Salmonella enterica PFGE Clusters | CDC EID

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Volume 16, Number 11–November 2010
Research
Salmonella enterica Pulsed-Field Gel Electrophoresis Clusters, Minnesota, USA, 2001–2007

Joshua M. Rounds, Comments to Author Craig W. Hedberg, Stephanie Meyer, David J. Boxrud, and Kirk E. Smith
Author affiliations: Minnesota Department of Health, St. Paul, Minnesota, USA (J.M. Rounds, S. Meyer, D.J. Boxrud, K.E. Smith); and University of Minnesota School of Public Health, Minneapolis, Minnesota, USA (C.W. Hedberg)

Suggested citation for this article

Abstract
We determined characteristics of Salmonella enterica pulsed-field gel electrophoresis clusters that predict their being solved (i.e., that result in identification of a confirmed outbreak). Clusters were investigated by the Minnesota Department of Health by using a dynamic iterative model. During 2001–2007, a total of 43 (12.5%) of 344 clusters were solved. Clusters of >4 isolates were more likely to be solved than clusters of 2 isolates. Clusters in which the first 3 case isolates were received at the Minnesota Department of Health within 7 days were more likely to be solved than were clusters in which the first 3 case isolates were received over a period >14 days. If resources do not permit investigation of all S. enterica pulsed-field gel electrophoresis clusters, investigation of clusters of >4 cases and clusters in which the first 3 case isolates were received at a public health laboratory within 7 days may improve outbreak investigations.

Salmonellosis is a major foodborne illness that results in ≈1.4 million infections, 15,000 hospitalizations, and 400 deaths each year in the United States (1,2). Salmonella infections are primarily of foodborne origin but can also occur through contact with infected animals, humans, or their feces (3). The epidemiology of salmonellosis is complex largely because there are >2,500 distinct serotypes (serovars) with different reservoirs and diverse geographic incidences (4). Changes in food consumption, production, and distribution have led to an increasing frequency of multistate outbreaks associated with fresh produce and processed foods (5).

The development of molecular subtyping by pulsed-field gel electrophoresis (PFGE) has revolutionized Salmonella spp. surveillance. The National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet) provides state and local public health department laboratories with standardized methods to subtype Salmonella serovars and normalize PFGE patterns against a global reference standard provided by the Centers for Disease Control and Prevention (CDC) (6,7). Molecular subtyping enhances case definition specificity, enabling outbreaks to be detected and controlled at an earlier stage, and enabling detection of geographically dispersed outbreaks (8–10).

Although the benefits of molecular subtyping, specifically by PFGE, in foodborne disease outbreak detection and investigation have been well established, there is no consensus about when a PFGE cluster warrants further investigation and almost no quantitative analysis about characteristics of PFGE clusters that indicate a common source will be identified (11–15). Cluster size and the number of days from receipt of the first cluster case isolate to the third case isolate received by the public health laboratory were predictors of a source of infection being identified for Listeria monocytogenes clusters in France (16). The objective of this study was to determine characteristics of Salmonella PFGE clusters that could serve as useful predictors for their being solved (i.e., result in identification of a confirmed outbreak). This information could help public health agencies with limited resources prioritize investigation of Salmonella PFGE clusters.

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Salmonella enterica PFGE Clusters | CDC EID

Suggested Citation for this Article

Rounds JM, Hedberg CW, Meyer S, Boxrud DJ, Smith KE. Salmonella enterica pulsed-field gel electrophoresis clusters, Minnesota, USA, 2001–2007. Emerg Infect Dis [serial on the Internet]. 2010 Nov [date cited]. http://www.cdc.gov/EID/content/16/11/1678.htm

DOI: 10.3201/eid1611.100368