Surveillance for Zika virus infection among asymptomatic returning travelers from the Rio Olympic and Paralymic Games

Abstract

Background: Zika virus (ZIKV) is an emerging human-pathogenic flavivirus that is associated with congenital malformations in infected fetuses and occasionally severe neurological complications in infected adults. Most (up to 80%) ZIKV-infected patients, however, are asymptomatic or mildly symptomatic, making control of the epidemic more difficult. Moreover, ZIKV can be transmitted by not only by mosquitoes, but via non-vector-borne routes, such as sexual transmission and blood transfusion. The risk of dissemination of ZIKV among asymptomatic returning travelers from the Rio Olympic and Paralympic Games was unknown. Methods: The study was approved by the Institutional Review Board of The University of Hong Kong / Hospital Authority Hong Kong West Cluster. Voluntary testing for anti-ZIKV antibody and viral shedding in bodily fluids (blood, urine, and/or semen) were offered to asymptomatic travelers who have returned from the Rio Olympic and/or Paralympic Games to Hong Kong and/or their sexual partners, starting on 15 days to 6 months after their return. Results: Between 23 August 2016 and 26 October 2016, 203 asymptomatic adult returning travelers joined the study. Their median age was 34 years. Only a minority (<10%) of subjects reported having mosquito bites and none had sexual activity during their stay in Brazil. Most of them (>80%) had applied anti-mosquito measures, including DEET-containing mosquito repellents. Overall, 200 serum, 198 urine, and 41 semen samples were collected. None of these 439 samples was positive for ZIKV RNA by real-time polymerase chain reaction targeting the envelope gene of ZIKV. Immunofluorescent antibody (IgG) was positive in 10 serum samples. All of these 10 patients received yellow fever vaccination before attending the Rio Olympic and/or Paralympic Games. Conclusions: There was no laboratory-confirmed case of ZIKV infection identified among the returning travelers from the Rio Olympic and/or Paralympic Games in this study. These data might suggest that the overall risk of acquiring ZIKV infection was low if appropriate preventive measures were implemented. Similar studies with more subjects should be considered for other mass gathering events in ZIKV-endemic regions to better characterize the risk of acquiring ZIKV infection during these events and the effects of these preventive measures.