Outbreak-associated Salmonella enterica Serotypes and Food Commodities, United States, 1998–2008

Brendan R. Jackson

, Patricia M. Griffin, Dana Cole, Kelly A. Walsh, and Shua J. Chai

Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

Salmonella enterica infections are transmitted not only by animal-derived foods but also by vegetables, fruits, and other plant products. To clarify links between Salmonella serotypes and specific foods, we examined the diversity and predominance of food commodities implicated in outbreaks of salmonellosis during 1998–2008. More than 80% of outbreaks caused by serotypes Enteritidis, Heidelberg, and Hadar were attributed to eggs or poultry, whereas > 50% of outbreaks caused by serotypes Javiana, Litchfield, Mbandaka, Muenchen, Poona, and Senftenberg were attributed to plant commodities. Serotypes Typhimurium and Newport were associated with a wide variety of food commodities. Knowledge about these associations can help guide outbreak investigations and control measures.

Salmonella enterica is estimated to cause 1.2 million illnesses each year in the United States and to be the leading cause of hospitalizations and deaths from foodborne disease (1). Because of the major public health role of Salmonella infections, the US Department of Health and Human Services has made decreasing the nationwide incidence of these infections by 25% a Healthy People 2020 national goal (2). Overall, salmonellosis incidence has not decreased in the past decade; the incidence has substantially increased for some serotypes and decreased for others (2,3). Focused attention on determining sources of Salmonella infections will be vital to reach the 25% target reduction in these infections.
Salmonella serotypes differ in their natural reservoirs and ability to cause human infections (4– 6); only a small proportion of > 2,500 serotypes cause most human infections (4,7). In 2009, only 20 serotypes comprised > 82% of the ≈36,000 serotyped human-derived Salmonella isolates in the United States that were reported to the Centers for Disease Control and Prevention (3). A few serotypes have been associated with specific animal reservoirs. For example, serotype Dublin, which caused 103 laboratory-confirmed human infections in 2009 (3), is found predominantly in cattle (5). However, reservoir sampling alone has limited use in predicting the contribution of a reservoir to the incidence of human illness (8).
Outbreak data and case–control studies have linked some serotypes to certain foods or exposures (e.g., serotype Enteritidis to eggs and chicken) (9–11). Information obtained during outbreak investigations is a key tool in understanding which foods are common sources of pathogens contributing to foodborne infections. During outbreak investigations, illnesses can be linked to a particular food by using epidemiologic or laboratory evidence (12). To our knowledge, no systematic examination of Salmonella serotypes and food vehicles implicated in outbreaks has been reported. We analyzed foodborne disease outbreak data to determine associations between food commodities and serotypes to help inform future outbreak investigations, foodborne illness source attribution analyses, and control measures.