New CDC Guidance on Zika Testing Released

On May 31, 2016, the Centers for Disease Control and Prevention (CDC) updated its interim guidance on screening for, and diagnosis of, Zika virus.

The move comes as the virus, which is transmitted via the Aedes aegypti mosquito and has been linked with complications for pregnant women, continues to spread in South America and the Caribbean, and new research has highlighted the potential for localized transmission during the summer months in the southern United States. Although the symptoms of Zika are relatively mild, the virus has been shown to cause microcephaly in the newborns of pregnant women who have been infected, leading to an international debate regarding the safety of travel to regions where it is prevalent.

Indeed, the crisis may impact athlete and spectator participation during the Olympic Games this summer, which are scheduled to be held in Rio de Janeiro. Brazil has been viewed as “ground zero” for Zika since 2014.

In its updated guidance, published in the Morbidity and Mortality Weekly Report for May 31, the CDC notes that the US Food and Drug Administration has issued an Emergency Use Authorization for the Zika IgM Antibody Capture Enzyme-Linked Immunosorbent Assay (Zika MAC-ELISA), which is already being used in “qualified public health and Department of Defense laboratories” across the country. According to the CDC, the Zika MAC-ELISA is used for “the qualitative detection of Zika virus IgM antibodies in serum or cerebrospinal fluid collected from persons meeting the clinical and epidemiologic criteria for suspected Zika virus disease.” The CDC recommends that findings from Zika MAC-ELISA be confirmed via plaque reduction neutralization testing (PRNT) to “resolve false-positive results that might be caused by cross-reactivity or nonspecific reactivity.”

In general, the CDC emphasizes that antibody testing isn’t required in cases in which Zika virus disease is suspected and confirmed via positive rRT-PCR. However, those with a suspected Zika infection found to be negative on rRT-PCR should be evaluated with serum IgM antibody testing “because of the decline in the level of viremia over time and possible inaccuracy in reporting of dates of illness onset.”

Given the concerns regarding Zika and pregnancy, the CDC also highlights specific approaches for asymptomatic pregnant women living in areas with local Zika virus transmission. It suggests that IgM testing be performed upon initiation of prenatal care (during the second trimester) and/or if fetal abnormalities are detected during ultrasound. In asymptomatic pregnant women who have traveled to areas where Zika virus transmission has been reported, antibody testing should be performed on specimens collected two to 12 weeks, post-travel.

Regarding the management of cases of suspected Zika infection, the CDC guidance stipulates that symptomatic and asymptomatic pregnant women “with serologic or molecular evidence of recent Zika virus infection should be evaluated and managed for possible adverse pregnancy outcomes and reported to the US Zika Pregnancy Registry or the Puerto Rico Zika Active Pregnancy Surveillance System.” In cases in which diagnostic tests designed to differentiate between Zika and Dengue (which has similar initial symptoms) are inconclusive, the CDC recommends that patients be “clinically managed for both infections because they might have been infected with either virus.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.