Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food --- Selected Sites, United States, 2003
In the United States, an estimated 76 million persons contract foodborne and other acute diarrheal illnesses each year (1). CDC's Emerging Infections Program Foodborne Diseases Active Surveillance Network (FoodNet) collects data on diseases caused by enteric pathogens transmitted commonly through food in nine* U.S. sites (2). FoodNet quantifies and monitors the incidence of these infections by conducting active surveillance for laboratory-diagnosed illness (3). This report describes preliminary surveillance data for 2003 and compares them with 1996--2002 data. The data indicate substantial declines in the incidence of infections caused by Campylobacter, Cryptosporidium parvum, Escherichia coli O157, Salmonella, and Yersinia enterocolitica. These data represent progress toward meeting the 2010 national health objectives of reducing the incidence of foodborne infections (objective nos. 10.1a, 10.1b, and 10.1d) (4). However, increased efforts are needed to reduce further the incidence of foodborne illnesses, particularly among children.
In 1996, FoodNet began active surveillance for laboratory-diagnosed cases of Campylobacter, Shiga toxin--producing E. coli (STEC) O157, Listeria, Salmonella, Shigella, Vibrio, and Yersinia. In 1997, FoodNet added surveillance for cases of Cryptosporidium and Cyclospora cayetanensis. During 1996--2003, the FoodNet surveillance population increased from 14.2 million persons in five sites to 41.5 million in nine sites (14% of the U.S. population).
To ascertain cases, FoodNet personnel routinely contact all clinical laboratories in their surveillance areas. Preliminary incidence for 2003 was calculated by using the number of cases of diagnosed infections divided by 2002 population estimates (5).
In 2003, a total of 15,600 laboratory-diagnosed cases of infections under surveillance caused by nine pathogens were identified: 6,017, Salmonella; 5,215, Campylobacter; 3,021, Shigella; 480, Cryptosporidium; 443, E. coli O157; 161, Yersinia; 138, Listeria; 110, Vibrio; and 15, Cyclospora. Among the 5,455 (91%) Salmonella isolates serotyped, five serotypes accounted for 59% of infections: 1,104 (20%) Typhimurium, 759 (14%) Enteritidis, 653 (12%) Newport, 348 (6%) Heidelberg, and 331 (6%) Javiana. Among 2,810 (93%) Shigella isolates identified to species, 2,410 (86%) were S. sonnei, and 370 (13%) were S. flexneri. Among 100 (91%) Vibrio isolates identified to species, 46 (46%) were V. parahaemolyticus, and 16 (16%) were V. vulnificus.
As in previous years, certain infections affected children disproportionately. The incidence of Salmonella infection, defined as the number of laboratory isolations per 100,000 persons, was 122.7 for infants (i.e., aged <1 year) and 50.6 young children (i.e., aged 1--4 years), compared with 10.8 for other persons (i.e., aged >5 years). The incidence of Yersinia infection was 9.6 for infants and 1.4 for young children, compared with 0.2 for other persons. The incidence of E. coli O157 infection was 4.5 for young children, compared with 0.9 for other persons. Substantial variation in incidence across sites also was reported for most infections (Table).
For most pathogens, the 2003 incidence of infection was lower than the average annual incidence for 1996--1998 (Table). However, the number of sites and the population under surveillance have increased since FoodNet began in 1996, confounding this comparison. To account for the increased population and variation in the incidence among sites, a main effects log-linear Poisson regression model was used to estimate the effect of time on the incidence of the various pathogens by treating calendar year as a categorical variable. The relative change in incidence from 1996 to 2003 was estimated along with corresponding confidence intervals (CIs).
During 1996--2003, the estimated incidence of several infections declined significantly (Figure 1). The estimated incidence of Yersinia infections decreased 49% (95% CI = 61% to 34% decrease), E. coli O157 decreased 42% (95% CI = 58% to 19% decrease), Campylobacter decreased 28% (95% CI = 36% to 20% decrease), and Salmonella decreased 17% (95% CI = 26% to 7% decrease). From 1997 to 2003, the incidence of Cryptosporidium infection decreased 51% (95% CI = 64% to 34% decrease). The decrease in E. coli O157 infections occurred primarily during 2002--2003. Although the incidence of Cyclospora infection has decreased since 1997, the Poisson regression model could not be applied because of the small number of cases.
During 1996--2003, the estimated incidence of the most common Salmonella serotype, S. Typhimurium, decreased 38% (95% CI = 47% to 27% decrease). The incidence of the next most common serotypes, S. Enteritidis, S. Newport, and S. Heidelberg, showed considerable variation by year and did not change significantly. The incidence of S. Javiana increased 227% (95% CI = 66% to 546% increase) from 1996 to 2003; most of this increase occurred in Georgia.
