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Testing & Diagnosis


Assessing Need for Testing

All pregnant women in US states, the District of Columbia, and territories should be screened [PDF – 250 KB] for possible Zika virus exposure and symptoms at each prenatal care visit. Possible exposure to Zika virus that might warrant testing includes:

  • Recent travel to or residence in an area with risk of Zika (during pregnancy or the periconceptional period [the 6 weeks before last menstrual period or 8 weeks before conception]), or
  • Sex (vaginal, anal, or oral sex) or sharing sex toys without a condom during pregnancy with a person who traveled to or lives in an area with risk of Zika.

Testing for Zika Virus

Zika virus testing is performed at CDC, at several state, local, and territorial health departments, and at some commercial laboratories. Several tests are available to help determine if a person is infected with Zika virus. Healthcare providers should contact their state or local health department to facilitate testing. See the Testing for Zika Virus webpage for information on how to submit specimens for Zika testing.

Laboratory evidence of a confirmed recent Zika virus infection includes

  1. Detection of Zika virus or Zika virus RNA or antigen in any body fluid or tissue specimen; or
  2. Positive or equivocal Zika virus or dengue virus IgM test on serum with a positive titer for Zika virus (≥10) from plaque reduction neutralization testing (PRNT) together with negative PRNT titer (i.e., <10) for dengue virus. Interpretation of serologic results has been described and published in an MMWR article.

When to Test

If your patient… Testing recommendation
Lives in or frequently travels to an area with risk of Zika virus infection that has a CDC Zika travel notice Pregnant women who live in or frequently travel to an area with a CDC Zika travel notice are at risk of getting Zika throughout pregnancy. For this reason, testing is recommended regardless of whether the patient has symptoms of infection.
  • Zika virus IgM testing in both the first and second trimesters
  • Consider RNA nucleic acid test (NAT) testing at least once per trimester, (unless a previous test has been Zika virus positive)

If a pregnant woman has symptoms of Zika at any time during her pregnancy, she should be tested for Zika even if she has already been tested during the current trimester.

Traveled to or had sex without a condom with a partner who lived in or traveled to an area with a CDC Zika travel notice, with or without symptoms of infection These pregnant women should be tested for Zika after the exposure regardless of whether or not the patient has experienced symptoms.
Traveled to or had sex without a condom with a partner who lived in or traveled to an area with risk of Zika virus infection but no CDC Zika travel notice and has symptoms of possible Zika virus infection or a fetal ultrasound that indicates abnormalities that might be related to Zika These pregnant women should be tested if they develop symptoms of Zika or if their fetus has abnormalities on an ultrasound that may be related to Zika infection.
Traveled to or had sex with a partner who lived in or traveled to an area with risk of Zika virus infection but no CDC Zika travel notice and does not have symptoms of possible Zika virus infection and no fetal ultrasound that indicates abnormalities that might be related to Zika Because the level of risk of Zika virus infection is unknown in areas with Zika risk but without CDC Zika travel notices, routine testing is not recommended for pregnant women who have exposure to those areas but who do not have symptoms. However, testing may be offered on a case-by-case basis.

Testing Symptomatic Pregnant Women

Pregnant women who report signs or symptoms consistent with Zika virus disease (acute onset of fever, rash, headache, arthralgia, conjunctivitis, muscle pain) should be tested for Zika virus infection. The testing recommendations for symptomatic pregnant women are the same regardless of the circumstances of possible exposure.

The type of testing recommended varies depending on the time of evaluation relative to symptom onset or possible exposure. For symptomatic pregnant women who traveled to or had sex without a condom with a partner who lived in or traveled to an area with risk of Zika and who seek care:

<2 weeks after symptom onset: testing of serum and urine by RNA nucleic acid testing (NAT; e.g. rt-PCR). A positive RNA NAT result confirms the diagnosis of recent maternal Zika virus infection. Symptomatic pregnant women with negative RNA NAT results should receive both Zika virus IgM and dengue virus IgM testing. If Zika virus RNA NAT testing is requested from laboratories that do not have IgM testing capacity or a process to forward specimens to another testing laboratory, storing of additional serum samples is recommended for IgM testing in the event of a negative RNA NAT result. If either the Zika virus or dengue virus IgM test yields positive or equivocal results, PRNT should be performed on the same IgM-tested sample or a subsequently collected sample to rule out false-positive results. Interpretation of serologic results has been described and published in an MMWR.

