Incidence and Trends of Infection with Pathogens Transmitted Commonly Through Food — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 1996–2012

Foodborne diseases are an important public health problem in the United States. The Foodborne Diseases Active Surveillance Network* (FoodNet) conducts surveillance in 10 U.S. sites for all laboratory-confirmed infections caused by selected pathogens transmitted commonly through food to quantify them and monitor their incidence. This report summarizes 2012 preliminary surveillance data and describes trends since 1996. A total of 19,531 infections, 4,563 hospitalizations, and 68 deaths associated with foodborne diseases were reported in 2012. For most infections, incidence was highest among children aged <5 years; the percentage of persons hospitalized and the percentage who died were highest among persons aged ≥65 years. In 2012, compared with the 2006–2008 period, the overall incidence of infection† was unchanged, and the estimated incidence of infections caused by Campylobacter and Vibrio increased. These findings highlight the need for targeted action to address food safety gaps.

FoodNet conducts active, population-based surveillance for laboratory-confirmed infections caused by Campylobacter, Cryptosporidium, Cyclospora, Listeria, Salmonella, Shiga toxin–producing Escherichia coli (STEC) O157 and non-O157, Shigella, Vibrio, and Yersinia in 10 sites covering 15% of the U.S. population (48 million persons in 2011).§ FoodNet is a collaboration among CDC, 10 state health departments, the U.S. Department of Agriculture's Food Safety and Inspection Service (USDA-FSIS), and the Food and Drug Administration (FDA). Hospitalizations occurring within 7 days of specimen collection date are recorded, as is the patient's vital status at hospital discharge, or at 7 days after the specimen collection date if the patient was not hospitalized. All hospitalizations and deaths that occurred within a 7-day window are attributed to the infection. Surveillance for physician-diagnosed postdiarrheal hemolytic uremic syndrome (HUS), a complication of STEC infection characterized by renal failure, is conducted through a network of nephrologists and infection preventionists and by hospital discharge data review. This report includes 2011 HUS data for persons aged <18 years.

Incidence was calculated by dividing the number of laboratory-confirmed infections in 2012 by U.S. Census estimates of the surveillance population area for 2011.¶ A negative binomial model with 95% confidence intervals (CIs) was used to estimate changes in incidence from 2006–2008 to 2012 and from 1996–1998 to 2012 (1). The overall incidence of infection with six key pathogens for which >50% of illnesses are estimated to be foodborne (Campylobacter, Listeria, Salmonella, STEC O157, Vibrio, and Yersinia) was calculated (2). Trends were not assessed for Cyclospora because data were sparse, or for STEC non-O157 because of changes in diagnostic practices. For HUS, changes in incidence from 2006–2008 to 2011 were estimated.

Incidence and Trends

In 2012, FoodNet identified 19,531 laboratory-confirmed cases of infection (Table 1). The number of infections and incidence per 100,000 population, by pathogen, were as follows: Salmonella (7,800; 16.42), Campylobacter (6,793; 14.30), Shigella (2,138; 4.50), Cryptosporidium (1,234; 2.60), STEC non-O157 (551; 1.16), STEC O157 (531; 1.12), Vibrio (193; 0.41), Yersinia (155; 0.33), Listeria (121; 0.25), and Cyclospora (15; 0.03). As usual, the highest reported incidence was among children aged <5 years for Cryptosporidium and the bacterial pathogens other than Listeria and Vibrio, for which the highest incidence was among persons aged ≥65 years (Table 2).

Among 6,984 (90%) serotyped Salmonella isolates, the top three serotypes were Enteritidis, 1,238 (18%); Typhimurium, 914 (13%); and Newport, 901 (13%). Among 183 (95%) Vibrio isolates with species information, 112 were V. parahaemolyticus (61%), 25 were V. vulnificus (14%), and 20 were V. alginolyticus (11%). Among 496 (90%) serogrouped STEC non-O157 isolates, the most common serogroups were O26 (27%), O103 (23%), and O111 (15%). Among 2,318 (34%) Campylobacter isolates with species information, 2,082 (90%) were C. jejuni, and 180 (8%) were C. coli.

