Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food - 10 Sites, United States, 2004

Morbidity and Mortality Weekly Report. 2005;54(14):352-356. 

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Foodborne illnesses are a substantial health burden in the United States.[1] The Foodborne Diseases Active Surveillance Network (FoodNet) of CDC's Emerging Infections Program collects data from 10 U.S. sites* on diseases caused by enteric pathogens transmitted commonly through food. FoodNet quantifies and monitors the incidence of these infections by conducting active, population-based surveillance for laboratory-diagnosed illness.[2] This report describes preliminary surveillance data for 2004 and compares them with baseline data from the period 1996-1998. The 2004 data indicate declines in the incidence of infections caused by Campylobacter , Cryptosporidium , Shiga toxin-producing Escherichia coli (STEC) O157, Listeria , Salmonella , and Yersinia . Declines in Campylobacter and Listeria incidence are approaching national health objectives (objectives 10-1a through 1d); for the first time, the incidence of STEC O157 infections in FoodNet is below the 2010 target[3,4] ( Table ). However, further efforts are needed to sustain these declines and to improve prevention of foodborne infections; efforts should be enhanced to reduce pathogens in food animal reservoirs and to prevent contamination of produce.

In 1996, FoodNet began active, population-based surveillance for laboratory-diagnosed cases of Campylobacter , STEC O157, Listeria , Salmonella , Shigella , Vibrio , and Yersinia . In 1997, FoodNet added surveillance for cases of Cryptosporidium , Cyclospora , and hemolytic uremic syndrome (HUS). In 2000, FoodNet began collecting information on non-O157 STEC. In 2004, FoodNet began determining whether a case was part of a national foodborne disease outbreak reported to CDC via the electronic Foodborne Outbreak Reporting System (eFORS).

FoodNet personnel ascertain cases through contact with all clinical laboratories in their surveillance areas. HUS surveillance is conducted through a network of pediatric nephrologists and infection-control practitioners, and the review of records of hospitalized patients. Because of the time required for review of hospital records, this report contains preliminary 2003 HUS data.

During 1996-2004, the FoodNet surveillance population increased from 14.2 million persons in five sites to 44.1 million persons (15.2% of the U.S. population) in 10 sites. Preliminary incidence for 2004 was calculated by using the number of laboratory-confirmed infections and dividing by 2003 population estimates. Final incidence for 2004 will be reported (at http://www.cdc.gov/foodnet ) when 2004 population estimates are available from the U.S. Census Bureau.

In 2004, a total of 15,806 laboratory-diagnosed cases of infections in FoodNet surveillance areas were identified, as follows: Salmonella , 6,464; Campylobacter , 5,665; Shigella , 2,231; Cryptosporidium , 613; STEC O157, 401; Yersinia , 173; Vibrio , 124; Listeria , 120; and Cyclospora, 15. Overall incidence per 100,000 persons was 14.7 for Salmonella, 12.9 for Campylobacter, 5.1 for Shigella, and 0.9 for STEC   O157. The overall incidence per 1 million persons was 13.2 for Cryptosporidium, 3.9 for Yersinia, 2.8 for Vibrio, 2.7 for Listeria, and 0.3 for Cyclospora. However, substantial variation occurred across surveillance sites ( Table ).

Of the 5,942 (92%) Salmonella isolates serotyped, five serotypes accounted for 56% of infections, as follows: Typhimurium, 1,170 (20%); Enteritidis, 865 (15%); Newport, 585 (10%); Javiana, 406 (7%); and Heidelberg, 304 (5%). Among 112 (90%) Vibrio isolates identified to species, 58 (52%) were V. parahaemolyticus, and 16 (14%) were V. vulnificus . FoodNet also collected data on 106 non-O157 STEC infections. An O antigen was determined for 80 (75%) of the non-O157 STEC isolates, including O111, 40 (50%); O103, 14 (18%); and O26, 10 (13%). In 2003, FoodNet collected data on 52 HUS cases in persons aged <15 years (rate: 0.6 per 100,000 persons aged <15 years); 36 (69%) of the 52 HUS cases occurred in children aged <5 years (rate: 1.3 per 100,000 children aged <5 years).

In 2004, FoodNet cases were part of 239 nationally reported foodborne disease outbreaks (defined as two or more illnesses from a common source); 138 (58%) of these outbreaks were associated with restaurants. An etiology was reported in 152 (64%) outbreaks. The most common etiologies were norovirus (57%) and Salmonella (18%). Cases associated with outbreaks influenced the incidence of laboratory-diagnosed infections. For example, the incidence of S . Javiana cases increased substantially in 2004, in part because of a multistate outbreak associated with Roma tomatoes[5] that included 42 laboratory-diagnosed cases in Maryland (CDC, unpublished data, 2005).

To account for the increase in the number of FoodNet sites and populations under surveillance since 1996 and for variation in the incidence of infections among sites, a main-effects, log-linear Poisson regression model (negative binomial) was used to estimate statistically significant changes in the incidence of pathogens.[2] To create a baseline period, an average annual incidence for the first 3 years (2 years for Cryptosporidium ) of FoodNet surveillance, 1996-1998, was calculated. Next, the estimated change in incidence (relative rate) between the baseline period and 2004 was calculated, along with a 95% confidence interval (CI). The 3-year baseline, which differs from the 1996 baseline used in previous reports, resulted in more stable and precise relative rate estimates.

Comparing 1996-1998 with 2004, the estimated incidence of several infections declined significantly, as illustrated by the relative rates (Figure 1). The estimated incidence of infection with Campylobacter decreased 31% (95% CI = 25%-36%), Cryptosporidium decreased 40% (CI = 26%-52%), STEC O157 decreased 42% (CI = 28%-54%), Listeria decreased 40% (CI = 25%-52%), Yersinia decreased 45% (CI = 32%-55%), and overall Salmonella infections decreased 8% (CI = 1%-15%). The estimated incidence of Shigella infections did not change significantly in 2004 compared with the baseline period. Overall Vibrio infections increased 47% (CI = 7%-102%) (Figure 1); this increase was less than that reported previously because of the increased stability of the baseline rate estimate.

Although Salmonella incidence decreased overall, of the five most common Salmonella serotypes, only the incidence of S . Typhimurium decreased significantly (41% [CI = 34%-48%]), as illustrated by the relative rates comparing 2004 with the 1996-1998 baseline period (Figure 2). Estimated incidence of S . Enteritidis and S . Heidelberg did not change significantly; incidence of S . Newport and S . Javiana increased 41% (CI = 5%-89%) and 167% (CI = 75%-306%), respectively.

Reported by:   D Vugia, MD, California Dept of Health Svcs. A Cronquist, MPH, Colorado Dept of Public Health and Environment. J Hadler, MD, Connecticut Dept of Public Health. M Tobin-D'Angelo, MD, Div of Public Health, Georgia Dept of Human Resources. D Blythe, MD, Maryland Dept of Health and Mental Hygiene. K Smith, DVM, Minnesota Dept of Health. K Thornton, MD, Institute for Public Health, Univ of New Mexico Health Sciences Center, Albuquerque. D Morse, MD, New York State Dept of Health. P Cieslak, MD, Oregon Dept of Human Svcs. T Jones, MD, Tennessee Dept of Health. R Varghese, MD, Office of Public Health Science, Food Safety and Inspection Svc, US Dept of Agriculture. J Guzewich, MPH, Center for Food Safety and Applied Nutrition, Food and Drug Admin. F Angulo, DVM, P Griffin, MD, R Tauxe, MD, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; J Dunn, DVM, EIS Officer, CDC.

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