Seasonal distribution of pertussis

Introduction/Objective. The seasonality of pertussis is not exactly determined. The aim of this study was to describe the seasonal distribution of pertussis in the South Bačka District of Vojvodina, Serbia, during four consecutive years. Methods. Data for this observational study were obtained from outpatient and inpatient health care facilities in the South Bačka District from January 1, 2013 to December 31, 2016. We evaluated the seasonal distribution of pertussis among the patients who fulfilled one or more criteria of clinical case definitions of pertussis proposed by the Global Pertussis Initiative. Laboratory confirmations of pertussis were obtained using real-time polymerase chain reaction or ELISA serology tests. Results. A total of 1,043 participants were included, of which 28.8% were laboratory-confirmed pertussis, with the highest prevalence of laboratory confirmation (66%) in June 2016. Observed by seasons (spring, summer, fall, and winter), there was no significant difference in the average number of testing patients or laboratory-confirmed pertussis during the study period. The average number of laboratory-confirmed cases was significantly higher in patients 0–6 years of age (p = 0.020), and with a borderline of significance in the 7–10 years age group (p = 0.049) in summer, compared to other three seasons during four consecutive years. Conclusions. With the increased physician awareness after implementation of the new clinical case definitions, pertussis was recognized throughout all four consecutive years without a clear seasonal pattern of occurrence in our area. Paralleling increase of laboratory-confirmed pertussis during summer months in comparison with other seasons in younger and older age groups suggests a possible transmission within families