Changing Patterns of Pertussis in a Children's Hospital in the Polymerase Chain Reaction Diagnostic Era.

Abstract

To assess changes in diagnostic practice and vaccine schedules for pertussis, we used culture-confirmation and clinical severity to compare pertussis cases at a single Australian tertiary pediatric hospital during relevant periods. We replicated the case ascertainment methods of a study reporting a 2-year epidemic period 1997-1999 (whole cell pertussis vaccine with 18-month booster, only culture available) to conduct a retrospective cross-sectional observational study over a 6-year period 2007-2012 (acellular pertussis vaccine, no 18-month booster, polymerase chain reaction and culture available). Cases were compared from case note review 2007-2012 (including prevalence of comorbidities) and published data 1997-1999. During 2007-2012, average annual hospitalizations in those aged < 6 months increased 2.3-fold (32.0 vs 14.0) and in those aged > 6 months by 5.1-fold (17.7 vs 3.5). Limited to culture-positive hospitalizations, there was no increase in those aged < 6 months (14.0 vs 14.5) contrasted with a 4.6-fold increase in those aged > 6 months (2.3 vs 0.5), despite increased annual culture requests (488 vs 188). In 2007-2012, significant comorbidities were documented in 41/72 (57%) hospitalized children aged ≥ 12 months vs 38/225 (17%) <12 months (OR 6.5, 95% CI 3.7-11.7). Increased cases of culture-positive hospitalized pertussis were limited to fully immunized children > 6 months of age, consistent with schedule changes. Significant comorbidities were common, making a booster dose at 12-18 months of age especially important.