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Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food --- 10 States, 2008
Foodborne diseases remain an important public health problem in the United States. The Foodborne Diseases Active Surveillance Network (FoodNet) of CDC's Emerging Infections Program collects data from 10 U.S. states* on diseases caused by enteric pathogens transmitted commonly through food. FoodNet is an active, population-based surveillance system for these laboratory-confirmed infections (1). This report describes preliminary surveillance data for 2008 and trends since 1996. In 2008, the estimated incidence of infections caused by Campylobacter, Cryptosporidium, Cyclospora, Listeria, Shiga toxin-producing Escherichia coli (STEC) O157, Salmonella, Shigella, Vibrio, and Yersinia did not change significantly when compared with the preceding 3 years. For most infections, incidence was highest among children aged <4 years, whereas the percentage of persons hospitalized and the case fatality rate were highest among persons aged >50 years. None of the Healthy People 2010 targets for reduction of foodborne pathogens (objective 10-1) (2) were reached in 2008. The lack of recent progress points to gaps in the current food safety system and the need to continue to develop and evaluate food safety practices as food moves from the farm to the table.
FoodNet has conducted active, population-based surveillance for laboratory-confirmed cases of infection caused by Campylobacter, Listeria, Salmonella, STEC O157, Shigella, Vibrio, and Yersinia since 1996, Cryptosporidium and Cyclospora since 1997, and STEC non-O157 since 2000 in 10 participating states. FoodNet personnel actively contact clinical laboratories (on a regular basis, depending on the size of the laboratory) to ascertain laboratory-confirmed cases of infection occurring within the surveillance area (1). In 2004, FoodNet began collecting data regarding which laboratory-confirmed infections were associated with outbreaks of Salmonella and STEC O157. FoodNet also conducts surveillance for hemolytic uremic syndrome (HUS), a complication of STEC infection characterized by renal failure and microangiopathic hemolytic anemia, through a network of pediatric nephrologists and infection-control practitioners, and validates diagnoses through reviews of hospital discharge data. Because of the time required to review hospital records, this report contains preliminary HUS data for 2007, the most recent data available (1).
Preliminary incidence rates for 2008 were calculated by dividing the number of laboratory-confirmed infections by U.S. Census Bureau population estimates for 2007. The FoodNet surveillance population was approximately 46 million persons (15% of the U.S. population) in 2007. Final incidence rates will be reported when population estimates for 2008 are available.
In 2008, a total of 18,499 laboratory-confirmed cases of infection in FoodNet surveillance areas were identified. The number of infections and incidence per 100,000 population were reported as follows: Salmonella (7,444; 16.20), Campylobacter (5,825; 12.68), Shigella (3,029; 6.59), Cryptosporidium (1,036; 2.25), STEC O157 (513; 1.12), STEC non-O157 (205; 0.45), Yersinia (164; 0.36), Listeria (135; 0.29), Vibrio (131; 0.29), and Cyclospora (17; 0.04). Substantial variation in incidence rates occurred among surveillance areas (Table 1). Among all age groups (<4 years, 4--11 years, 12--19 years, 20--49 years, and >50 years), the highest incidence occurred among children aged <4 years for all infections except those caused by Cyclospora and Vibrio (Table 2).
Among age groups of persons infected with the following pathogens, the percentage of persons hospitalized was highest in persons aged >50 years: Listeria (86.2%), STEC O157 (53.3%), Vibrio (45.6%), Salmonella (40.0%), Yersinia (37.5%), Shigella (27.9%), Cryptosporidium (24.5%), and Campylobacter (20.5%). Among age groups of persons infected with the following pathogens, the case fatality rate (CFR) was highest in persons aged >50 years: Listeria (19.5%), Vibrio (7.4%), Salmonella (1.3%), Shigella (0.4%), and Campylobacter (0.4%). For infection with STEC O157, the CFR was highest among children aged <4 years (2.8%); for infection with Cryptosporidium and Yersinia, the CFR was highest in persons aged 20--49 years (1.3% and 3.0%, respectively).
