The Centers for Disease Control and Prevention (CDC) has responded to the declining prevalence of Zika virus in the Americas, as well as emerging evidence "indicating prolonged detection of Zika immunglobulin M (IgM) antibodies,” by updating its interim guidance for US healthcare providers who are treating pregnant women with possible Zika virus exposure.
The authors of the guidance note that as prevalence of the disease continues to decline, the likelihood of false-positive test results is conversely increasing. This may be because recent evidence suggests that Zika virus IgM antibodies can persist in the body for > 12 weeks after infection. As such, the authors note that “IgM test results cannot always reliably distinguish between an infection that occurred during the current pregnancy and one that occurred before the current pregnancy, particularly for women who had potential exposure to the virus previous to their current pregnancy.” Healthcare providers should mention the limitations to current testing methods when counseling pregnant women on the risks and benefits involved in testing for the virus during their pregnancy.
Ultimately, the new guidance stresses the use of a “shared decision-making model” for testing and screening pregnant women. In this model, patients work closely with healthcare providers to make important decisions regarding testing and care. These decisions are informed by “patient preferences and values, clinical judgment, and a balanced assessment of risks and expected outcomes.”
According to the guidance, some of the key updated recommendations include:
- Having healthcare providers ask all pregnant women in the United States and US territories about potential exposure to Zika virus both before and during current pregnancies; this should happen at each prenatal care visit.
- Pregnant women who report potential Zika virus exposure or present with associated symptoms should be tested to diagnose the cause of their symptoms. The updated recommendation calls for a concurrent Zika virus nucleic acid test (NAT) and serologic testing "as soon as possible through 12 weeks after symptom onset."
- Healthcare providers should offer Zika virus NAT testing a total of 3 times during pregnancy to symptomatic pregnant women who have ongoing potential exposure to the virus. The authors note that IgM testing is no longer a routine recommendation because IgM is capable of persisting for months after infection. As such, the test cannot reliably answer the question of whether the infection occurred during pregnancy or not. Furthermore, the authors write that pregnant women who are given a diagnosis of laboratory-confirmed Zika virus any time during their pregnancies, are not recommended to receive any additional testing. However, they do say that pregnant women without laboratory-confirmed diagnosis should be offered NAT testing as soon as they start prenatal care. If healthcare providers do not detect Zika virus RNA, “2 additional [NAT] tests should be offered [to these women] during the course of pregnancy coinciding with prenatal visits.”
- Pregnant women who are asymptomatic and have had potential exposure to the virus, but do not have ongoing exposure, are not recommended to be tested for Zika virus. However, the decision to test should be based on the "shared patient-provider decision-making model." Furthermore, certain jurisdictions might recommend that these women undergo testing based on “the epidemiology of Zika virus and other epidemiologic considerations.” The authors also noted that as the prevalence of the disease declines, “the updated recommendations for the evaluation and testing of pregnant women with recent possible Zika virus exposure but without ongoing exposure are now the same for all areas with any risk for Zika virus transmission.”
- Pregnant women who report having been potentially exposed to Zika virus, who have a fetus with prenatal ultrasound findings that suggest congenital Zika virus syndrome, are recommended to receive both tests (NAT and IgM) “to assist in establishing the etiology of the birth defects.”
- For certain scenarios, authors note that testing placental and fetal tissue specimens can be used for diagnostic purposes—such as for women who do not have a laboratory-confirmed diagnosis of Zika, but have an infant who may have potential associated birth defects. However, they point out that this is not a routine recommendation for pregnant women who are asymptomatic, have potentially been exposed to the virus (but do not have ongoing potential exposure), and have an infant who was born without evidence of potential associated birth defects.
- Due to the fact that Zika virus IgM is no longer recommended for asymptomatic pregnant women who have ongoing potential exposure to the virus, Zika virus IgM “as part of preconception counseling to establish baseline IgM results for nonpregnant women with ongoing possible Zika virus exposure is not warranted.”
As the CDC reviews emerging evidence, they will continue to update their recommendations to incorporate what is learned. In the meantime, the CDC stresses that pregnant women should avoid any areas that put them and their child at risk for Zika virus infection. Furthermore, pregnant women should also be receiving counseling on preventive measures that can be taken to protect themselves and their child against the virus.