Laboratory Testing Recommendations for Zika Virus

Travellers with active symptoms of Zika virus infection

If the symptoms began less than ten days before seeking medical attention, the best test is Zika virus PCR, although serology may also be performed depending on the precise timing of symptoms. A blood and/or urine sample may be requested depending on how long ago the symptoms began. Because the symptoms for Zika virus infections are similar to other diseases transmitted by mosquitoes in the Americas, your doctor will likely also order tests for other infectious diseases such as dengue. This testing recommendation applies to all travellers with active symptoms, including pregnant women.

Travellers with a history of travel to a Zika virus area but no history of symptoms

We know that 75-80% of Zika virus infections occur without symptoms. For these travellers, there is likely no additional benefit to test for evidence of past asymptomatic infection. Should you have questions about this scenario and whether a test would be warranted, you should discuss this with your health care provider. For pregnant patients with a history of travel and no symptoms, see below.

An additional scenario for asymptomatic travellers includes men who have returned from an area with known or suspected Zika virus transmission with either a 1) pregnant partner or 2) partner with whom they are actively trying to conceive a child. Routine testing is not recommended in this context because interpreting the meaning of a negative Zika virus test is difficult is this scenario. For example, depending on the timing of the test, antibodies may not yet have developed in the traveller, making the test result falsely negative. The use of barrier methods (such as condoms) to prevent potential Zika virus transmission for 6 months following return from travel is currently the safest approach. As we learn more about Zika virus and the tests available, this recommendation will be updated as necessary. As every individual situation is unique, we encourage patients facing the above scenario to consult with their health care provider to discuss any special circumstances that might warrant testing.

Special Considerations for Testing of Pregnant Women for Zika Virus

Zika virus infection in pregnancy is also a self-limited disease that lasts a few days up to two weeks. However, there is concern that there may be a risk of microcephaly (abnormally small head size) or abnormal brain development in the fetus. It is unknown at this time whether the timing of the infection in pregnancy (i.e. early versus late) or the severity of the symptoms in the mother have any impact on the chance of the fetus being impacted. Please see below for specific pregnancy-related scenarios. Early consultation with your health care provider regarding questions of Zika virus in pregnancy is recommended for travellers.

Pregnant travellers with active symptoms suggestive of Zika virus infection

Pregnant travellers to areas at risk who develop symptoms of Zika virus infection should seek medical attention. If the symptoms began less than ten days before seeking medical attention, the best test is Zika virus PCR, although serology may also be performed depending on the precise timing of symptoms. Your health care provider should discuss with the local laboratory which test to send, as a blood and/or urine sample may be requested depending on how long ago the symptoms began. Your doctor will likely also order tests for other infectious diseases that are transmitted by mosquitoes in the Americas, such as dengue.

Pregnant travellers with a history of active symptoms compatible with Zika virus that started more than ten days ago

In this context, the Zika virus PCR will likely be negative. Serology for Zika virus would be the most appropriate test. At this time, based on our existing knowledge, pregnant women who developed active symptoms of Zika virus are expected to be most at risk for impact on their fetus. As a result, testing should be offered and consideration given to consulting with an infectious diseases specialist or maternal-fetal medicine specialist.

Pregnant travellers with a history of travel to an area at risk for Zika virus but no history of symptoms

Testing is possible if discussion has occurred between the patient and their health care provider, and they are aware and accepting of the test limitations and that testing may take weeks to complete.

This scenario is the most difficult to navigate in terms of testing. It is estimated that approximately 75-80% of individuals who are infected by the Zika virus never develop symptoms. However, the degree of risk to the fetus following asymptomatic infection in pregnancy is still unknown. In the absence of symptoms, our best Zika virus test (PCR) is unlikely to detect the virus. As a result, serology is the test to consider in this scenario. The use of serology as a screening tool in these instances must be carefully considered, because we do not yet know how well the serology test will perform for these patients.  Furthermore, specific challenges with the test will be the fact that cross-reactions with other related viruses (such as dengue) are common, making the final interpretation of the test difficult.

Women with a history of travel to a Zika virus area who did not develop symptoms of Zika virus but are concerned about their risk of infection, should consult with their health care provider to discuss the testing available as well as its limitations, including the significant questions around the meaning of positive and negative test results. Information around country of travel, mosquito bite exposure, past vaccination history (eg. Yellow fever) and previous travel history to areas where dengue infections are common should be discussed. Information around country of travel, mosquito bite exposure, past vaccination history (eg. Yellow fever) and previous travel history to areas where dengue infections are common should be discussed.