BACKGROUND: The incidence rate of Zika virus (ZIKV) infection in travelers from non-endemic areas to the Americas during the ZIKV outbreak in 2016 is unknown.
METHODS: We prospectively recruited Belgian adults, who planned to travel to South America (SAM), Central America (CAM) and the Caribbean (CAR), to study the incidence and characteristics of ZIKV. We collected demographic data and sera at baseline. We trained participants to collect capillary blood on filter paper (BFP). When ill during travel, the participants completed a questionnaire and they sampled BFP for post-hoc analysis. All symptomatic participants were screened for ZIKV using ZIKV-specific RT-PCR on serum or urine, or BFP, and antibody detection assays (ELISA). Follow-up sera of asymptomatic travelers, obtained at least 20days post-travel, were tested with ZIKV ELISA only. All positive ELISA results were subject to confirmation by Virus Neutralization Testing (VNT).
RESULTS: Forty-nine participants completed follow-up, 38 women and 11 men, age 32 years (median, range 19-64). Travel destinations were countries in SAM (n=20), CAM (n=24) and CAR (n=5). The total travel duration was 67.8 person-months. Illness was reported by 24 participants (49.0%). ZIKV infection was confirmed in 9 cases, by RT-PCR (n=5) and by VNT (n=4). Only one of 9 ZIKV-cases (11.1%) was asymptomatic. The ZIKV incidence rate was 17.0% (95%CI [7.8-32.2]) per month of travel.
CONCLUSIONS: The ZIKV incidence rate in adult travelers from non-endemic countries to the epidemic territories during the 2016 outbreak was high. Asymptomatic ZIKV infection was rare in this population.