (negative binomial) was used to estimate statistically significant changes in incidence of infections in 2007 compared with previous years. This model accounts for the increase in the surveillance population and for variations in incidence among sites. The average annual incidence for 2004–2006 and for 1996–1998 (1997–1998 for Cryptosporidium), the first years of surveillance, were used for comparison. The estimated change in incidence (relative rate) between 2007 and the comparison periods was calculated, along with 95% confidence intervals (CIs). For HUS surveillance, 2000–2001, the first years of surveillance, was used as the comparison period. Changes over time have not been analyzed for non-O157 STEC, partly because changes in clinical laboratory practices might have affected incidence reporting.

The estimated incidence of Campylobacter, Listeria, Salmonella, Shigella, STEC O157, Vibrio, and Yersinia infections (Figure 1) did not change significantly in 2007 compared with 2004–2006, but the estimated incidence of Cryptosporidium infections increased 44% (CI = 8%–91%). Among the seven most common Salmonella serotypes, the incidence of Typhimurium and Heidelberg decreased, I 4,[5],12:i- and Newport increased, and the others did not change significantly.

In comparison with 1996–1998, relative rates of Yersinia decreased 49% (CI = 36%–59%), Listeria decreased 42% (CI = 28%–54%), Shigella decreased 36% (CI = 9%–55%), Campylobacter decreased 31% (CI = 25%–36%), STEC O157 decreased 25% (CI = 9%–38%), and Salmonella decreased 8% (CI = 1%–14%) in 2007. The estimated incidence of infection with Cryptosporidium and Vibrio did not change significantly. The incidence of postdiarrheal HUS has paralleled that of STEC O157, declining in 2003 and 2004, followed by increases the next 2 years. The estimated incidence of postdiarrheal HUS in children aged <5 years in 2006 did not change significantly compared with 2000–2001.