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CDC Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food

The Foodborne Diseases Active Surveillance Network (FoodNet) of CDC’s Emerging Infections Program conducts active, population-based surveillance in 10 U.S. states for all laboratory-confirmed infections with select enteric pathogens transmitted commonly through food. This report describes preliminary surveillance data for 2009 and trends in incidence since 1996. In 2009, a total of 17,468 laboratory-confirmed cases of infection were identified. In comparison with the first 3 years of surveillance (1996–1998), sustained declines in the reported incidence of infections caused by Campylobacter, Listeria, Salmonella, Shiga toxin-producing Escherichia coli (STEC) O157, Shigella, and Yersinia were observed. The incidence of Vibrio infection continued to increase. Compared with the preceding 3 years (2006–2008), significant decreases in the reported incidence of Shigella and STEC O157 infections were observed. For most infections, reported incidence was highest among children aged <4 years; the percentage of persons hospitalized and the case fatality rate (CFR) were highest among persons aged ≥50 years. In 2009, the Healthy People 2010 target of ≤1.0 case per 100,000 population for STEC O157 infection (objective 10-1b) was met. Further collaborative efforts with regulatory agencies and industry are needed to sustain and extend recent declines and to improve prevention of foodborne infections.

Surveillance Methods – FoodNet* is a collaborative program among CDC, 10 state health departments,† the U.S. Department of Agriculture’s Food Safety and Inspection Service, and the Food and Drug Administration (FDA). It 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. FoodNet personnel regularly contact clinical laboratories to ascertain laboratory-confirmed cases of infection occurring within the surveillance sites. Hospitalizations occurring within 7 days of specimen collection date are recorded, as is the patient’s status at hospital discharge or at 7 days after the specimen collection date if not hospitalized. Deaths and hospitalizations are attributed to the pathogen if they occur within 7 days of the specimen collection date, regardless of actual cause.

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. Hospital discharge data are reviewed to validate HUS diagnoses and verify the presence of diarrhea in the 21 days before HUS onset. This report contains preliminary postdiarrheal HUS data for 2008, rather than for 2009, because additional time is needed to review hospital records.

Incidence rates for 2009 were calculated by dividing the number of laboratory-confirmed infections by U.S. Census Bureau population estimates for 2008. Final incidence rates will be reported when population estimates for 2009 are available. Case fatality rates (CFRs) were calculated by dividing the number of deaths by the number of laboratory-confirmed infections and multiplying by 100.

Surveillance Results – In 2009, a total of 17,468 laboratory-confirmed cases of infection were identified. The number of reported infections and incidence per 100,000 population, by pathogen, were as follows: Salmonella (7,039; 15.19), Campylobacter (6,033; 13.02), Shigella (1,849; 3.99), Cryptosporidium (1,325; 2.86), STEC O157 (459; 0.99), STEC non-O157 (264; 0.57), Vibrio (160; 0.35), Listeria (158; 0.34), Yersinia (150; 0.32), and Cyclospora (31; 0.07). Incidence varied among FoodNet sites. Incidence was highest in children aged <4 years for Salmonella (72.93), Campylobacter (28.70), Shigella (16.61), Cryptosporidium (5.36), STEC O157 (3.84), STEC non-O157 (2.72), and Yersinia (2.36) infections, and in persons aged ≥50 years for Listeria (0.82), Vibrio (0.62), and Cyclospora (0.11) infections.

The percentage of patients hospitalized ranged from 12.9% for Cyclospora infections to 89.2% for Listeria infections. The percentage hospitalized was highest among those aged ≥50 years for STEC O157 (59.4%), Salmonella (45.2%), Yersinia (43.2%), Vibrio (40.7%), STEC non-O157 (34.2%), Shigella (29.4%), Cyclospora (26.7%), Cryptosporidium (24.7%), and Campylobacter (21.3%) infections, and in children aged <4 years for Listeria (94.1%) infections. CFRs ranged from 0.05% for Shigella infections to 12.7% for Listeria infections. The CFR was highest in persons aged ≥50 years for Listeria (17.5%), Vibrio (8.1%), Yersinia (5.4%), STEC non-O157 (2.6%), STEC O157 (1.5%), Salmonella (1.2%), Cryptosporidium (1.1%), and Campylobacter (0.5%) infections. No deaths were reported for Cyclospora infections.