2–12 weeks after symptom onset: Zika virus and dengue virus IgM testing of serum is recommended. If the Zika virus IgM testing yields positive or equivocal results, reflex RNA NAT testing should be automatically performed on the same serum sample to determine whether Zika virus RNA is present. A positive RNA NAT result confirms the diagnosis of recent maternal Zika virus infection. However, if the RNA NAT result is negative, a positive or equivocal Zika virus IgM test result should be followed by PRNT. Positive or equivocal dengue IgM test results with a negative Zika virus IgM test result should also be confirmed by PRNT. Interpretation of serologic results has been described and published in a MMWR.

Testing Asymptomatic Pregnant Women

Testing recommendations for asymptomatic pregnant women with possible Zika virus exposure differ based on the circumstances of possible exposure (i.e., ongoing versus limited exposure), the area of possible exposure, and the elapsed interval since the last possible Zika virus exposure.

Asymptomatic pregnant women who traveled to or had sex without a condom with a partner who lived in or traveled to an area with a CDC Zika travel notice who are evaluated <2 weeks after possible Zika virus exposure should be offered serum and urine RNA NAT testing. A positive RNA NAT result confirms the diagnosis of recent maternal Zika virus infection. However, because viral RNA in serum and urine declines over time and depends on multiple factors, asymptomatic pregnant women with a negative RNA NAT result require additional testing to exclude infection. These women should return 2–12 weeks after possible Zika virus exposure for Zika virus IgM testing. A positive or equivocal IgM test result should be confirmed by PRNT.

Asymptomatic pregnant women who traveled to or had sex without a condom with a partner who lived in or traveled to an area with a CDC Zika travel notice, who seek care 2–12 weeks after possible Zika virus exposure should be offered Zika virus IgM testing. If the Zika virus IgM test yields positive or equivocal results, reflex RNA NAT testing should be performed on the same sample. If the RNA NAT result is negative, PRNT should be performed.

Asymptomatic pregnant women who traveled to or had sex without a condom with a partner who lived in or traveled to an area with Zika risk but no CDC Zika travel notice: Testing for this group is not routinely recommended. Positive results are more likely to be false when there are lower levels of Zika virus transmission or co-circulation of other flaviviruses. Positive Zika virus serology results require additional confirmatory testing and these results may take several weeks. Healthcare providers can offer testing on a case-by-case basis for asymptomatic pregnant women who are concerned about Zika virus infection. However, pretest counseling should clearly convey the limitations associated with interpretation of test results.

Asymptomatic pregnant women who have an ongoing risk for Zika virus exposure (i.e., residence in or frequent travel to an area with risk of Zika) should receive IgM testing as part of routine obstetric care during the first and second trimesters. In addition, given new information about the possibility of prolonged Zika IgM, consider RNA NAT testing at least once per trimester. RNA NAT testing can occur concurrently with IgM testing in the 1st and 2nd trimester.

If there is a positive or equivocal IgM test result without concurrent RNA NAT testing, RNA NAT testing is recommended. RNA NAT testing provides the potential for a definitive diagnosis of Zika virus infection. Negative RNA NAT results after a positive or equivocal Zika virus IgM test result should be followed by PRNT.

Healthcare providers should consider RNA NAT testing of amniocentesis specimens if amniocentesis is performed for other reasons and results should be interpreted within the context of the limitations of amniotic fluid testing. It is unknown how sensitive or specific RNA NAT testing of amniotic fluid is for congenital Zika virus infection or what proportion of infants born after infection will have abnormalities.

