[Epidemiological characteristics and hospitalization status of pertussis in Zhejiang Province, 2024]

Objective: To describe the epidemiological characteristics and hospitalization status of pertussis in Zhejiang Province in 2024. Methods: Individual data on pertussis cases reported in Zhejiang Province from January 1 to December 31, 2024, and their diphtheria, tetanus, and pertussis (DTP) vaccination records were collected from the China Disease Prevention and Control Information System and the Zhejiang Provincial Intelligent Service Information System on Immunization Program. Descriptive epidemiological methods were used to analyze the epidemiological characteristics and hospitalization status of cases. The Cochran-Armitage trend test was employed to examine the trend in hospitalization rates with increasing number of DTP vaccine doses, and a multivariate logistic regression model was further used to explore the association between the number of DTP vaccine doses and the hospitalization rate of pertussis. Results: A total of 59 917 pertussis cases were reported in Zhejiang Province in 2024, with an annual reported incidence rate of 90.42 per 100 000 population, representing an increase of 37.64 times compared with 2023 (2.34 per 100 000). The cases were distributed across a wide age range, with the highest proportion (63.00%) occurring in the 5-9 years age group. Among the 2 830 cases aged <1 year, the highest proportion (42.76%) was observed in infants aged 3-5 months. Among the 7 826 cases reported after July 1, 2024, 1 513 (19.33%) were hospitalized, including 1 507 general hospitalizations and 6 intensive care unit (ICU) admissions. Among the ICU cases, 5 cases were aged <1 year. The hospitalization rate of pertussis differed significantly across age groups (P<0.001), with the highest rates observed in those aged ≥81 years (77.27%), 71-80 years (62.50%), and <1 year (56.20%), and the lowest rate in those aged 31-40 years (5.78%). The Cochran-Armitage trend test showed that as the number of DTP vaccine doses increased, the hospitalization rate of pertussis exhibited a decreasing trend (Z=-20.33, P<0.001). Multivariate logistic regression analysis revealed that after adjusting for age and sex, each additional dose of DTP vaccine was associated with a 25% reduction in the risk of hospitalization (aOR=0.75, 95%CI: 0.69-0.80). Conclusion: The reported incidence of pertussis in Zhejiang Province increases substantially in 2024, with school-aged children aged 5-9 years being the main affected population. Infants aged <1 year and elderly individuals are at higher risk of hospitalization after onset, and completing more doses of DTP vaccination can reduce the risk of hospitalization.