Subnational Heterogeneity in RSV Seasonality in Tropical Colombia, 2022–2024

Background RSV transmission in tropical settings is often assumed to occur year-round, and preventive strategies are frequently recommended accordingly. However, sub-national variation in epidemic timing remains incompletely characterized. Granular local surveillance data may help refine timing of prevention, particularly in resource-limited settings prioritizing high-risk populations. Methods We analyzed aggregated RSV surveillance data from the Viral Respiratory Infection Surveillance Network (VIRAL Network LATAM–Colombia) across epidemiologic weeks 1–52 during 2022–2024. Data were obtained from 15 centers in seven climatically diverse cities spanning sea level to 2,640 m altitude. City-specific percentile thresholds were used to define transmission intensity. Epidemic patterns were categorized as concentrated, prolonged, or bimodal, and inter-city synchrony was assessed using pairwise Spearman correlations. Results Among 39,505 multiplex respiratory panels, 6,699 (17.0%) were RSV-positive. RSV was detected year-round in all cities, with off-season detections accounting for 16.2%–64.5% of annual cases. Five cities exhibited a synchronized epidemic corridor between March and July with high temporal concordance (all pairwise ρ ≥0.71, P < .01). Cartagena showed delayed coastal transmission, while Cúcuta demonstrated bimodal circulation with attenuated seasonality. Overall, two cities met criteria for concentrated transmission, four for prolonged transmission, and one for bimodal patterns. Conclusions Although RSV circulated throughout the year, epidemic activity converged temporally across most Colombian cities, with notable sub-national heterogeneity. These findings suggest that improved understanding of local epidemic timing could support geographically tailored implementation of RSV preventive strategies.