Role of PulseNet in Listeriosis Surveillance and Outbreak Investigations Lewis M. Graves and Bala Swaminathan Foodborne and Diarrheal Diseases Branch National Center for Infectious Diseases Centers for Disease Control and Prevention
Outline � Laboratory-based Surveillance for Listeriosis � What is PulseNet—The Role of PulseNet � Listeria monocytogenes (Lm) on PulseNet (Goals) � Examples of PulseNet at work in Epidemiologic Investigations � Multistate Outbreak of Listeriosis—United States, 1998 � Tracking of Epidemic Clones � PulseNet at Work – Deli turkey meat outbreak, 2000 � Listeriosis Outbreak, Northeastern United States – 2002 � PulseNet: Future Improvements � Conclusions
Lab Based Surveillance for Listeriosis Serotyping � � Classical typing method based on somatic (O) and flagellar (H) antigens � Excellent first level typing method � >95% of human Lm infections belong to serotypes 1/2a, 1/2b, and 4b Ribotyping � Satisfies two requirements for a good subtyping method: typeability and reproducibility � Discriminating ability, particularly for serotype 4b, may not be adequate for epidemiological investigations � Automated robotic system commercially available (RiboPrinter, Qualicon) � Adequate for screening food processing plant environments Pusled-field gel electrophoresis (PFGE) � � Molecular subtyping method based on DNA macrorestriction analysis � Satisfies the requirements for a good subtyping method: typeability, reproducibility, and high discriminating ability � Excellent tool for epidemiological investigations
What is PulseNet? � A national network of public health laboratories � State health departments, Local health departments, Federal agencies (CDC, USDA/FSIS, FDA) � Perform standardized molecular typing of foodborne disease-causing bacteria by Pulsed- field gel electrophoresis (PFGE) � Share DNA “fingerprints” electronically via Internet � Dynamic database of DNA “fingerprints” at CDC � Database available on-demand to participants
Role of PulseNet � Detect foodborne disease case clusters by PFGE � Facilitate early identification of common source outbreaks � Assist epidemiologists in investigating outbreaks � Separate outbreak-associated cases from other sporadic cases � Assist in rapidly identifying the source of outbreaks � Act as a rapid and effective means of communication between public health laboratories
Listeria monocytogenes on PulseNet (Goals) � Early recognition � Investigation � Identify appropriate controls for case-control studies � Confirm Food etiology � Confirm environmental association � Identification of potential virulent and avirulent strains � Tracking of epidemic clones
Multistate Outbreak of Listeriosis—United States, 1998 During the 1998 hot dog (Franks) associated outbreak, all L. � monocytogenes PFGE subtyping was done by CDC and only 1 or 2 public health laboratories � 101 outbreak-related cases Epidemiologic investigation implicated hot dogs � Outbreak strains (serotype 4b) were isolated from patient’s opened � packages of Franks and unopened packages obtained from Plant B � MPN below the minimum quantifiable limit of 3-tube MPN Recall of over 35 million lbs. from Plant B � Additionally, 3 deli meat products produced at Plant B tested � positive for L. monocytogenes serotype 1/2a � No patient isolate match found � Product had been distributed and consumed, but no illness to this product were identified
Tracking of Epidemic Clones Epidemic Clone I (ECI) � � Small number of closely related strains of Lm serotype 4b � Implicated in numerous outbreaks of foodborne listeriosis during the past 2 decades in Europe and North America including those in Nova Scotia (coleslaw, 1981), California (Mexican-style cheese, 1985), Switzerland (soft cheese, ), France (pork tongue in aspic, 1992), and others) Epidemic Clone II (ECII) � � Lm serotype 4b, may represent a novel epidemic-associated lineage � Identified in the 1998 hot dog outbreak � Differed significantly in a portion of the genome that was otherwise highly conserved among strains of ECI, serotype 4b Evans et al . (2004) Manuscript in press, AEM
PulseNet at Work 2000 � Sept. 27, 2000: A posting by NY City Public Health Laboratory on PulseNet Listserv: 8 L. monocytogenes isolates of the same Ribotype and PFGE type in previous 3 months � Search of the National database and replies by participants identified matching isolates from 7 other states � Epi investigation led to implication of deli turkey meat product produced by a single food processing facility � Resulted in a recall of 16.8 million pound of product � No additional matches seen after recall
Apa I and Asc I Digest Pattern of Clinical Isolates Associated With the 2000 Turkey Deli Meat Linked Outbreak 44 45 77 76 127 126 178 179 187 187 200 200 206 206 225 227 245 246 255 257 266 268 271 272 289 290 298 298 307 308 292 293 308 308 340 322 341 323 329 328 350 350 354 336 355 337 345 346 351 371 372 352 381 381 Apa I Asc I
Listeriosis Outbreak, Northeastern United States - 2002 PFGE subtyping by CDC and 6 states helped epidemiologists � separate outbreak related cases from sporadic cases � 135 cases between 7/2 – 10/4 � 46 were the same PFGE pattern Epidemiologic investigation implicated turkey deli meat � USDA/FSIS promptly analyzed food and environmental � samples and subtyped Listeria monocytogenes isolates Outbreak strain found in environmental isolates from Plant A � and in intact product from Plant B Recall of over 30 million lbs. from Plants A and B � No additional matches identified after recall of product �
2002 Outbreak in U.S., Patient-Food Isolate Patterns S P F F P F F S P F F P F F S Asc I Apa I Asc I P= Patient isolate pattern F= Food isolate pattern; S=Standard (H2446)
Asc I Apa I Dendrogram showing 186 isolates patterns collected July 1 through Nov. 30, 2002. Apa I pattern for Asc I outbreak is shown on the right. Outbreak associated PFGE profile: Asc I; Apa I: GX6A16.0235; GX6A12.0003
PulseNet: Future Improvements � Achieve real-time subtyping and real-time communication � Reduce the time it takes for isolates to go from clinical lab to the state/local public health lab � Reduce the time for PFGE testing of isolates � Critical for timely detection of clusters � Timely assignment of PulseNet designations for PFGE patterns � Strengthen collaborations with food industry
Conclusions � PFGE is a valuable part of epidemiologic and environmental investigations � It allows separation outbreak from sporadic cases � Identify cases that are likely to be linked � Help trace source of contamination
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