Title : Chikungunya and zika high-risk co-occurrence clusters in Brazil: Is there a perfect overlap?
Chikungunya and Zika diseases are transmitted by the same vectors, Aedes aegypti and Ae. albopictus, and possibly the transmission is related to the same environmental and socioeconomic factors. In other words, a simultaneous space and time occurrence is expected. In addition, these arboviruses have similar signs and symptoms, making clinical and laboratory diagnosis difficult. Consequently, the simultaneous circulation of these diseases can impact the overload of assistance services. The Pan American Health Organization and the Brazilian Ministry of Health have warned of an increase in the number of chikungunya and Zika cases and death in America and Brazil above those reported in recent years, 2019-2023. This study aimed to do scan multivariate analyses and find high-risk temporal, seasonal, space, and space-time clusters for the Zika and chikungunya co-occurrence in Brazilian municipalities between 2015 and 2021. We used the municipality of residence, age group, sex, symptom onset month, and year of the Zika and chikungunya confirmed cases. We also considered the centroid coordinates and population of the municipalities, and a significance level of 5%. The purely temporal analysis revealed a high-risk co-occurrence cluster between January and May 2016. Seasonal analysis revealed a high-risk cluster between January and June, during summer and autumn. The spatial analyses identified 20 clusters, including 103 municipalities in the central-west Brazilian region, 63 in the southeast, 11 in the north, eight in the northeast, and one in the south. The space-time analysis revealed 13 high-risk clusters, including 803 municipalities in the northeast, 146 in the north, 41 in the southeast, two in the south, and, contrary to the spatial analysis, none in the central-west. Most of these clusters began between January and April, from 2015 to 2017, except one that began in November 2015 (in the northeast) and three that started in 2021 (two in the northeast and one in the south). The spatial and space-time clusters with the highest relative risk for chikungunya and Zika co-occurrence happened in Bahia state. Despite some common areas, we observed the absence of a perfect overlap between spatial and space-time clusters for Zika and chikungunya in the present study. One hypothesis for these patterns includes the degree of susceptibility of populations in different Brazilian regions. Furthermore, this may also be related to socioeconomic factors, which were more associated with chikungunya than Zika, making their spatial pattern unequal. Other studies have indicated that vector differences, virus genetic mutation, and precipitation levels may influence the distribution pattern for each disease. In conclusion, we observed a dispersion of arboviruses from northeast to central-west, first for Zika in 2016 and chikungunya in 2018; their resurgence in the northeast in 2021; and the same seasonality. Identifying the high-risk areas of co-occurrence is essential to alert the health services to avoid a system collapse.
Financial support: FAPESP (grant number 2021/10212-1, 2021/11721-7, 2020/12371-7, 2020/01596-8) and CNPq (PQ-1C, 304391/2022-0).
Audience take away:
- Temporal, seasonal, space, and space-time multivariate cluster analyses of the co-occurrence of Zika and chikungunya in Brazil between 2015 and 2021.
- Simultaneous temporal and seasonal analyses.
- Spatial clusters were not perfectly overlapping, however presented an area in common.
- High-risk space-time clusters was found in the central-west region, but not in the same period.
- Resurgence of Zika and chikungunya cases in the northeast Brazilian region in 2021.