Diagnostic Performance and Clinical Outcomes of Pertussis in Hospitalized Children in Relation to Available Vaccination Status: A Retrospective Cohort Study.

Introduction: Bordetella pertussis infections have resurged globally, posing notable public health challenges, particularly in pediatric populations. Poland remains the only EU country that continues to use the whole-cell pertussis vaccine (wP) in routine immunization. This study evaluated the vaccination status and diagnostic value of available testing modalities in relation to the clinical presentation and management of pertussis in pediatric patients.

Methods: A retrospective cohort study of 269 children was conducted between January and December 2024. Patients with B. pertussis infection confirmed by real-time polymerase chain reaction (PCR; PCR-Fluorescence Probing Kit, Sansure, China) and/or serological testing (NovaLisa B. pertussis ELISA, Gold Standard Diagnostic, Germany) were included. Clinical characteristics and vaccination histories of confirmed cases were obtained from electronic medical records and telephone interviews with parents.

Results: Pertussis was laboratory-confirmed in 76 of the 269 tested children (28%). PCR accounted for the majority of laboratory-confirmed cases and remained positive in some children during the fifth and sixth week of coughing. The highest proportion of cases was observed in infants under 1 year of age (n = 25, 32.9%). In older age groups, the proportion of cases reached 17% in children aged 1-5 years, 19% in those aged 6-11 years, and 10% in children aged 12-15 years. Adolescents over 15 years of age accounted for only two cases (2.6%). Twelve patients met criteria for severe pertussis (PSS > 5), which occurred in both vaccinated and unvaccinated children. The interval between disease onset and the last vaccine dose ranged from 1 month to 12 years, and a trend toward more pronounced clinical manifestations with longer time since the last booster was observed. No differences in clinical symptoms were found between children vaccinated with wP and acellular (aP) vaccines.

Conclusions: The occurrence of cases several years after vaccination highlights the importance of continued surveillance to strengthen pertussis prevention strategies. Pertussis cases occurring within 5 years of wP vaccination warrant further population-based and molecular studies to evaluate potential factors such as waning immunity or antigenic changes in circulating B. pertussis strains.