Characteristics of Clusters of Salmonella and Escherichia coli O157 Detected by Pulsed-Field Gel Electrophoresis that Predict Identification of Outbreaks.
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.



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.



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.



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 Tennessee Department of Health , Nashville, Tennessee.
Timothy F
TF
Jones
1 Tennessee Department of Health , Nashville, Tennessee.
Nupur
N
Sashti
1 Tennessee Department of Health , Nashville, Tennessee.
Amanda
A
Ingram
2 Connecticut Department of Public Health , Hartford, Connecticut.
Quyen
Q
Phan
3 Oregon Public Health Division , Portland, Oregon.
Hillary
H
Booth
4 Minnesota Department of Health , St. Paul, Minnesota.
Joshua
J
Rounds
5 New Mexico Emerging Infections Program , Albuquerque, New Mexico .
Cyndy S
CS
Nicholson
6 Colorado Department of Public Health and Environment , Denver, Colorado.
Shaun
S
Cosgrove
7 Maryland Department of Health and Mental Hygiene , Baltimore, Maryland.
Kia
K
Crocker
8 Centers for Disease Control and Prevention , Atlanta, Georgia .
L Hannah
LH
Gould
D002487:Centers for Disease Control and Prevention, U.S.; D018563:Disease Notification; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000145:classification / Q000302:isolation & purification*; D059022:Food Safety; D005517:Foodborne Diseases / Q000453:epidemiology / Q000382:microbiology*; D005759:Gastroenteritis / Q000453:epidemiology / Q000382:microbiology; D006801:Humans; D008954:Models, Biological; D058889:Molecular Typing; D011446:Prospective Studies; D015980:Public Health Practice; D012475:Salmonella / Q000145:classification / Q000302:isolation & purification*; D012478:Salmonella Food Poisoning / Q000453:epidemiology / Q000382:microbiology*; D062211:Spatio-Temporal Analysis; D014481:United States / Q000453:epidemiology; D016885:United States Department of Agriculture; D014486:United States Food and Drug Administration
foodborne disease; outbreaks; pulsed field gel electrophoresis (PFGE)