Environmental and Climatic Risk Factors for Zika and Chikungunya Virus Infections in Rio de Janeiro, Brazil, 2015–2016

BACKGROUND: The objective of the present study was to identify drivers of the ZIV epidemic in the state of Rio de Janeiro to predict where the next hotspots will occur and prioritize areas for vector control and eventual vaccination once available. METHODS: To assess climatic and socio-economic drivers of arbovirus epidemics, we mapped rainfall, temperature, and sanitation infrastructure in the municipalities where individuals with laboratory confirmed cases of arboviral infection resided using our spatial pattern risk model. RESULTS: From March 2015 to May 2016, 3,916 participants from 58 municipalities in the state of Rio de Janeiro were tested for dengue, Chikungunya (CHKV), and ZIKV by RT-PCR and enzyme immunoassays. During the same period, 69,256 suspected cases of dengue, CHKV, and ZIKV were reported to the Rio Health Department, including 23,983 of dengue, 44,572 of ZIKV, and 701 of CHKV. Laboratory confirmed cases included 29 cases (0.7%) of dengue, 1,717 of ZIKV (43.8%), and 2,170 of CHKV (55.4%). Rains in Rio began in October 2015 and were followed one month later by the largest wave of the ZIKV epidemic (Figure 1). ZIKV cases markedly declined in February 2016, which coincided with the start of a CHKV outbreak. Rainfall predicted ZIKV and CHKV in Rio with a lead-time of 3 weeks each time. Social and environmental variables predicted the number of cases. The temporal dynamics of ZIKV and CHKV in Rio de Janeiro are explained by the shorter incubation period of the viruses in the mosquito vector; 2 days for CHKV vs 10 days for ZIKV. CONCLUSION: The association between rainfall and ZIKV reflects vector ecology, as the larval stages of Aedes aegypti require pools of water to develop. Rainfall in October 2015 would have produced such pools resulting in increased mosquito abundance likely contributing to the ZIKV epidemic in humans the following month. The decrease in ZIKV in February 2016 and the increase in CHKV likely arose due to within-vector competition. The Pan American Health Organization’s ZIKV Strategic Plan states that controlling arboviruses requires mapping their social and environmental drivers. Our findings contribute to such control efforts. DISCLOSURES: All authors: No reported disclosures.