title: Outbreak of atypical pertussis detected by polymerase chain reaction in immunized preschool-aged children.
abstract: BACKGROUND
  From October 2005 to March 2006, a laboratory-confirmed outbreak of pertussis occurred in preschool-aged children (1-4 years) in Toronto, Canada. A case-control study in children was done to identify the risk factors for being positive for Bordetella pertussis by polymerase chain reaction (PCR).
  
  
  METHODS
  A case was defined as an individual 0 to 18 years of age who tested positive for B. pertussis by PCR in Toronto from October 2005 to March 2006. Each case was matched to 2 controls (negative for B. pertussis by PCR) by: (1) age, (2) geographic region of testing, and (3) date of testing.
  
  
  RESULTS
  One hundred eighty-nine cases and 296 controls were enrolled. Only 42% of cases (vs. 25% controls, P < 0.0001) met a clinical definition of pertussis, 3 cases (4 controls) were hospitalized, and the secondary household attack rate was 8%. One-third of cases were positive for another respiratory pathogen and >90% of cases and controls were up-to-date with pertussis immunization. Children attending school (matched odds ratio [ORm] = 5.2; 95% confidence intervals [CI]: 1.4-19.0), day care (ORm = 2.2; 95% CI: 1.2-4.0), visiting a doctor's office (ORm = 1.6; 95% CI: 1.0-2.5), or exposed to a household member (median age: 4-5 years) with a pertussis-like cough (ORm = 1.9; 95% CI: 1.0-3.6) were significantly more likely to have a positive PCR test for B. pertussis.
  
  
  CONCLUSIONS
  The main risk factors for PCR positivity for B. pertussis were school or day care attendance. Atypical symptoms were likely moderated by high immunization rates or may have been caused by other respiratory pathogens. In some cases, a positive PCR result might simply have reflected transient nasopharyngeal carriage of B. pertussis.
authors: Division of Infectious Diseases, Department of Pediatrics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada. valerie.waters@sickkids.ca
authors: Valerie
authors: V
authors: Waters
authors: Frances
authors: F
authors: Jamieson
authors: Susan E
authors: SE
authors: Richardson
authors: Michael
authors: M
authors: Finkelstein
authors: Anne
authors: A
authors: Wormsbecker
authors: Scott A
authors: SA
authors: Halperin
mesh_terms: D001886:Bordetella pertussis / Q000235:genetics / Q000302:isolation & purification*; D002170:Canada / Q000453:epidemiology; D002353:Carrier State / Q000453:epidemiology / Q000382:microbiology; D016022:Case-Control Studies; D002656:Child Day Care Centers; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification*; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000379:methods*; D012307:Risk Factors; D012574:Schools; D014917:Whooping Cough / Q000453:epidemiology* / Q000382:microbiology*
chemical_list: D004269:DNA, Bacterial