INTRODUCTION
Molecular subtyping of pathogens is critical for foodborne disease outbreak detection and investigation. Many clusters initially identified by pulsed-field gel electrophoresis (PFGE) are not confirmed as point-source outbreaks. We evaluated characteristics of clusters that can help prioritize investigations to maximize effective use of limited resources.
MATERIALS AND METHODS
A multiagency collaboration (FoodNet) collected data on Salmonella and Escherichia coli O157 clusters for 3 years. Cluster size, timing, extent, and nature of epidemiologic investigations were analyzed to determine associations with whether the cluster was identified as a confirmed outbreak.
RESULTS
During the 3-year study period, 948 PFGE clusters were identified; 849 (90%) were Salmonella and 99 (10%) were E. coli O157. Of those, 192 (20%) were ultimately identified as outbreaks (154 [18%] of Salmonella and 38 [38%] of E. coli O157 clusters). Successful investigation was significantly associated with larger cluster size, more rapid submission of isolates (e.g., for Salmonella, 6 days for outbreaks vs. 8 days for nonoutbreaks) and PFGE result reporting to investigators (16 days vs. 29 days, respectively), and performance of analytic studies (completed in 33% of Salmonella outbreaks vs. 1% of nonoutbreaks) and environmental investigations (40% and 1%, respectively). Intervals between first and second cases in a cluster did not differ significantly between outbreaks and nonoutbreaks.
CONCLUSIONS
Molecular subtyping of pathogens is a rapidly advancing technology, and successfully identifying outbreaks will vary by pathogen and methods used. Understanding criteria for successfully investigating outbreaks is critical for efficiently using limited resources.
[1]
K. Everstine,et al.
Characteristics of foodborne disease outbreak investigations conducted by Foodborne Diseases Active Surveillance Network (FoodNet) sites, 2003-2008.
,
2012,
Clinical infectious diseases : an official publication of the Infectious Diseases Society of America.
[2]
P. Gerner-Smidt,et al.
Nonculture Diagnostic Tests for Enteric Diseases
,
2012,
Emerging infectious diseases.
[3]
D. Boxrud,et al.
Dynamics of Escherichia coli O157:H7 outbreak detection and investigation, Minnesota 2000–2008
,
2011,
Epidemiology and Infection.
[4]
D. Boxrud,et al.
Salmonella enterica Pulsed-Field Gel Electrophoresis Clusters, Minnesota, USA, 2001–2007
,
2010,
Emerging infectious diseases.
[5]
J. Besser,et al.
The Role, Challenges, and Support of PulseNet Laboratories in Detecting Foodborne Disease Outbreaks
,
2010,
Public health reports.
[6]
Donald J. Sharp,et al.
Timeliness of Enteric Disease Surveillance in 6 US States
,
2008,
Emerging infectious diseases.