As a result of increasing knowledge about the Zika virus, the CDC updated their recommendations. The changes are based on declining trends in the number of reported cases of Zika virus infection in the Americas, emerging evidence on prolonged detection of Zika IgM antibodies, and new limitations for interpreting serologic tests during pregnancy. IgM is most likely to be detected in the first 12 weeks after infection but may persist beyond 12 weeks in some infected individuals, limiting the ability of testing to determine whether an infection occurred during or prior to pregnancy. False positive results and cross-reactivity with other flaviviruses can occur with IgM assays. Therefore, it is important to ascertain whether a woman had exposure to flaviviruses other than Zika virus before the current pregnancy because a positive IgM result might have been caused by cross-reactivity from a previous flavivirus exposure. Given the possibility of a false positive result, laboratory test results should not be released until all testing is complete.
Zika virus tests should be performed in:
- Symptomatic pregnant women with possible exposure to Zika virus
- Asymptomatic pregnant women with ongoing possible exposure to Zika virus
- Pregnant women with possible exposure to Zika virus who have a fetus with prenatal ultrasound findings consistent with congenital Zika virus infection
- Non-pregnant symptomatic individuals with possible exposure to areas with risk of Zika virus transmission
Zika virus testing may be considered for:
- Asymptomatic pregnant women with recent possible but no ongoing exposure to Zika virus (i.e., travelers). Although not routinely recommended, testing may be considered on a case-by-case basis and in line with jurisdictional recommendations.
Zika virus testing is not recommended for:
- Non-pregnant asymptomatic individuals
- Pre-conception screening
The primary specimens for Zika virus testing should be paired serum and urine samples. Some emergency authorization tests may require other samples types. However, serum should always be obtained in case nucleic acid testing (NAT) testing is indicated after initial test results. NAT (on serum and urine) and IgM serological testing should be performed concurrently when testing symptomatic pregnant women. Specific guidance for laboratories is given by the CDC.