The US Centers for Disease Control and Prevention (CDC) today updated its Zika antibody testing guidance for women who live in or travel to affected areas, based on the latest evidence that Zika virus immunoglobulin M (IgM) antibodies can persist beyond 12 weeks in some infected patients.
Prolonged viral IgM persistence has been seen with other flaviviruses, such as dengue and West Nile virus.
Positive result could be deceptive
In a Health Alert Network (HAN) notice to clinicians, the CDC said a positive IgM test may not always indicate a recent infection and that the greatest clinical implications are for managing the care of pregnant women who have lived in or traveled to areas where Zika is spreading locally.
Pregnant women who test positive on Zika IgM tests may have been infected with the virus and developed an antibody either before or after conception.
The CDC recommends that pregnant women be screened for risk of Zika exposure and symptoms of the disease. It said asymptomatic pregnant women who have a history of living in or traveling to Zika-affected areas should undergo the Zika nucleic acid test (NAT) at least once per trimester, alongside previously recommended IgM testing.
The agency added that a positive NAT test may provide a more definitive diagnosis of recent Zika infection. However, it included that caveat that a negative NAT test doesn't rule out recent infection, because viral RNA declines over time.
Other methods such as NAT of amniocentesis specimens if collected for other reasons or serial ultrasounds may provide more information to gauge if IgM test results indicate recent infection, the CDD said. It recommended that clinicians counsel all pregnant women in each trimester about the limitations of testing.
In a press release today, Henry Walke, MD, incident manager for the CDC's Zika response, said, "Our guidance today is part of our continued effort to share data for public health action as quickly as possible. As we learn more about the limitations of antibody testing, we continue to update our guidance to ensure that healthcare professionals have the latest information for counseling patients who are infected with Zika during pregnancy."
Zika-related pregnancy loss
In other developments, the CDC said one more pregnancy loss linked to Zika has been reported in the United States, raising the total to eight.
The number of babies born with Zika-related birth defects remained at 58, according to the latest information from the US Zika pregnancy registry. So far 1,409 women in the system have completed pregnancies with or without birth defects.
See also:
May 5 CDC HAN notice
May 5 CDC news release
May 4 CDC update
