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Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food --- 10 States, United States, 2005
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. states* regarding 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-confirmed illness (2). This report describes preliminary surveillance data for 2005 and compares them with baseline data from the period 1996--1998. Incidence of infections caused by Campylobacter, Listeria, Salmonella, Shiga toxin--producing Escherichia coli O157 (STEC O157), Shigella, and Yersinia has declined, and Campylobacter and Listeria incidence are approaching levels targeted by national health objectives (3) (Table). However, most of those declines occurred before 2005, and Vibrio infections have increased, indicating that further measures are needed to prevent foodborne illness.
In 1996, FoodNet began active, population-based surveillance for laboratory-confirmed cases of infection from Campylobacter, Listeria, Salmonella, STEC O157, Shigella, Vibrio, and Yersinia. In 1997, FoodNet added surveillance for cases of Cryptosporidium and Cyclospora infection. In 2000, FoodNet began collecting data on STEC non-O157 and comprehensive information on hemolytic uremic syndrome (HUS). 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. In addition, eight states review hospital discharge data to ascertain HUS cases. Because of the time required for review of hospital records, this report contains preliminary 2004 HUS data.
During 1996--2005, the FoodNet surveillance population increased from 14.2 million persons (5% of the U.S. population) in five states to 44.5 million persons (15% of the U.S. population) in 10 states. Preliminary incidence for 2005 was calculated using the number of laboratory-confirmed infections and dividing by 2004 population estimates. Final incidence for 2005 will be reported when 2005 population estimates are available from the U.S. Census Bureau.
In 2005, a total of 16,614 laboratory-confirmed cases of infections in FoodNet surveillance areas were identified, as follows: Salmonella (6,471 cases), Campylobacter (5,655), Shigella (2,078), Cryptosporidium (1,313), STEC O157 (473), Yersinia (159), STEC non-O157 (146), Listeria (135), Vibrio (119), and Cyclospora (65). Overall incidence per 100,000 population was 14.55 for Salmonella, 12.72 for Campylobacter, 4.67 for Shigella, 2.95 for Cryptosporidium, 1.06 for STEC O157, 0.36 for Yersinia, 0.33 for STEC non-O157, 0.30 for Listeria, 0.27 for Vibrio, and 0.15 for Cyclospora. Substantial variation occurred across surveillance sites (Table). In 2004, FoodNet identified 44 cases of HUS in children aged <15 years (rate: 0.49 per 100,000 children); 30 (68%) of these cases occurred in children aged <5 years (rate: 0.94).
Of the 5,869 (91%) Salmonella isolates serotyped, six serotypes accounted for 61% of infections, as follows: Typhimurium, 1,139 (19%); Enteritidis, 1,080 (18%); Newport, 560 (10%); Heidelberg, 367 (6%); Javiana, 304 (5%); and a monophasic serotype identified as Salmonella I 4,,12:i:-, 154 (3%). Among 109 (92%) Vibrio isolates identified to species level, 59 (54%) were V. parahaemolyticus, and 15 (14%) were V. vulnificus. FoodNet also collected data on 145 STEC non-O157 isolates that were tested for O-antigen determination; 117 (81%) had an identifiable O antigen, including O26 (37 [32%]), O103 (36 [31%]), and O111 (23 [20%]); 28 isolates did not react with the typing antisera used.
In 2005, FoodNet sites reported 205 foodborne disease outbreaks to the national Electronic Foodborne Outbreak Reporting System; 121 (59%) were associated with restaurants. Etiology was reported for 159 (78%) outbreaks; the most common etiologies were norovirus (49%) and Salmonella (18%).
Comparison of 2005 Data with 1996--1998
A main-effects, log-linear Poisson regression model (negative binomial) was used to estimate statistically significant changes in the incidence of pathogens. This model accounts for the increase in the number of FoodNet sites and its surveillance population since 1996 and for variation in the incidence of infections among sites (2). The average annual incidence for 1996--1998 (1997--1998 for Cryptosporidium), the first 3 years of FoodNet surveillance, was used as the baseline period. For HUS surveillance, 2000--2001 was used as the baseline. The estimated change in incidence (relative rate) between the baseline period and 2005 was calculated, along with a 95% confidence interval (CI).
The estimated annual incidence of several infections declined significantly from 1996--1998 to 2005 (Figure 1). The estimated incidence of infection with Yersinia decreased 49% (CI = 36%--59%), Shigella decreased 43% (CI = 18%--60%), Listeria decreased 32% (CI = 16%--45%), Campylobacter decreased 30% (CI = 25%--35%), STEC O157 decreased 29% (CI = 12%--42%), and Salmonella decreased 9% (CI = 2%--15%). Although Salmonella incidence decreased overall, of the five most common Salmonella serotypes, only the incidence of S. Typhimurium decreased significantly (42% [CI = 34%--48%]). The estimated incidence of S. Enteritidis increased 25% (CI = 1%--55%), S. Heidelberg increased 25% (CI = 1%--54%) and S. Javiana increased 82% (CI = 14%--191%). The estimated incidence of S. Newport increased compared with the baseline, but the increase was not statistically significant (Figure 2). The estimated incidence of postdiarrheal HUS in children aged <5 years decreased 45% in 2004 compared with 2000--2001; whether this trend is significant could not be determined, partly because the limited time span does not provide enough data to evaluate a Poisson regression model. The estimated incidence of Vibrio increased 41% (CI = 3%--92%) compared with the baseline, whereas the estimated incidence of Cryptosporidium infections did not change significantly.
