Regional, altitudinal, and age-specific heterogeneity of bronchiolitis hospitalization seasonality in Ecuador, 2007-2024, and implications for RSV immunoprophylaxis timing.

Costa was stable across 2022-2024; Sierra and, more so, Amazonía varied widely year to year (Amazonía peak ranged March-July, n = 37-42/year), so the pooled estimate should be read with caution.

The composite respiratory syncytial virus-coded outcome tracked ICD-10 code J21's timing closely in Costa (0.15-month difference) and Sierra (0.40), supporting ICD-10 code J21 as a reasonable respiratory syncytial virus proxy in both, and the three regional peaks now span 2 months.