Chikungunya em Fortaleza: padrões epidemiológicos, espaciais e temporais em anos epidêmicos e não epidêmicos (2016-2022)

Abstract

Introduction: Chikungunya is an arboviral disease transmitted by Aedes aegypti that has caused major epidemics in the Americas. Fortaleza (Brazil) stands out as one of the few cities on the continent to register outbreaks in consecutive years, an uncommon occurrence. The capital city is consolidating itself as one of the main epicenters of the disease, with one of the highest case and death burdens ever recorded in the Americas. Objectives: To characterize the epidemiological, temporal, and spatial patterns of chikungunya during epidemic and non-epidemic periods in the municipality of Fortaleza, 2016-2022. Methods: The study comprised three substudies: Substudy 1 - Temporal Trend Analysis: We employed a segmented linear regression to identify the inflection points in the incidence time series through the calculation of the weekly percentage (WPC) with 95% confidence interval. Data were organized in three periods: epidemic (2016-2017), inter-epidemic (2018-2021) and epidemic (2022). Statistical significance was tested using Poisson model with 4,499 Monte Carlo replications (p<0.05). Substudy 2 - Spatial Distribution Analysis: We employed three complementary methods: (a) local empirical Bayesian smoothing; (b) spatial autocorrelation; (c) spatial scan. Units of analysis: 4,422 census sectors in the municipality. Substudy 3 - Spatio-Temporal Analysis: We applied a retrospective spatio-temporal Scan statistics. For this analysis, we used the Notification of Diseases Information System as the data source. We included all cases confirmed by either a laboratory test or clinical-epidemiological criteria. Results: Between 2016 and 2022, Fortaleza recorded 100,142 confirmed cases of chikungunya. Temporal analysis revealed a cyclical pattern, with two major epidemic peaks (2016–2017 and 2022) and an inter-epidemic period (2018–2021) of low transmission, but with residual viral persistence. Spatial analysis revealed a heterogeneous distribution, with the formation of persistent high-risk clusters in the central, southwest, and west regions, coinciding with areas of higher population density and socio-environmental vulnerability. In the first epidemic wave (2016-2017), Bayesian smoothing indicated an average incidence of 1,517.7 cases/100,000 inhabitants, and the Local Moran's I index identified 284 high-high sectors (6.4%), while spatial scanning detected 20 significant clusters, the main one with 43,540 cases, relative risk (RR) = 2.29. During the inter-epidemic period, even with reduced incidence, 349 sectors (7.9%) remained classified as high-high, reflecting the maintenance of critical micro-territories. In 2022, expansion and fragmentation of outbreaks were observed, with 19 statistically significant clusters (RR=2.13–3.46) and the emergence of new transmission points in the northwest and peripheral regions, evidencing the reactivation of historical areas and propagation to border zones. The spatio-temporal analysis reinforced this continuity, showing the persistence of clusters over time, with a progressive shift of transmission from central areas to the peripheries and the maintenance of stable high-risk nuclei in densely populated micro-territories. Conclusions: Chikungunya in Fortaleza reflects a persistent urban transmission model, sustained by structural vulnerabilities and the continued presence of the vector in densely populated areas. The study highlights the importance of territorial and continuous surveillance, supported by spatio-temporal analyses, to anticipate risks and guide interventions. Mitigating the risk of transmission requires structural intersectoral actions focused on sanitation, housing, and environmental management, capable of reducing inequalities and preventing the re-emergence of outbreaks in large tropical urban centers.