Dominance of two genotypes of Bordetella pertussis during a period of increased pertussis activity in Alberta, Canada: January to August 2012

Abstract

Objectives: The purpose of this study was to undertake an epidemiological analysis of an increase in Bordetella pertussis activity during the period January 1 to August 31, 2012 in Alberta, Canada. B. pertussis testing was done using an IS481 real-time PCR assay with PCR-positive and indeterminate specimens cultured and stored for further analysis.

Methods: Laboratory data were linked to Alberta Health (AH) cases that were reported in the Communicable Disease Reporting System (CDRS) to identify case isolates; exclusion criteria were used to avoid biases. Case isolates were analyzed at the National Microbiology Laboratory (NML) by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Pertussis immunization data were extracted from the Alberta Provincial Immunization Repository (Imm/ARI) and linked to the pertussis cases.

Results: Using PFGE and MLST, 52 case isolates could be divided into two main sequence type groups: 41 cases belonged to the ST-1 group (ST-1 and the novel ST-19) and 11 cases belonged to the ST-2 group (ST-2 and the novel ST-20). Of the total cases genotyped (N=52), 18 (34.6%) had a history of immunization, 28 (53.8%) were not immunized, and six (11.6%) had an unknown immunization history. Of the total non-immunized cases, 25/28 (89.2%) belonged to the ST-1 group. Furthermore, of the 41 ST-1 group cases, 25 were not immunized compared to only three of the ST-2 group cases (p=0.0004, Fisher's exact test).

Conclusions: This study shows the dominance of two genotypes of B. pertussis in our jurisdiction and indicates less pertussis immunization in individuals infected with the ST-1 group.

Keywords: Genotype; Immunization; Pertussis; Public health.