Abstract Background: Zika virus (ZIKV) is a mosquito-borne virus that is also transmitted sexually, however, the epidemiological relevance of ZIKV sexual transmission in endemic regions is unclear. Methods: We performed a household-based serosurvey in Northeast Brazil to evaluate the differential exposure to ZIKV and chikungunya virus (CHIKV) among households. Individuals who participated in our previous arboviral disease cohort (indexes) were re-contacted and enrolled, and their household members were newly enrolled. Results: The Relative Risk (RR) of sexual partners being ZIKV seropositive when living with a ZIKV-seropositive index participant was significantly higher, while this was not observed among non-sexual partners of the index. For CHIKV, both sexual and non-sexual partner household members living with a CHIKV-seropositive index had a significantly higher risk of being seropositive. In the non-index based dyadic and generalized linear mixed model analyses, the odds of sexual dyads having a concordant ZIKV PRNT result was significantly higher. We have also analyzed retrospective clinical data according to the participants' exposure to ZIKV and CHIKV. Conclusion: Our data suggest that ZIKV sexual transmission may be a key factor for the high ZIKV seroprevalence among households in endemic areas and raises important questions about differential disease from the two modes of transmission. Keywords: Zika; arbovirus; chikungunya; epidemiology; mosquito; sexual transmission.

3rd November 2020 • comment