Risk of travel-related cases of Zika virus infection is predicted by transmission intensity in outbreak-affected countries

Abstract

BackgroundZika virus (ZIKV) infection is emerging globally, currently causing outbreaks in the Caribbean, and Central and South America, and putting travellers to affected countries at risk. Model-based estimates for the basic reproduction number (R 0) of ZIKV in affected Caribbean and Central and South American countries, obtained from 2015 to 2016 human case surveillance data, were compared by logistic regression and Receiver-Operating Characteristic (ROC), with the prevalence of ZIKV-positive test results in Canadians who travelled to them.ResultsEstimates of R 0 for each country were a good predictor of the ZIKV test result (ROC area under the curve = 0.83) and the odds of testing positive was 11-fold greater for travellers visiting countries with estimated R 0 ≥ 2.76, compared to those visiting countries with R 0 < 2.76.ConclusionsRisk to travellers varies widely amongst countries affected by ZIKV outbreaks. Estimates of R 0 from surveillance data can assist in assessing levels of risk for travellers and may help improve travel advice. They may also allow better prediction of spread of ZIKV from affected countries by travellers.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-1977-z) contains supplementary material, which is available to authorized users.

Travel-related Zika virus cases in Canada: October 2015–June 2017

“…Data suggests that sexual transmission alone is not likely to independently sustain an outbreak (30), and ongoing transmission is unlikely in the absence of tropical/subtropical Aedes spp. (32). The primary mosquito vectors-Aedes aegypti and Aedes albopictus-are not established in Canada and current research suggests that Canadian mosquito species are not competent hosts.…”

“…It has been previously reported that the risk to travellers varies with the force of transmission cycles in the countries they are visiting, and that travellers as a group are not highly protected from infection in affected countries by virtue of their traveller status (32). The peak in cases recorded in July and August of 2016 was due to increases in cases exposed in Central America and the Caribbean, and to some extent from Mexico, but at a time when travel to these destinations are typically at their seasonal lows.…”

Consensus and conflict among ecological forecasts of Zika virus outbreaks in the United States

“…But a more detailed epidemiological link is needed between traveler force of infection and the scale of subsequent local outbreaks; so far, that causation has only been investigated in reverse. 44 The role of sexual transmission also requires deeper investigation. Early work suggested sexual transmission might be a substantial factor explaining the explosive South American outbreak 45,46 , but recent work has suggested sexually-transmitted outbreaks are unlikely 47 , even if sexual transmission increases the severity of vector-borne outbreaks 48 ; others still argue these risks are "understated."…”

Risk assessment strategies for early detection and prediction of infectious disease outbreaks associated with climate change

“…Refugees, often from geographical areas where infectious diseases are more common and with different vaccination schedules and practices, may inadvertently bring these diseases into Canada (12). Tourism is also affected by climate change, as changes in both home and travel destinations influence the push and pull of factors motivating people to travel and the potential for disease spread (13)(14)(15). Vectors and pathogens can inadvertently be transported through shipments by air, land and sea (16)(17)(18).…”

“…Air travel has also been responsible for travellers carrying infections into new areas. In Canada, returning travellers have brought with them the Zika virus and have also sparked an outbreak of severe acute respiratory syndrome (SARS) coronavirus (15,21,22).…”