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 State Public Health. T Jones, MD, Tennessee Dept of Health. K Holt, DVM, Food Safety and Inspection Svc, US Dept of Agriculture. J Guzewich, MPH, Center for Food Safety and Applied Nutrition, Food and Drug Admin. O Henao, PhD, E Scallan, PhD, F Angulo, DVM, P Griffin, MD, R Tauxe, MD, Div of Foodborne, Bacterial and Mycotic Diseases, National Center for Zoonotic, Vector-Borne and Enteric Diseases; E Barzilay, MD, EIS Officer, CDC.
In 2005, compared with the 1996--1998 baseline period, significant declines occurred in the estimated incidence of Campylobacter, Listeria, Salmonella, Shigella, STEC O157, and Yersinia infections. Several important food safety initiatives (1) might have contributed to the declines, indicating progress toward meeting the national health objectives (Table) (3). However, most progress occurred before 2005. Most of the decline in Campylobacter incidence occurred by 2001, with continued small decreases since then. The incidence of Listeria infections in 2005 is higher than its lowest point in 2002. Of the five most common Salmonella serotypes, only Typhimurium has declined, with most of the decline occurring by 2001. Most of the decline in STEC O157 incidence occurred during 2003 and 2004. The observed sustained increase in Vibrio incidence indicates that additional efforts are needed to prevent Vibrio infections. Oysters are the most important source of human Vibrio infections, and most human infections can be prevented by not eating raw or undercooked oysters. Measures that reduce Vibrio contamination of oysters also prevent illness.
Food animals are the most important source of human Salmonella infections. Transmission of Salmonella to humans can occur via various food vehicles, including eggs, meat, poultry, and produce, and via direct contact with animals and their environments. Testing by the U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) at slaughter and processing plants has demonstrated declines in Salmonella contamination of ground beef since 1998 (4). However FSIS recently announced a sustained increase in chicken-broiler carcasses testing positive for Salmonella during 2002--2005 and subsequently launched an initiative to reduce Salmonella in raw meat and poultry products (4,5). Although sources of infection with the most common Salmonella serotypes have been identified (e.g., food animals), further investigation is needed to identify sources for emerging Salmonella serotypes, such as Javiana and I 4,,12:i:-, a monophasic serotype that resembles S. Typhimurium except that it has no phase 2 flagellar antigen and has previously been misclassified as Group B Salmonella or S. Typhimurium (6).
Large outbreaks with multiple laboratory-confirmed cases can distort underlying trends in incidence. For example, the incidence of Cryptosporidium infections increased substantially from 2004 to 2005 because of a large outbreak associated with visits to a recreational water park in New York (P Smith, MD, New York State Department of Health, personal communication, 2006).
The findings in this report are subject to at least four limitations. First, FoodNet relies on laboratory diagnoses, but many foodborne illnesses are not diagnosed by clinical laboratories. Second, protocols for isolation of certain enteric pathogens (e.g., STEC non-O157) in clinical laboratories vary and are not uniform within and among FoodNet sites (7); others (e.g., norovirus) cannot readily be identified by clinical laboratories. Third, reported illnesses might have been acquired through nonfoodborne sources, and reported incidence rates do not reflect foodborne transmission exclusively. Finally, although the FoodNet surveillance population is similar to the U.S. population (2), the findings might not be generalizable to the entire U.S. population.
Much remains to be done to reach the national health objectives for foodborne illnesses. Enhanced measures are needed 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 measures can be particularly focused when the source of human infections (i.e., animal reservoir species and transmission route) are known. The declines in the incidence of STEC O157 infections observed in recent years suggest that coordinated efforts by regulators and industry have been effective in reducing contamination and illness related to ground beef (8,9).
Consumers can reduce their risk for foodborne illness by following safe food-handling recommendations and by avoiding consumption of unpasteurized milk and unpasteurized milk products, raw or undercooked oysters, raw or undercooked eggs, raw or undercooked ground beef, and undercooked poultry (additional information on food safety for consumers is available at http://www.fightbac.org). Other effective prevention measures, such as pasteurization of in-shell eggs, irradiation of ground meat, and pressure treatment of oysters, can also decrease the risk for foodborne illness.
* Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.
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Date last reviewed: 4/13/2006