title: Pertussis resurgence in Toronto, Canada: a population-based study including test-incidence feedback modeling.
abstract: BACKGROUND
  Pertussis continues to challenge medical professionals; recently described increases in incidence may be due to age-cohort effects, vaccine effectiveness, or changes in testing patterns. Toronto, Canada has recently experienced increases in pertussis incidence, and provides an ideal jurisdiction for evaluating pertussis epidemiology due to centralized testing. We evaluated pertussis trends in Toronto using all available specimen data, which allowed us to control for changing testing patterns and practices.
  
  
  METHODS
  Data included all pertussis culture and PCR test records for Greater Toronto from 1993 to 2007. We estimated incidence trends using Poisson regression models; complex relationships between disease incidence and test submission were explored with vector autoregressive models.
  
  
  RESULTS
  From 1993 to 2007, 26988 specimens were submitted for testing; 2545 (9.4%) were positive. Pertussis incidence was 2 per 100,000 from 1993 to 2004 and increased to 10 per 100,000 from 2005-2007, with a concomitant 6-fold surge in test specimen submissions after the introduction of a new, more sensitive PCR assay. The relative change in incidence was less marked after adjustment for testing volumes. Bidirectional feedbacks between test positivity and test submissions were identified.
  
  
  CONCLUSIONS
  Toronto's recent surge in pertussis reflects a true increase in local disease activity; the apparent size of the outbreak has likely been magnified by increasing use of pertussis testing by clinicians, and by improved test sensitivity since 2005. These findings may be applicable to changes in pertussis epidemiology that have been noted elsewhere in North America.
authors: Dalla Lana School of Public Health, University of Toronto, Canada. david.fisman@utoronto.ca
authors: David N
authors: DN
authors: Fisman
authors: Patrick
authors: P
authors: Tang
authors: Tanya
authors: T
authors: Hauck
authors: Susan
authors: S
authors: Richardson
authors: Steven J
authors: SJ
authors: Drews
authors: Donald E
authors: DE
authors: Low
authors: Frances
authors: F
authors: Jamieson
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005246:Feedback; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008499:Medical Records; D008962:Models, Theoretical; D009864:Ontario / Q000453:epidemiology; D016012:Poisson Distribution; D011159:Population Surveillance; D014505:Urban Population; D014917:Whooping Cough / Q000175:diagnosis / Q000453:epidemiology*; D055815:Young Adult