The estimated incidence of Shigella and Listeria infections showed considerable variation by year and site and did not change significantly during 1996--2003 (Figure 2). Listeria did not continue to decline in 2003, as observed during the preceding 4 years. During 1996--2003, the incidence of Vibrio infections increased 116% (95% CI = 24% to 276% increase).
Reported by: D Vugia, MD, California Dept of Health Svcs. A Cronquist, MPH, Colorado Dept of Public Health and Environment. J Hadler, MD, Connecticut State Dept of Public Health. P Blake, 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. D Morse, MD, New York State Dept of Health. P Cieslak, MD, Oregon Dept of Human Svcs. T Jones, MD, Tennessee Dept of Health. D Goldman, MD, Office of Public Health Science, Food Safety and Inspection Svc, U.S. Dept of Agriculture. J Guzewich, MPH, Center for Food Safety and Applied Nutrition, Food and Drug Administration. F Angulo, DVM, P Griffin, MD, R Tauxe, MD, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; K Kretsinger, MD, EIS Officer, CDC.
During 1996--2003, the estimated incidence of Campylobacter, Cryptosporidium, E. coli O157, Salmonella, and Yersinia infections declined substantially. The decline in Campylobacter and E. coli O157 infections demonstrates that meeting the 2010 national health objectives of 12.3 and 1.0 per 100,000 persons, respectively (objective nos. 10.1a and 10.1b) is likely. Although the incidence of Salmonella infection has declined, it remains above its objective, and among the five most common Salmonella serotypes, only S. Typhimurium demonstrated a sustained decline in incidence.
The changes in the incidence of these infections occurred in the context of control measures implemented by government agencies and the food industry, enhanced food-safety education efforts, and increased attention by consumer groups and the media. In 1997, the U.S. Department of Agriculture (USDA)'s Food Safety and Inspection Service (FSIS) implemented the Pathogen Reduction/Hazard Analysis and Critical Control Point (HACCP) systems regulations in meat and poultry slaughter and processing plants. The decline of human E. coli O157 infections in 2003 follows an October 2002 FSIS notice to manufacturers of raw ground beef products that they must reassess their HACCP plans regarding this pathogen (6). Many beef processing plants do not distribute production lots of raw ground beef unless tests performed at the plant are negative for E. coli O157 (M. Koohmaraie, Meat Animal Research Center, USDA, personal communication, 2004). FSIS reported declines in the frequency of E. coli O157:H7 contamination of ground beef for 2003 (7). The decline in human Salmonella infections during 1996--2003 accompanies a decline in the isolation of Salmonella from meat and poultry by FSIS (8). The Food and Drug Administration has introduced additional interventions to prevent foodborne diseases. These include implementing HACCP regulations for the seafood industry beginning in 1997 and the juice industry beginning in 2002, publishing sprout safety guidance in 1999, publishing produce safety guidance in 1998, and implementing regulations requiring the refrigeration and safety labeling of shell eggs in 2001 (9).
During 1996--2003, no substantial changes were observed in the incidence of infection caused by Listeria, Shigella, and several common Salmonella serotypes (S. Enteritidis, S. Newport, and S. Heidelberg). The incidence of Vibrio and S. Javiana infections increased. Listeriosis might decline after full implementation of the national Listeria Action Plan (9). Future control measures should include mandatory, on-farm prevention efforts to reduce egg contamination with S. Enteritidis (10) and greater use of pasteurized eggs and irradiated ground meat. Additional targeted efforts should include further steps to reduce the prevalence of pathogens in the following animal reservoirs and the foods derived from them: broiler chickens and turkeys (Salmonella and Campylobacter); cattle and ground beef (Salmonella and E. coli O157); and seafood, particularly oysters (Vibrio). Efforts also should include steps to reduce contamination of fresh produce. The high incidence of several of these infections in infants and young children is of major concern. Further efforts are needed to determine risk factors for these infections and opportunities for prevention.
The findings in this report are subject to at least four limitations. First, although the majority of foodborne illnesses are not laboratory-diagnosed, FoodNet data are limited to laboratory-diagnosed illnesses, and are thus biased by factors that affect the probability of an illness being reported. Second, illnesses reported to FoodNet might be acquired through nonfoodborne sources (e.g., contaminated water, person-to-person contact, and direct animal exposure); reported incidences do not represent foodborne sources exclusively. Third, although FoodNet data provide the most detailed information available for these infections, the findings might not be generalizable to the entire U.S. population. Finally, year-to-year changes in incidence might reflect either annual variation or sustained trends; further data are needed to discern trends clearly.
The 2003 FoodNet final report, available in late 2004 at http://www.cdc.gov/foodnet, will include incidence figures and other information such as illness severity, hemolytic uremic syndrome, and non-O157 STEC isolations.
This report is based on data contributed by members of the Emerging Infections Program FoodNet Working Group.
* California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New York, Oregon, and Tennessee.
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