The estimated incidence of infection was higher in 2012 compared with 2006–2008 for Campylobacter (14% increase; confidence interval [CI]: 7%–21%) and Vibrio (43% increase; CI: 16%–76%) and unchanged for other pathogens (Figure 1). In comparison with 1996–1998, incidence of infection was significantly lower for Campylobacter, Listeria, Shigella, STEC O157, and Yersinia, whereas the incidence of Vibrio infection was higher (Figure 2). The overall incidence of infection with six key pathogens** transmitted commonly through food was lower in 2012 (22% decrease; CI: 11%–32%) compared with 1996–1998 and unchanged compared with 2006–2008.

The incidence of infections with specific Salmonella serotypes in 2012, compared with 2006–2008, was lower for Typhimurium (19% decrease; CI: 10%–28%), higher for Newport (23% increase; CI: 1%–50%), and unchanged for Enteritidis. Compared with 1996–1998, the incidence of infection was significantly higher for Enteritidis and Newport, and lower for Typhimurium.

Among 63 cases of postdiarrheal HUS in children aged <18 years (0.57 cases per 100,000 children) in 2011, 33 (52%) occurred in children aged <5 years (1.09 cases per 100,000). Compared with 2006–2008, the incidence was significantly lower for children aged <5 years (44% decrease; CI: 18%–62%) and for children aged <18 years (29% decrease; CI: 4%–47%).

Hospitalizations and Deaths

In 2012, FoodNet identified 4,563 hospitalizations and 68 deaths among cases of infection with pathogens transmitted commonly through food (Table 1). The percentage of patients hospitalized ranged from 15% for Campylobacter to 96% for Listeria infections. The percentage hospitalized was greatest among those aged ≥65 years for STEC O157 (67%), Vibrio (58%), Salmonella (55%), Cyclospora (50%), Shigella (41%), STEC non-O157 (34%), Cryptosporidium (33%), and Campylobacter (31%). At least 95% of patients with Listeria infection in each age group†† with cases were hospitalized. The percentage of patients who died ranged from 0% for Yersinia and Cyclospora to 11% for Listeria infections. The percentage that died was highest among persons aged ≥65 years for Vibrio (6%), Salmonella (2%), STEC O157 (2%), Cryptosporidium (1%), Shigella (1%), and Campylobacter (0.2%).

Reported by

Debra Gilliss, MD, California Dept of Public Health. Alicia B. Cronquist, MPH, Colorado Dept of Public Health and Environment. Matthew Cartter, MD, Connecticut Dept of Public Health. Melissa Tobin-D'Angelo, MD, Georgia Dept of Public Health. David Blythe, MD, Maryland Dept of Health and Mental Hygiene. Kirk Smith, DVM, Minnesota Dept of Health. Sarah Lathrop, PhD, Univ of New Mexico. Shelley Zansky, PhD, New York State Dept of Health. Paul R. Cieslak, MD, Oregon Health Authority. John Dunn, DVM, Tennessee Dept of Health. Kristin G. Holt, DVM, Food Safety and Inspection Svc, US Dept of Agriculture. Susan Lance, Center for Food Safety and Applied Nutrition, Food and Drug Admin. Stacy M. Crim, MPH, Olga L. Henao, PhD, Mary Patrick, MPH, Patricia M. Griffin, MD, Robert V. Tauxe, MD, Div of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC. Corresponding contributor: Stacy M. Crim, scrim@cdc.gov, 404-639-2257.

Editorial Note

In 2012, the incidence of infections caused by Campylobacter and Vibrio increased from the 2006–2008 period, whereas the incidence of infections caused by Cryptosporidium, Listeria, Salmonella, Shigella, STEC O157, and Yersinia was unchanged. These findings highlight the need to continue to identify and address food safety gaps that can be targeted for action by the food industry and regulatory authorities.

After substantial declines in the early years of FoodNet surveillance, the incidence of Campylobacter infection has increased to its highest level since 2000. Campylobacter infections are more common in the western U.S. states and among children aged <5 years (3). Although most infections are self-limited, sequelae include reactive arthritis and Guillain-Barré syndrome.§§ Associated exposures include consumption of poultry, raw milk, produce, and untreated water, and animal contact (4,5).

