Front Public Health. 2026 Aug 3;14:1892098. doi: 10.3389/fpubh.2026.1892098. eCollection 2026.
ABSTRACT
BACKGROUND: Acute bronchiolitis, mainly attributed to respiratory syncytial virus (RSV), is the leading cause of infant hospitalization for lower respiratory tract disease worldwide. Nirsevimab and maternal RSVpreF (Abrysvo) confer about 6 months of protection, so timing relative to the season affects their impact. Ecuador spans the equator from sea level to valleys above 4,000 m and is considering introducing these products, yet lacks subnational evidence on the seasonality of bronchiolitis, altitudinal patterning, or post-pandemic stability.
METHODS: We conducted a national ecological time-series analysis of hospital discharges from the Ecuadorian Statistics Institute, 2007-2024 (19,788,097 discharges; 204 of 224 cantons had complete data and formed the analytic panel). The primary outcome was acute bronchiolitis (ICD-10 code J21) in children younger than 12 months (n = 23,190 nationally; 22,724 in the panel), with secondary outcomes across three RSV-relevant age bands, ICD-10 code J21 under 5 years, and two RSV-specific ICD-10 codes (J12.1 and J20.5; 2018-2024). K35 (appendicitis) was a negative control. Analyses combined circular seasonality metrics with block-bootstrap confidence intervals (CIs), year-by-year disaggregation, and complementary sensitivity analyses [Moving Epidemics Method (MEM), Bai-Perron breaks, and lagged climate correlations].
RESULTS: The weighted circular peak month of infant bronchiolitis hospitalizations shifted after the pandemic in Costa (+2.16 months), Sierra (+1.22), and Amazonía (+1.91), attenuating with altitude from +2.19 months below 500 m to +0.88 at 1,500-3,000 m. 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 RSV-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 RSV proxy in both, and the three regional peaks now span 2 months.
CONCLUSION: Bronchiolitis seasonality in Ecuador changed after the pandemic, most clearly and stably in Costa; Sierra showed a transient 2022 perturbation with partial reversion by 2023-2024, and Amazonía’s estimates remained unstable and underpowered. As region-tailored estimates are less stable in Sierra and Amazonía than in Costa, a single national window (nirsevimab February-April; maternal RSVpreF for pregnancies expected to deliver January-May) is a more defensible starting point, pending confirmation from further seasons and, ideally, laboratory-confirmed surveillance.
PMID:42609519 | PMC:PMC13478267 | DOI:10.3389/fpubh.2026.1892098
