CDC Releases Interim Guidance on Zika Testing and Interpretation of Results

Today, the Centers for Disease Control and Prevention (CDC) published interim guidance for Zika virus antibody testing and interpretation of results. Because of the differences in recommended clinical management of Zika and dengue virus infections, and the risk of adverse pregnancy outcomes in women infected with Zika virus during pregnancy, a conservative approach to the interpretation of antibody test results is necessary to reduce the possibility of a missed diagnosis of either infections. The timing of IgM antibody testing and the thresholds of plaque reduction neutralization test (PRNT) have changed.

• Serum IgM antibody test should be performed if real-time reverse transcription polymerase chain reaction (rRT-PCR) results are negative regardless of the day the specimen was collected.
• Based on earlier flavivirus research and limited preliminary data specific to Zika virus, the historical use of a 4-fold higher titer by PRNT might not discriminate between anti-Zika virus antibodies and cross-reacting antibodies in all persons who have been previously infected with or vaccinated against a related flavivirus (i.e., secondary flavivirus infection).
• Together with a positive or equivocal IgM to Zika or dengue virus:
o A PRNT titer >10 will be interpreted as a evidence of infection with that specific flavivirus infection when the PRNT to the other flavivirus(es) tested is <10.
o A PRNT titer <10 to a specific flavivirus will be interpreted as a no evidence of infection with  that virus.
o If PRNTs are positive i.e.,  >10 to multiple flaviviruses, this will be interpreted as evidence of recent infection with a flavivirus.
 
CDC will continue to update this guidance as these data are preliminary and as additional rRT-PCR data becomes available. For more information about this guidance, visit Interim Guidance for Interpretation of Zika Virus Antibody Test Results.