Pertussis resurgence in Toronto, Canada: a population-based study including test-incidence feedback modeling

Abstract

BackgroundPertussis 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.MethodsData 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.ResultsFrom 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.ConclusionsToronto'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.

Characterization of co-purified acellular pertussis vaccines

“…1,3 However, since WPVs were replaced by purified APVs in many developed countries in 1980s/1990s, a resurgence of pertussis has been observed in these countries with high vaccination coverage in the past 10 y 11,[19][20][21] The incidence of pertussis among children who were born and vaccinated during the transition to purified APVs have found that the rate of infection is significantly higher among children who have been vaccinated with only APVs compared with those who have been vaccinated with even a single dose of the WPVs. 22 In contrast, in countries where co-purified APVs are used in the national immunization program e.g., Japan and China, the accumulating epidemiological evidence suggests that co-purified APVs may be achieving more consistent population protection, in fact a lower pertusiss incidence is noted in China according to the official report.…”

Effectiveness of pertussis vaccination and duration of immunity

“…The laboratory methods have been previously described. [15][16][17] Briefly, until May 28, 2012, primers targeting the insertion sequence IS481 were used to detect B. pertussis. Following this date, primers targeting a 50-base pair segment of the recA gene were also included to distinguish B. pertussis from Bordetella holmesii.…”

In Search of Factors Negatively Affecting Vaccine Immunity to Pertussis in Preschool Children Before the Administration of the First Booster

“…A different situation was noted in the United States where from 2004 to 2010 over 90% of severe complications and deaths recorded due to pertussis concerned infants ≤ 3 months old [14][15][16][17].…”