Among 6,371 (90.5%) Salmonella isolates serotyped, 10 serotypes accounted for 73.1% of infections: Enteritidis, 1,226 (19.2%); Typhimurium, 1,024 (16.1%); Newport, 772 (12.1%); Javiana, 544 (8.5%); Heidelberg, 230 (3.6%); Montevideo, 206 (3.2%); I 4,[5],12:i:-, 197 (3.1%); Muenchen, 170 (2.7%); Saintpaul, 157 (2.5%); and Oranienburg, 132 (2.1%).§ Among 154 (96.3%) Vibrio isolates with species information, 80 (52.0%) were parahaemolyticus, 22 (14.3%) were vulnificus, and 22 (14.3%) were alginolyticus . Among 264 STEC non-O157 isolates tested for O antigen, 235 (89.0%) had O antigen identified; the most common were O26 (28.9%), O103 (20.0%), and O111 (14.9%).

In 2008, FoodNet identified 64 cases of postdiarrheal HUS in persons aged <18 years (0.60 cases per 100,000). Among those, 42 (65.6%) occurred in children aged <5 years (1.40 cases per 100,000).

Comparison with Previous Years – A main effects, log-linear Poisson regression model (negative binomial) was used to estimate changes in incidence of infections in 2009 compared with previous years. This model accounts for site-to-site variation and changes in the size of the population under surveillance in FoodNet over time (1). The average annual incidence during 1) the first 3 years of surveillance (1996–1998) and 2) the preceding 3 years (2006–2008) were used for comparison. The estimated change in incidence between 2009 and the comparison periods was calculated with 95% confidence intervals (CI). For HUS surveillance, the average annual incidence for 2005–2007 was used as the comparison period. Changes over time were not evaluated for STEC non-O157 and Cyclospora.

In comparison with 1996–1998, rates of infection in 2009 were lower for Shigella (55% decrease, CI = 37%–68%), Yersinia (53% decrease, CI = 41%–63%), STEC O157 (41% decrease, CI = 27%–52%), Campylobacter (30% decrease, CI = 24%–35%), Listeria (26% decrease, CI = 8%–40%), and Salmonella (10% decrease CI = 3%–16%); rates were higher for Vibrio (85% increase, CI = 36%–150%). The incidence of infection with Cryptosporidium did not change significantly. The incidence of Vibrio infection has been increasing since approximately 2001 and the most marked decreases in Campylobacter, Listeria, and Salmonella infections occurred before 2004. The incidence of STEC O157 infection in 2009 was similar to that in 2004. In comparison with 2006–2008, the rates of Shigella (27% decrease, CI = 4%–44%) and STEC O157 (25% decrease, CI = 10%–37%) infection were significantly lower.

The incidence of infections with specific Salmonella serotypes in 2009, compared with 1996–1998, was lower for Typhimurium (51% decrease, CI = 44%–56%), Agona (48% decrease, CI = 26%–63%), Heidelberg (33% decrease, CI = 13%–48%), and Thompson (33% decrease, CI = 2%–55%), and higher for Javiana (120% increase, CI = 44%–235%), Newport (64% increase, CI = 27%–113%), Oranienburg (39% increase, CI = 2%–90%), and Enteritidis (32% increase, CI = 8%–61%). Compared with 2006–2008, only Oranienburg (35% increase, CI = 6%–73%) and I 4,[5],12,i:- (42% decrease, CI = 18%–59%) were significantly different. The incidence of postdiarrheal HUS in children aged <5 years and in persons aged <18 years did not change significantly in 2008 compared with 2005–2007.