Among 6,750 (91%) Salmonella isolates serotyped, 10 serotypes accounted for 73% of infections: Enteritidis, 1,356 (20.1%); Typhimurium, 1,077 (16.0%); Newport, 681 (10.1%); Javiana, 423 (6.3%); Saintpaul, 403 (6.0%); I 4,,12:i:-, 269 (4.0%); Muenchen, 213 (3.2%); Heidelberg, 198 (2.9%); Montevideo, 194 (2.9%); and Braenderup, 108 (1.6%). Among 131 (92%) Vibrio isolates for which the species was identified, 72 (55.0%) were parahaemolyticus, 19 (14.5%) were vulnificus, and eight (6.1%) were alginolyticus. Among 205 STEC non-O157 isolates tested for O antigen determination, 185 (90%) had an identifiable O antigen, most commonly O26 (28.1%), O103 (27.0%), or O111 (19.5%).
In 2007, FoodNet identified 77 cases of postdiarrheal HUS in persons aged <18 years (0.73 cases per 100,000 children). Among these 77 cases, 52 (68%) occurred in children aged <5 years (1.75 cases per 100,000 children).
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 2008 compared with previous years. This model accounts for site-to-site variation and the change in population in FoodNet surveillance areas over time (1). The average annual incidence for the preceding 3 years (2005--2007) and the first 3 years of surveillance (1996--1998) were used for comparison. The estimated change in incidence between 2008 and the comparison periods was calculated with 95% confidence intervals (CIs). For HUS surveillance, the average annual incidence for 2004--2006 was used as the comparison period. Changes over time were not analyzed for STEC non-O157, partly because changes in clinical laboratory practices, such as increases in Shiga toxin testing with enzyme immunoassay, likely affected reporting (3).
The estimated incidence of Campylobacter, Listeria, Salmonella, Shigella, STEC O157, Vibrio, Yersinia, and Cryptosporidium infections did not change significantly compared with the preceding 3 years (Figure 1). The apparent increase in Salmonella infections was not significant (CI = 0%--12%). Among the 10 most common Salmonella serotype infections, the incidence of Enteritidis increased 19% (CI = 3%--39%), Saintpaul increased 182% (CI = 112%--274%), and Heidelberg decreased 28% (CI = 12%--41%); the incidence of the other seven serotypes did not change significantly. Trends for Cyclospora infection were not calculated because of low incidence across sites and years. The estimated incidence of postdiarrheal HUS in children aged <5 years in 2007 did not change significantly compared with 2004--2006.
The lack of significant change in recent years is in contrast to trends from 1996, when FoodNet surveillance began, to 2004 (Figure 2). By 2008, in comparison with 1996--1998, modeled relative rates of infection with Yersinia had decreased 48% (CI = 35%--59%), Shigella had decreased 40% (CI = 15%--58%), Listeria had decreased 36% (CI = 20%--49%), Campylobacter had decreased 32% (CI = 27%--37%), and STEC O157 had decreased 25% (CI = 8%--39%), but Vibrio had increased 47% (CI = 9%--99%). The estimated incidence of infection with Cryptosporidium and Salmonella did not change significantly over this period.
Outbreak-Associated Cases of Infection
In 2008, outbreak-associated infections accounted for 132 (25.7%) of STEC O157 cases and 547 (7.4%) of Salmonella cases. Two large multistate outbreaks of Salmonella infections that included FoodNet sites were investigated in 2008: an outbreak of S. Saintpaul infections associated with imported produce (4) and an outbreak of S. Typhimurium infections associated with peanut butter and peanut butter--containing products (5).
Reported by: D Vugia, MD, California Dept of Public Health. A Cronquist, MPH, Colorado Dept of Public Health and Environment. M Cartter, 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. S Lathrop, PhD, New Mexico Dept of Health. D Morse, MD, New York State Dept of Health. P Cieslak, MD, Oregon Public Health Div. J Dunn, DVM, Tennessee Dept of Health. KG Holt, DVM, Food Safety and Inspection Svc, US Dept of Agriculture. Center for Food Safety and Applied Nutrition, Food and Drug Admin. OL Henao, PhD, RM Hoekstra, PhD, FJ Angulo, DVM, PM Griffin, MD, RV Tauxe, MD, Div of Foodborne, Bacterial, and Mycotic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases; KK Trivedi, MD, EIS Officer, CDC.
Despite numerous activities aimed at preventing foodborne human infections, including the initiation of new control measures after the identification of new vehicles of transmission (e.g., peanut butter--containing products), progress toward the national health objectives has plateaued, suggesting that fundamental problems with bacterial and parasitic contamination are not being resolved. Although significant declines in the incidence of certain pathogens have occurred since establishment of FoodNet, these all occurred before 2004. Of the four pathogens with current Healthy People 2010 targets, Salmonella, with an incidence rate of 16.2 cases per 100,000 in 2008, is farthest from its target for 2010 (6.8). The lack of recent progress toward the national health objective targets and the occurrence of large multistate outbreaks point to gaps in the current food safety system and the need to continue to develop and evaluate food safety practices as food moves from the farm to the table.
