LATEBREAKER
Methods/Statistics
A joint analysis of simultaneous epidemics of dengue, chikungunya, and Zika in Colombia using a Poisson-multinomial spatial model Laís Picinini Freitas* Laís Picinini Freitas Alexandra Schmidt Jorge Emilio Salazar Flórez Brayan Ávila Monsalve César García-Balaguera Berta N. Restrepo Gloria I. Jaramillo-Ramirez Mabel Carabali Kate Zinszer
Dengue, chikungunya, and Zika are Aedes-borne diseases (ABD) that have caused large syndemics in the Americas in the 2010s. Colombia, where dengue is historically endemic, faced its first chikungunya and Zika epidemics in 2014 and 2015, respectively, when cases of dengue were also on the rise. In this ecological study, we applied a Poisson-multinomial spatial model to study simultaneously the outbreaks of dengue (n=291820), chikungunya (n=75913), and Zika (n=72031) in Colombian municipalities (n=1121). We obtained case data from the Colombian National Surveillance System (SIVIGILA) by municipality between weeks 01/2014 and 39/2016. The total number of ABD cases is fitted to a Poisson model and, conditioned on the total, we assume a multinomial model for the allocation of the number of cases of each disease across the municipalities. The model also estimates the associations with environmental and socioeconomic variables. Covariates were standardized and the model was fitted using the Stan platform in R. Mean temperature was identified as the main contributor for total ABD cases (mean 2.15, 90%CredI 1.95-2.38). Municipalities with better access to healthcare had an increased risk of ABD (1.20, 1.11-1.30). The Normalized Difference Vegetation Index (NDVI) was also positively associated with the total number of ABD (1.28, 1.18-1.39). However, the odds of a municipality having chikungunya and/or Zika compared to dengue decreased when NDVI increased (0.75, 0.67-0.84, and 0.85, 0.75-0.96, respectively). Increased odds of having chikungunya and/or Zika compared to dengue were observed in more humid municipalities (1.13, 1.01-1.25, and 1.40, 1.26-1.57, respectively). When chikungunya and Zika emerged in Colombia, dengue was widespread in the country. Chikungunya and Zika first epidemics may have concentrated in municipalities with more favorable conditions to the vector, potentially explaining the difference in factors associated with these diseases compared to dengue.