Epidemiological Distribution and Factors Associated with Bordetella pertussis Infection Among Probable Pertussis Cases in Mexico, 2024–2025

Background: Pertussis has reemerged in several countries, including Mexico. Limited information is available on the demographic and clinical-epidemiological factors associated with Bordetella pertussis infection. Objective: To identify demographic and clinical-epidemiological factors associated with Bordetella pertussis RT-qPCR positivity among probable pertussis cases in the Mexican Social Security Institute (IMSS) surveillance system. Materials and Methods: A nationwide retrospective analytical cross-sectional study was conducted. Probable pertussis cases with a valid RT-qPCR result between January 2024 and 31 July 2025 were included. The distribution of cases was described, and overall positivity as well as positivity according to demographic, temporal, and geographic characteristics were estimated. Bivariate analysis and unconditional binary logistic regression were performed to estimate odds ratios (ORs), adjusted odds ratios (aORs), and 95% confidence intervals (95% CIs) for factors associated with RT-qPCR positivity among probable pertussis cases. Results: A total of 2153 probable pertussis cases were included, of whom 266 tested positive for Bordetella pertussis (overall positivity: 12.4%). Infants younger than one year accounted for 55.3% of positive cases. In the multivariable analysis, infants younger than one year had higher odds of RT-qPCR positivity than those aged 15–24 years (aOR = 2.12; 95% CI: 1.20–3.77). An association with summer symptom onset was also observed in the primary analysis; however, this finding was not consistently statistically significant across the restricted observation periods Conclusions: Among probable pertussis cases evaluated through the IMSS surveillance system during 2024–2025, RT-qPCR positivity was particularly concentrated among infants younger than one year. These findings highlight the importance of strengthening epidemiological and laboratory surveillance, particularly among infants, to support timely case detection and public health interventions.