The 2024-2025 Pertussis outbreak in children in Chengdu: A large-scale retrospective cross-sectional study.

Abstract

To characterize the epidemiological features of pertussis among pediatric patients tested by polymerase chain reaction (PCR) at a tertiary children's hospital in Chengdu from May 2024 to April 2025, with particular emphasis on temporal variation and age distribution, to inform regional prevention strategies. This retrospective cross-sectional study included 19,084 pediatric patients who underwent PCR testing for Bordetella pertussis. Multivariable logistic regression and subgroup analyses were used to examine associations between PCR positivity and season, age group, sex, and visit type. The overall PCR positivity rate was 20.47% (3,905/19,084). Summer had the highest positivity rate (25.62%) and accounted for the majority of positive cases (67.12%, 2,621/3,905), followed by spring (21.50%; 23.58% of cases, 921/3,905). The monthly number of positive cases peaked in June 2024 (n = 1,078). School-aged children (6 to <12 years) represented the largest proportion of positive cases (56.72%, 2,215/3,905) and had significantly higher PCR positivity than other age groups (χ² = 1098.21, df = 4, P < 0.001). In multivariable analysis, school-aged children had higher odds of PCR positivity than adolescents (adjusted OR = 1.55, 95% CI 1.23-1.95). No significant association with sex was observed. Outpatients showed higher PCR positivity than inpatients (21.41% vs. 13.66%; crude OR = 1.72, 95% CI 1.52-1.95, P < 0.001). The outpatient advantage was most pronounced in spring (crude OR = 1.95) and summer (crude OR = 1.44), with a significant interaction by season (P = 0.013). This hospital-based study identified a substantial burden of PCR-confirmed pertussis among symptomatic children in Chengdu during the study period, with a prominent peak from May to July 2024 and the highest positivity among school-aged children. These findings may partly reflect waning vaccine-induced immunity and increased social contact in school settings, and support strengthened surveillance, timely PCR testing, and targeted pertussis prevention strategies for school-aged children.