A cross-sectional analysis of Zika virus infection in symptomatic and asymptomatic non-pregnant travellers: Experience of a European reference center during the outbreak in the Americas.

BACKGROUND: Zika virus (ZIKV) infection a concern to travellers because of potential sexual transmission and adverse pregnancy outcomes. OBJECTIVE: To describe our experience in diagnosing ZIKV in travellers returning from endemic territories. METHOD: Travellers were evaluated for ZIKV at our clinic in a 12-month period during the outbreak, using ZIKV-specific RT-PCR and anti-ZIKV Immunoglobulin M/G ELISA when symptomatic, and ELISA only for asymptomatic travellers, preferably from 20 days after the last exposure. All positive ELISA results were subject to confirmation by Virus Neutralization Testing. We estimated post-test probabilities of ZIKV in asymptomatic travellers. RESULTS: Of 462 travellers, 227 reported symptoms and 235 did not. Asymptomatic travellers had similar baseline characteristics, but were younger (median age 31 vs. 33 years, p = 0.01) and had reproductive concerns more often (75.8% vs. 24.2%). ZIKV infection was confirmed in 49 cases: 46/227 (20.3%) were symptomatic and 3/235 (1.3%) asymptomatic. Rash (positive likelihood ratio (LRP) 5.6) and conjunctivitis (LRP 10.8) predicted ZIKV infection. The post-test probability of a negative ELISA-result at 20-25 days was below 0.1%. CONCLUSION: ZIKV infection was frequent in symptomatic, but not in asymptomatic travellers. We consider negative ELISA results at 20-25 days after exposure a safe strategy to rule out ZIKV infection. Testing for ZIKV-specific antibodies within this timeframe could be particularly valuable in the management of returning travellers who wish to conceive.

Incidence of Zika virus infection in a prospective cohort of Belgian travellers to the Americas in 2016.

BACKGROUND: The incidence rate of Zika virus (ZIKV) infection in travellers from non-endemic areas to the Americas during the ZIKV outbreak in 2016 is unknown. METHODS: Belgian adults who planned to travel to South America, Central America, and the Caribbean were recruited prospectively to study the incidence and characteristics of ZIKV. Demographic data and sera were collected at baseline. Participants were trained 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 travellers, obtained at least 20 days post travel, were tested by 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, with a median age of 32 years (range 19-64 years). Travel destinations were countries in South America (n=20), Central America (n=24), and the Caribbean (n=5). The total travel duration was 67.8 person-months. Illness was reported by 24 participants (49.0%). ZIKV infection was confirmed in nine cases, by RT-PCR (n=5) and by VNT (n=4). Only one of nine ZIKV cases (11.1%) was asymptomatic. The ZIKV incidence rate was 17.0% (95% confidence interval 7.8-32.2%) per month of travel. CONCLUSIONS: The ZIKV incidence rate in adult travellers from non-endemic countries to the epidemic territories during the 2016 outbreak was high. Asymptomatic ZIKV infection was rare in this population.