Subnational Heterogeneity in Respiratory Syncytial Virus Seasonality in Tropical Colombia, 2022-2024

Respiratory syncytial virus (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.

We analyzed aggregated RSV surveillance data from the Viral Respiratory Infection Surveillance Network (VIRAL Network LATAM-Colombia) across epidemiological weeks 1-52 during 2022-2024. Data were obtained from 15 centers in 7 climatically diverse cities spanning sea level to 2640 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.

Among 39 505 multiplex respiratory panels, 6699 (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 ≥ .71, P < .01). Cartagena showed delayed coastal transmission, while Cúcuta demonstrated bimodal circulation with attenuated seasonality. Overall, 2 cities met criteria for concentrated transmission, 4 for prolonged transmission, and 1 for bimodal patterns.

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.