Providers should continue to screen pregnant women for risk of Zika exposure and symptoms of Zika and promptly test pregnant women using RNA NAT if they develop symptoms at any point during pregnancy or if their sexual partner tests positive for Zika.

Healthcare providers should counsel pregnant women about the limitations of Zika testing. A positive Zika virus IgM test result can have multiple interpretations: a recent Zika infection; a recent infection with a similar type of virus, such as dengue; a false positive result; or a past infection with Zika virus.

Testing Partners of Pregnant Women

CDC recommends Zika virus testing for anyone who is not pregnant who has been exposed to Zika and who also has Zika symptoms, including sex partners of pregnant women. See CDC’s laboratory guidance for testing recommendations for non-pregnant people.

Testing does not determine how likely a person is to pass Zika virus through sex. Because Zika virus can remain in some fluids (e.g., semen) longer than blood, someone might have a negative blood test, but still carry Zika in their genital secretions.

Further, intermittent shedding in semen can occur with other viruses and the pattern of Zika virus shedding in semen is unknown. In addition, the detection of Zika virus RNA in semen might not indicate the presence of infectious virus in semen. Testing semen and vaginal fluids for Zika virus is not currently available outside of the research setting. Studies are underway to better understand the performance of these tests, the persistence of Zika virus in these fluids, and how best to interpret the results.

Testing Information

For more information on diagnostic testing for Zika, see Testing for Zika.

Specimens

Zika virus RNA NAT and serology assays can be performed on maternal serum. Zika virus RNA NAT can also be performed on maternal whole blood, amniotic fluid, plasma, and urine. Other testing that can be performed includes the following: 1) histopathologic examination and immunohistochemical staining of the placenta and umbilical cord, and 2) Zika virus testing of frozen placental tissue and cord tissue. For a number of reasons, the use of cord blood to diagnose Zika virus infection is not recommended. It is important to work closely with your state or local health department to ensure the appropriate test is ordered and interpreted correctly.

Testing Challenges

RNA NAT testing may not demonstrate Zika virus RNA in a woman with Zika virus infection if the period of viremia has passed. IgM testing can be performed, however, cross-reactivity with related flaviviruses (e.g., dengue and yellow fever viruses) is common. PRNT can be performed to measure virus-specific neutralizing antibodies to Zika virus, but neutralizing antibodies may still yield cross-reactive results in persons who were previously infected with another flavivirus, such as dengue, or has been vaccinated against yellow fever or Japanese encephalitis.

In addition, some areas with a CDC Zika travel notice are moving into a second season in which local mosquitoes may be spreading Zika. New data suggest that, similar to some other flavivirus infections, Zika virus antibodies may remain in the body for months after infection, making it difficult to use Zika virus IgM tests to determine whether women might have been infected before or after they became pregnant. This new information is particularly relevant for pregnant women without symptoms who live in or frequently travel to areas with a CDC Zika travel notice.

Ordering Tests

Each clinical scenario is unique, and healthcare providers should consider all available information when ordering a test for Zika virus infection, including patient travel history or possible exposure through sexual contact, history of flavivirus infection, vaccination history, ultrasound findings, and the presence of symptoms.

All laboratory testing requests and results reports for pregnant women should clearly indicate pregnancy status. This will facilitate prioritization of testing, ascertainment of pregnancies affected by Zika, and consistent interpretation of laboratory results.

Healthcare providers should work closely with the state, local, or territorial health department to ensure that the appropriate test is ordered and interpreted correctly. In addition, CDC maintains a 24/7 Zika consultation service for health officials and healthcare providers caring for pregnant women. To contact the service, call 770-488-7100 and ask for the Zika Pregnancy Hotline or email ZIKAMCH@cdc.gov.

Clinician Resources

Updated Interim Pregnancy Guidance

Zika Pregnancy Testing Algorithm


Zika Pregnancy Screening Tool

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