Abstract
OBJECTIVE: To provide a surveillance update on overall and age-related pertussis trends in British Columbia (BC), Canada, spanning the 20-year period from 1993-2013. METHODS: Provincial surveillance data for confirmed pertussis cases were extracted from January 1, 1993 to October 31, 2013. Annual and age-specific incidence rates were derived using provincial and regional population estimates. RESULTS: BC experienced substantial pertussis epidemics in the late 1990s and early 2000s with incidence ranging from 20 to 40 per 100,000 overall and peaking in pre-teens aged 10-13 years at >200 per 100,000 during the epidemic of 2000. Overall incidence dropped to historical lows ranging from 1 to 6 per 100,000 between 2005 and 2011. This low-level activity was followed by resurgence in 2012 driven by outbreaks in Lower Mainland regions of BC with overall provincial incidence reaching 10 per 100,000. Age-specific incidence in 2012 was highest among infants <1 year old (64 per 100,000) and children 12-13 years old (56-57 per 100,000), with a shift in the age distribution away from preschool-aged children toward pre-teens and young teens evident since 2000. Adult incidence remained <10 per 100,000 throughout the study period and was 5 per 100,000 in 2012. Year-to-date provincial incidence rates overall for 2013 are 6 per 100,000, with ongoing asynchronous activity observed primarily on Vancouver Island. CONCLUSIONS: Pertussis activity in BC showed expected cyclical fluctuations, with a peak incidence observed in 2012, mostly affecting infants and pre-teens/teens but at lower levels than prior peaks. Following substantial epidemics in the 1990s and early 2000s and the incorporation of acellular pertussis vaccine into the routine immunization program, the immuno-epidemiology of pertussis may still be in transition. Further monitoring and evaluation are needed to guide possible program changes for BC.