CDC Updates Zika Testing Guidelines for Pregnant Women

Only 20% of individuals infected with the Zika virus exhibit symptoms, and those who do usually report mild ones, such as a rash or fever. Unfortunately, however, that is not to say that Zika is completely harmless. Infection during pregnancy can cause neurological complications in the fetus. In addition, time of infection can play a role in the development of such complications; fetuses of women who are infected in the first trimester are at greater risk of Zika-related complications.

Today, May 5, 2017, a Health Alert Notice was issued by the Centers for Disease Control and Prevention (CDC), which updates testing guidelines for asymptomatic pregnant women who were possibly exposed to the Zika virus. Currently, women with possible exposure to the Zika virus are recommended to be tested using Zika virus Immunoglobulin M (IgM) ELISA. This test detects human antibodies or proteins that fight Zika infection. However, “emerging epidemiologic and laboratory data” have revealed that these antibodies may remain in the body for more than 12 weeks after infection in some cases, as with other flavivirus infections, especially those who are asymptomatic. Thus, antibody detection does not necessarily entail a recent infection.

While this information is relevant for all individuals who are exposed to the Zika virus, “it would have the greatest effect on clinical management of pregnant women with a history of living in or traveling to areas with Zika virus transmission,” according to the notice. In addition, the CDC notes infection during pregnancy may also elicit positive results using this test.

The CDC urges asymptomatic pregnant women who were potentially exposed to the Zika virus, either through travel or by residing in areas with active Zika transmission, receive “Zika virus nucleic acid test (NAT) testing at least once per trimester… in addition to IgM testing as previously recommended.”

Administering these two tests together may provide practitioners a more accurate means for “diagnosing recent Zika infection.” Nonetheless, a negative NAT test result does not mean an individual is not infected, since Zika RNA “declines over time.” To better determine if positive IgM results entail recent Zika infection, the CDC recommends “NAT testing of amniocentesis specimens or serial ultrasounds.” The CDC even suggests incorporating IgM into preconception counseling for those women who are not at “ongoing risk” for Zika virus infection, so as to set a baseline for results.

For women who begin to exhibit symptoms, or those whose sexual partners test positive for Zika, NAT testing is recommended. The CDC did not change testing guidelines for pregnant women who exhibit Zika-like symptoms.