Foodborne Infections—Preliminary 2005 FoodNet Data

Abstract and Commentary

By Mary-Louise Scully, MD

Sansum-Santa Barbara Medical Foundation Clinic, Santa Barbara, CA

Dr. Scully reports no financial relationship relevant to this field of study.

Synopsis: Preliminary FoodNet surveillance data for 2005 show the incidence of infections caused by Campylobacter, Listeria, Salmonella, Shiga toxin-producing Escherichia coli 0157, Shigella, and Yersinia have declined, whereas Vibrio infections have increased.

Source: CDC. Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food—10 States, United States, 2005. MMWR Morb Mortal Wkly Rep. 2006;55:392-395.

In 1996, the Foodborne Diseases Active Surveillance Network (FoodNet) was established as a collaborative effort by the Emerging Infections Program of the CDC, the US Department of Agriculture (USDA), the Food Safety and Inspection Service (FSIS), and the US Food and Drug Administration (FDA). FoodNet now includes 10 state health departments (California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, and Tennessee) which monitor laboratory-confirmed infections of 7 bacterial organisms (Campylobacter, Listeria, Salmonella, Shiga toxin-producing Escherichia coli 0157 (STEC 0157), Shigella, Vibrio, and Yersinia) and 2 parasitic (Cryptosporidium and Cyclospora) infections. Since 2000, FoodNet is also collecting data on Shiga toxin-producing Escherichia coli non-0157 (STEC non-0157) and hemolytic uremic syndrome (HUS). The surveillance population of FoodNet is now 44.5 million (15% of the US population), and new data for 2005 can be compared with baseline FoodNet data from the period 1996-1998 to examine trends in the incidence of foodborne infections.

A total of 16,614 laboratory-confirmed foodborne illness cases were identified in FoodNet surveillance areas. Salmonella cases were most frequent (6471 cases), with the most common serotypes being Typhimurium (19%), Enteritidis (18%), Newport (10%), Heidelberg (6%), and Javiana (5%). Cases of Campylobacter (5655), Shigella (2078), and Cryptosporidium (1313) followed in frequency. STEC 0157 accounted for 473 cases, an estimated decrease of 29% compared to FoodNet data from 1996-1998. Most of the decline in STEC 0157 incidence occurred during 2003 and 2004. Yersinia (159 cases), STEC non-0157 (146 cases), Listeria (135 cases), Vibrio (119 cases), and Cyclospora (65 cases) made up the remainder of cases.

Compared with the 1996-1998 FoodNet baseline period, the estimated incidence of Campylobacter, Listeria, Salmonella, Shigella, STEC 0157, and Yersinia all declined significantly. Food safety initiatives may have contributed to these declines. The estimated incidence of Vibrio infections increased by 41% compared to baseline, indicating additional efforts are needed to prevent Vibrio infections. Consumption of raw or undercooked oysters is a risk factor for acquisition of Vibrio infections.

Commentary

It is estimated that foodborne diseases secondary to known pathogens cause 14 million illnesses, 60,000 hospitalizations, and 1800 deaths in the United States each year.1 Foodborne illness often begins with an acute onset of nausea, vomiting, diarrhea, or other gastrointestinal problems. The illness can be self-limited but severe illness, bacteremia, and death are more likely to occur in the very young, elderly, or patients with compromised immune systems. In the United States, older patients represent an increasing proportion of the population. Associated chronic diseases, lower nutritional status, loss of mobility, overuse of H-2 receptor antagonists (hypochlohydria may reduce the ability to resist infection), and improper food preparation and handling can all contribute to the increased risk and severity of foodborne infections in older adults.2 The risk for foodborne illness can be reduced by avoiding consumption of unpasteurized milk or milk products and raw or undercooked food products, especially eggs, oysters, poultry, or ground beef.

The FoodNet data represent only culture-confirmed laboratory cases of foodborne illness. Many patients may not seek medical attention during foodborne illness and, even if seen by a physician, appropriate stool studies are not always ordered. The Infectious Disease Society of America (IDSA) practice guidelines for infectious diarrhea address this issue by recommending that any patient with community-acquired diarrhea lasting greater than 1 day, especially if accompanied by fever, dehydration, bloody stools, systemic illness, recent antibiotic use, day care center attendance, or hospitalization should have appropriate stool studies.3 The presence of bloody diarrhea should prompt evaluation for Shiga toxin production if the laboratory has that capability. Ideally, isolates that are positive for Shiga toxin should then be sent to a state public health laboratory for confirmation and STEC serotying. Most laboratories do not have the ability to identify noroviruses, an increasingly recognized cause of foodborne illness. In the future, 2 of the FoodNet laboratories will be implementing a new diagnostic panel for acute diarrheal episodes of unknown etiology, and this information may lead to the identification of new foodborne pathogens.4

After E. coli 0157 outbreaks associated with ground beef occurred in 1996, the Pathogen Reduction/Hazard Analysis Critical Control Points (HACCP) system of regulation was established. This resulted in the implementation of sampling and microbiologic testing for Salmonella in meat instead of only visual inspection of carcasses. These measures likely contributed to the documented decline in bacterial pathogens since 1996-1998 noted in the FoodNet data. Of note, the rise in FoodNet Vibrio infections was not related to Hurricane Katrina since the Vibrio cases seen in the aftermath of the hurricane were mostly wound infections (24 cases), with only 4 reported cases of Vibrio gastrointestinal disease.5

Two outbreaks of multi-drug resistant (MDR) Salmonella in ground beef occurred in 2003-2004, heightening the concern about the need for surveillance of MDR outbreaks, as well as the development of control strategies. These strategies include improving mechanisms for trace-back investigations, designation of MDR Salmonella as an adulterant in ground beef, and restricting the use of antimicrobial agents in food animals.5 Restriction of antimicrobial use in food animals is receiving increasing support from consumer groups and public health officials. The WHO has advocated emphasis on restricting the use of critically important antibiotics for human medicine, such as fluoroquinolones, carbapenems, and third generation cephalosporins.6 A favorable trend toward decreasing the amount of drug-resistant bacteria (ie, vancomycin-resistant enterococci) was noted after the European Union put into place a ban on the use of 4 antibiotics for growth promotion in their food animals.7 Implementation of similar measures in the United States and other countries would likely make a significant contribution toward reducing future problems with foodborne resistant bacteria.

References

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  7. World Health Organization (WHO). Critically Important Antibacterial Agents for Human Medicine for Risk Management Strategies of Non-human Use: Report of a WHO Working Group Consultation, Canberra, Australia, 15-18 February 2005. www.who.int/foodborne_disease/resistance/en Accessed 11 May 2006.
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