New data on persistence of Zika virus in some infected individuals has led The Centers for Disease Control and Prevention (CDC) to issue an update on testing of asymptomatic pregnant women. The health advisory builds on interim guidance for health care providers that was published by CDC in July 2016.
Emerging epidemiologic and laboratory data, said CDC, indicate that Zika virus IgM can persist beyond 12 weeks in a subset of infected people. As a result, IgM detection may not always indicate a recent infection. A Puerto Rican study of symptomatic patients with nucleic acid test (NAT)-confirmed Zika shows persistence of the virus IgM in 100% of participants at 8 to 15 days after symptom onset and in 87% at more than 60 days after symptom onset. Median time to first negative Zika virus IgM was 4 months (range 8-210 days) according to unpublished data from the ongoing study.
CDC noted that while IgM persistence could affect test interpretation in all patients infected with Zika, 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 before conception. Pregnant women who test positive for IgM antibody may have been infected with the virus and developed the response before conception.
CDC’s recommendations for testing symptomatic pregnant women are unchanged. For asymptomatic pregnancy women who live in or frequently travel to areas with Zika virus transmission with CDC Zika Travel Notices, the agency recommends:
· Screening for risk of Zika exposure and symptoms, with prompt NAT testing if symptoms develop during pregnancy or a sexual partner tests positive for Zika;
· Consideration of NAT testing at least once per trimester, unless a previous test has been positive;
· Consideration of NAT testing of amniocentesis specimens if the test is performed for other reasons;
· Patient counseling each trimester on limitations of IgM and NAT testing; and
· Consideration of IgM testing to determine baseline Zika virus IgM levels as part of preconception counseling.