Assessing Zika Risk in International Travelers

Clinicians should discuss destination-specific risks for Zika infection with patients who are international travelers, but providing risk-based guidance can be challenging. Because Zika virus infections are often asymptomatic or result in mild clinical illness, patients may not seek treatment, and cases may go unreported. In addition, countries have different capacities for surveillance, so a lack of reported cases does not necessarily indicate a lack of Zika virus transmission in a particular country. I'm Dr Allison Taylor Walker with the Travelers' Health Branch at the Centers for Disease Control and Prevention (CDC), and today we're going to discuss things to consider in assessing a traveler's risk of becoming infected with Zika at his or her travel destination.

The World Health Organization (WHO) bases its Zika country classifications on what is known about Zika and how it spreads.^[1] The WHO categories can be described as epidemic, endemic, and presumed endemic. Countries with presumed endemic Zika virus transmission include those that have the Aedes species mosquito vector as well as dengue (which is spread by the same mosquito) and share a climate and a border with a country that has previously reported local mosquito-borne transmission of Zika virus. Testing, surveillance, and reporting vary among countries; therefore, CDC recommendations are the same for all countries with known or presumed risk—pregnant women should not travel to these countries, and people who travel to a country with Zika should wait before trying to conceive. Of course, all travelers should take steps to prevent mosquito bites during and after travel.

A clinician counseling a patient who is considering travel to an area with risk for Zika should customize guidance to that particular traveler. CDC offers specific guidance for various situations, including those circumstances when pregnant women or their partners must travel to an area of Zika risk, including precautions to prevent sexual transmission and information on who should be tested.

Travelers will all have their own individual tolerance for risk. What are the trip characteristics that could change the risk of acquiring Zika? Risk increases with increased duration of travel. Seasonality can affect risk if travel is during the warmer and often the rainy months, which may lead to increased mosquito activity. What is the nature of the trip? How willing is the traveler to practice mosquito bite precautions? Some hotels and resorts publicize their mosquito control practices, but how confident is the traveler in those assurances? If a traveler is planning to become pregnant, is she willing to delay pregnancy until 2 months after travel or 6 months if her male partner travels? If the traveler is pregnant, can the trip be postponed until after the baby is born? If a male traveler has a pregnant partner, is he willing to use condoms for the duration of the pregnancy? If a pregnant woman chooses to travel, is the couple prepared for the possibility of a negative pregnancy outcome?

Travelers may be understandably frustrated by the uncertainty in determining their level of risk. We hope that explaining some of the reasons why their individual risk can't be quantified can help them make informed choices with the limited information that's available. More information on areas with risk for Zika, including Zika travel notices, destination pages, and an interactive map of areas where Zika is a risk, are found at https://www.cdc.gov/travel.