Efforts to reduce contamination of meat, poultry, produce, and other foods are ongoing. In 2006, the U.S. Department of Agriculture's Food Safety and Inspection Service implemented a Salmonella initiative program to prevent Salmonella contamination of meat and poultry.§ Industry response to the program has resulted in a decrease in the percent-positive rate for Salmonella in raw broiler chicken from 11.4% in 2006 to 7.3% in 2008 (6). Additionally, the percentage of broiler chicken slaughter establishments with Salmonella contamination rates at half or below half of the performance standard increased from 49% in 2006 to 82% in 2008 (2010 target is 90%) (6). However, the percentage of ground beef samples yielding STEC O157 increased from 0.24% in 2007 to 0.47% in 2008 (7); whether the increase was related to focused sampling of higher risk facilities or improved laboratory detection, or whether the microbial load was actually higher, is unknown. In August 2008, the Food and Drug Administration (FDA) published a rule allowing irradiation of fresh iceberg lettuce and fresh spinach to help protect consumers from Salmonella and STEC O157; FDA also piloted an advanced screening system to identify food safety threats at all U.S. borders.¶
Enhanced and food-specific measures are needed to 1) control or eliminate pathogens in domestic and imported food; 2) reduce or prevent contamination during growing, harvesting, and processing; and 3) continue the education of restaurant workers and consumers about risks and prevention measures. In particular, continued efforts are needed to understand how contamination of fresh produce and processed foods occurs and to develop and implement measures that reduce it. More outbreaks can be recognized and their causative foods identified with rapid and complete subtyping of pathogens and with rapid standardized interviews of ill persons and appropriately selected controls.
The reported incidence of Campylobacter, Salmonella, and STEC O157 infections varies substantially by site. For example, incidence of Campylobacter is highest in California, incidence of Salmonella is highest in New Mexico and Georgia, and incidence of STEC O157 is highest in Colorado. Previous FoodNet studies suggest that even after controlling for laboratory testing practices, site-to-site variation in disease incidence reflects regional differences in exposures, which might include the consumption of contaminated food or exposure through other routes of transmission (8,9).
The reported incidence of Campylobacter, Cryptosporidium, Listeria, Salmonella, Shigella, STEC O157, and Yersinia infections remains highest among children aged <4 years. For most pathogens under surveillance, persons aged >50 years are at greater risk than are other age groups for hospitalization and death, making aggressive diagnosis and treatment especially important in this age group.
The findings in this report are subject to at least four limitations. First, because FoodNet relies on laboratory diagnoses, changing laboratory practices might affect the reported incidence of some pathogens. For example, fewer laboratory-confirmed infections might be reported as a result of increased use of nonculture tests. Second, many foodborne illnesses (e.g., norovirus infection) are not reported to FoodNet because these pathogens are not identified routinely in clinical laboratories. Third, differences in health-care seeking behaviors between age groups might contribute to a much higher incidence of reported illness in certain age groups (e.g., young children and older persons) (10). Finally, although the FoodNet population is similar demographically to the U.S. population, the findings might not be generalizable (1).
Consumers can reduce their risk for foodborne illness by following safe food-handling and preparation recommendations and by avoiding consumption of unpasteurized milk, raw or undercooked oysters, or other raw or undercooked foods of animal origin such as eggs, ground beef, and poultry. Risk also can be decreased by choosing pasteurized eggs, high pressure-treated oysters, and irradiated produce. Everyone should wash hands before and after contact with raw meat, raw foods derived from animal products, and animals and their environments. More detailed information on food safety practices is available at http://www.foodsafety.gov and http://www.fightbac.org.
* Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.
Age groups correspond to those defined by CDC's Healthy People in Every Stage of Life goals. Available at http://www.cdc.gov/osi/goals/people.html.
§ Additional information about the Salmonella verification sampling program is available at http://www.fsis.usda.gov/oppde/rdad/frpubs/04-026n.pdf.
¶ Additional information about the FDA Food Protection Plan is available at http://www.fda.gov/oc/initiatives/advance/food/progressreport1108.html.
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Date last reviewed: 4/8/2009