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

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.

2004 Surveillance

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).

Comparison of 2004 Data with 1996--1998

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.

Editorial Note:

During 1996--2004, substantial declines occurred in the estimated incidence of infections with Campylobacter, Cryptosporidium, STEC O157, Listeria, S. Typhimurium, and Yersinia. The 2004 incidence of STEC O157 infections declined below the 2010 national target of 1.0 case per 100,000 persons in FoodNet overall and in seven of the 10 surveillance sites. In addition, the decline in Campylobacter incidence represents progress toward the national health objective of 12.3 cases per 100,000 persons (3); the renewed decline in Listeria incidence, to 2.7 cases per 1 million population in 2004, suggests that the revised national objective to reduce foodborne listeriosis to 2.5 cases per 1 million population by 2005 might be achievable with continued efforts (4).

The declines described in this report have occurred concurrently with several important food safety initiatives and education efforts (1). The substantial decline of STEC O157 infections first noted in 2003 and sustained in 2004 is consistent with declines in STEC O157 contamination of ground beef reported by the U.S. Department of Agriculture Food Safety and Inspection Service (FSIS) for 2003 (6) and 2004 (http://www.fsis.usda.gov/news_&_events/NR_022805_01/index.asp). Multiple interventions might have contributed to this decline, including industry response to the FSIS 2002 notice to manufacturers to reassess control strategies for STEC O157 in the production of ground beef and enhanced strategies for reduction of pathogens in live cattle and during slaughter (6). The overall decline in Campylobacter incidence from the baseline period to 2004, the majority of which occurred before 2001, might reflect efforts to reduce contamination of poultry and educate consumers about safe food-handling practices. Although the incidence of Listeria infections decreased from the period 1996--1998 through 2004, the incidence in 2004 was comparable to 2002, after an increase in 2003 (Figure 1); efforts must continue to prevent foodborne listeriosis.

The decline in Salmonella incidence was modest compared with those of other foodborne bacterial pathogens. Only one of the five most common Salmonella serotypes, S. Typhimurium, declined 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 multistate tomato-associated S. Javiana outbreak that occurred in the summer of 2004 emphasizes the need to better understand Salmonella reservoirs and contamination of produce during production and harvest (5). The Food and Drug Administration recently developed a plan to decrease foodborne illness associated with fresh produce (7). Moreover, multidrug resistance is an emerging problem among Salmonella serotypes, particularly S. Newport; large multistate outbreaks associated with ground beef are cause for increased concern (8).

The findings in this report are subject to at least five limitations. First, FoodNet relies on laboratory diagnoses, and many foodborne illnesses are not laboratory diagnosed. For example, infections such as norovirus are not identified routinely in clinical laboratories. Second, protocols for isolation of enteric pathogens (e.g., non-O157 STEC) in clinical laboratories vary and are not implemented uniformly within FoodNet sites (9). Third, reported illnesses might have been acquired through nonfoodborne sources; reported incidence rates do not represent foodborne sources exclusively. Fourth, although the FoodNet population is similar to the U.S. population (2), the findings might not be generalizable to the entire population of the United States. Finally, year-to-year changes in incidence might reflect either annual variations or sustained trends.

Enhanced efforts are needed across the farm-to-table continuum to understand and control pathogens in animals and plants, to reduce or prevent contamination during processing, and to educate consumers about risks and prevention measures. Such efforts can be particularly focused when an animal reservoir species and transmission route for a pathogen are known. For example, many Vibrio infections are related to consumption of raw molluscan shellfish harvested from waters where Vibrio are present; ultra-high hydrostatic pressure treatment of oysters will likely prevent Vibrio infections. Other effective prevention measures, such as pasteurization of in-shell eggs and irradiation of ground meat and raw poultry, should be used more widely, particularly for foods eaten by persons at high risk. Consumers should follow safe food-handling recommendations and not consume raw or undercooked shellfish, eggs, ground beef, or poultry. In addition, efforts are needed to prevent transmission by nonfoodborne routes (e.g., via water, person-to-person, and exposure to animals or their environments). Guidelines to prevent disease associated with direct contact with animals or their environments in public settings (e.g., fairs and petting zoos) have recently been published (10).

References

  1. Allos BM, Moore MR, Griffin PM, Tauxe RV. Surveillance for sporadic foodborne disease in the 21st century: the FoodNet perspective. Clin Infect Dis 2004;38(Suppl 3):S115--20.
  2. Hardnett FP, Hoekstra RM, Kennedy M, Charles L, Angulo FJ; Emerging Infections Program FoodNet Working Group. Epidemiologic issues in study design and data analysis related to FoodNet activities. Clin Infect Dis 2004;38(Suppl 3):S121--6.
  3. US Department of Health and Human Services. Healthy people 2010 (conference ed, in 2 vols). Washington, DC: US Department of Health and Human Services; 2000.
  4. US Department of Agriculture, Food Safety and Inspection Service. 9 CFR Part 430. Control of Listeria monocytogenes in ready-to-eat meat and poultry products; final rule. Federal Register 2003;68:34,208--54.
  5. CDC. Outbreaks of Salmonella infections associated with eating Roma tomatoes---United States and Canada, 2004. MMWR 2005;54:325--8.
  6. Naugle AL, Holt KG, Levine P, Eckel R. 2005. Food Safety and Inspection Service regulatory testing program for Escherichia coli O157:H7 in raw ground beef. J Food Prot 2005;68:462--8.
  7. Food and Drug Administration. Produce safety from production to consumption: 2004 action plan to minimize foodborne illness associated with fresh produce consumption. Rockville, MD: US Department of Health and Human Services, Food and Drug Administration; 2004. Available at http://www.cfsan.fda.gov/~dms/prodpla2.html.
  8. CDC. Outbreak of multidrug-resistant Salmonella Newport---United States, January--April 2002. MMWR 2002;51:545--8.
  9. Voetsch AC, Angulo FJ, Rabatsky-Ehr T, et al. 2004. Laboratory practices for stool-specimen culture for bacterial pathogens, including Escherichia coli O157:H7, in the FoodNet sites, 1995--2000. Clin Infect Dis 2004;38(Suppl 3):S190--7.
  10. CDC. Compendium of measures to prevent disease associated with animals in public settings, 2005: National Association of State Public Health Veterinarians, Inc. (NASPHV). MMWR 2005;54(No. RR-4).

* Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.


Figure 1

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Figure 2

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Table

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