Declines in U.S. campylobacteriosis during 1996–2001 might have been related to measures meat and poultry processors implemented to comply with the Pathogen Reduction and Hazard Analysis and Critical Control Points (HACCP) systems regulations issued by USDA-FSIS in the late 1990s.¶¶ In 2011, USDA-FSIS issued new Campylobacter performance standards for U.S. chicken and turkey processors.*** Continued FoodNet surveillance can help to assess the public health impact of these standards and other changes. Detailed patient exposure information coupled with information on strain subtypes could help in assessing the relative contribution of various sources of infection and the effectiveness of control measures.

Although a significant increase was observed in reported Vibrio infections, the number of such infections remains low (6). Vibrios live naturally in marine and estuarine waters, and many infections are acquired by eating raw oysters (7). These infections are most common during warmer months, when waters contain more Vibrio organisms. Infections can be prevented by postharvest treatment of oysters with heat, freezing, or high pressure (8), or by thorough cooking. Persons who are immunocompromised or have impaired liver function should be informed that consuming raw seafood carries a risk for severe Vibrio infection. Vibrios also cause wound and soft-tissue infections among persons who have contact with water; for example, Vibrio alginolyticus typically causes ear infection (9).

The decrease in incidence of HUS in 2011 compared with 2006–2008 mirrors the decrease in the incidence of STEC O157 infection observed in 2011. The incidence of STEC O157 infection, which had declined since 2006, was no longer decreasing in 2012, and now exceeds the previously met Healthy People 2010 target of one case per 100,000 persons. The continued increase in STEC non-O157 infections likely reflects increasing use by clinical laboratories of tests that detect these infections.

FoodNet surveillance relies on isolation of bacterial pathogens by culture of clinical specimens; therefore, the increasing use of culture-independent tests for Campylobacter and STEC might affect the reported incidence of infection (10). Data on persons with only culture-independent evidence of infection suggests that in 2012, the number of laboratory-identified Campylobacter cases could have been 9% greater and the number of STEC (O157 and non-O157) cases 7%–19% greater than that reported (CDC, unpublished data, 2013). The lack of recent decline in STEC O157 incidence is of concern; continued monitoring of trends in the incidence of HUS and use of culture-independent testing might aid in interpreting future data on STEC O157 incidence.

The findings in this report are subject to at least four limitations. First, health-care–seeking behaviors and other characteristics of the population in the surveillance area might affect the generalizability of the findings. Second, many infections transmitted commonly through food (e.g., norovirus infection) are not monitored by FoodNet because these pathogens are not identified routinely in clinical laboratories. Third, the proportion of illnesses transmitted by nonfood routes differs by pathogen, and the route cannot be determined for individual, nonoutbreak-associated illnesses and, therefore, the data provided in this report do not exclusively relate to infections from foodborne sources. Finally, in some cases counted as fatal, the infection with the enteric pathogen might not have been the primary cause of death.

Most foodborne illnesses can be prevented. Progress has been made in decreasing contamination of some foods and reducing illness caused by some pathogens, as evidenced by decreases in earlier years. In 2010, FDA passed the Egg Safety Rule,††† designed to decrease contamination of shell eggs with Salmonella serotype Enteritidis. In 2011, USDA-FSIS tightened its performance standard for Salmonella contamination to a 7.5% positive rate for whole broiler chickens.§§§ Finally, the Food Safety Modernization Act of 2011 gives FDA additional authority to improve food safety and requires CDC to strengthen surveillance and outbreak response.¶¶¶ Collection of comprehensive surveillance information further supports reductions in foodborne infections by helping to determine where to target prevention efforts, supporting efforts to attribute infections to sources, guiding implementation of measures known to reduce food contamination, and informing development of new measures. Because consumers can bring an added measure of safety during food storage, handling, and preparation, they are advised to seek out food safety information, which is available online.****

Acknowledgments

Workgroup members, Foodborne Diseases Active Surveillance Network (FoodNet), Emerging Infections Program; communications team, Div of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Diseases, CDC.

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