Testing & Diagnosis for Zika Virus

Testing for Zika virus infection is recommended for certain clinical scenarios. Read on to learn when testing is recommended, what tests to order, and potential testing challenges.

Assessing Need for Testing

All pregnant women in US states, the District of Columbia, and territories should be screened pdf icon[PDF – 372 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.

In addition, for symptomatic pregnant women with possible exposure, testing for dengue virus is also recommended because both viruses circulate in similar areas of the world and cause similar clinical presentations. Now that Zika is no longer newly introduced in the Americas, healthcare providers should ask patients about potential exposure to Zika before their current pregnancy to help guide decisions about testing and interpretation of test results.

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

When to test
If your patient… Testing recommendation
Was exposed to Zika AND has symptoms of Zika virus infection or a history or symptoms at any time during her pregnancy She should be tested for Zika and dengue as soon as possible.
  • Concurrent RNA nucleic acid amplification test (NAAT) testing and IgM testing for Zika and dengue viruses is recommended as soon as possible or through 12 weeks after symptom onset.
Lives in or frequently travels to an area with risk of Zika but does not have symptoms of Zika virus infection. She should be offered testing three times during pregnancy using RNA NAAT testing.
Traveled to or had sex without a condom with a partner who lived in or traveled to an area with risk of Zika but does not have symptoms of Zika virus infection Testing is not routinely recommended. Testing should be considered using a shared decision-making model that includes pretest counseling, individualized risk assessment, clinical judgment, patient preferences, and the jurisdiction’s recommendations.
  • Testing recommendations for this group of pregnant women may differ by jurisdiction. Please contact your state, tribal, local, or territorial health department for jurisdiction specific guidance.
Was exposed to Zika AND had birth defects potentially associated with Zika detected on a prenatal ultrasound Concurrent RNA NAT testing and Zika virus IgM testing is recommended. If amniocentesis is being done for clinical care, healthcare providers should also test the amniotic fluid for Zika virus RNA NAT. Testing of placental and fetal tissues may also be considered if results of maternal Zika virus testing are not definitive.
Testing Symptomatic Pregnant Women

Symptomatic pregnant women with possible Zika virus exposure should receive concurrent testing of serum and urine by NAAT and Zika virus IgM testing of serum as soon as possible, up to 12 weeks after symptom onset. In addition, for women with possible exposure to both Zika and dengue, testing of serum for dengue by NAAT and dengue virus IgM testing also should be performed.

  • A positive Zika virus NAAT result, in conjunction with a positive IgM result, should be interpreted as an acute maternal Zika virus infection.
  • A positive dengue virus NAAT result should be interpreted as an acute maternal dengue virus infection.
  • If Zika virus NAAT is positive on a single specimen but IgM antibody tests are negative, repeat NAAT on newly extracted RNA from the same specimen.
  • A positive Zika virus NAAT on either a serum or urine specimen in conjunction with a positive Zika IgM should be interpreted as confirmatory for acute Zika virus infection and repeat NAAT is not recommended.
  • A negative NAAT result in conjunction with a non-negative Zika virus IgM test result should be followed by plaque reduction neutralization test (PRNT).
Testing Asymptomatic Pregnant Women

Asymptomatic pregnant women with ongoing possible Zika virus exposure (i.e., residence in or frequent travel to an area with risk of Zika) should be offered RNA NAAT testing three times during pregnancy. Although there is no way to determine the timing of testing of asymptomatic pregnant women with only NAT testing, testing at the initiation of prenatal care with two additional tests performed during the course of the pregnancy, coinciding with prenatal visits should be considered. For this group, testing for Zika virus IgM antibodies is no longer routinely recommended because IgM antibodies can persist for months after infection; therefore, IgM results cannot reliably determine whether an infection occurred during the current pregnancy versus prior to conception.

Asymptomatic pregnant women with recent possible exposure to Zika but no ongoing exposure (i.e., travelers) may be considered for testing. Although not routinely recommended, testing may be considered on a case-by-case basis using a shared physician-patient decision-making model and in line with jurisdictional recommendations.

Note: Jurisdictions may take into account local epidemiologic considerations (e.g., seasonality, geography, and mosquito surveillance and control factors) in making recommendations for Zika virus testing for this group of pregnant women; therefore, testing recommendations for this group of pregnant women may differ by jurisdiction. Please contact your state, tribal, local, or territorial health department for jurisdiction-specific guidance.

Testing Pregnant or Postpartum Women with Possible Zika Virus Exposure Who Have a Fetus with Prenatal Ultrasound Findings or an Infant with Physical Exam Findings Consistent with Possible Zika Virus-Associated Birth Defects

For pregnant women exposed to Zika whose fetus has birth defects potentially associated with Zika detected on ultrasound or whose infant has physical exam findings consistent with possible Zika-virus associated birth defects, concurrent testing of serum and urine by RNA NAAT and Zika virus IgM testing of serum is recommended, following the algorithm for symptomatic pregnant women. If amniocentesis is performed as part of clinical care, healthcare providers should consider RNA NAAT testing of amniocentesis specimens and results should be interpreted within the context of the limitations of amniotic fluid testing. It is unknown how sensitive or specific RNA NAAT testing of amniotic fluid is for congenital Zika virus infection or what proportion of infants born after infection will have abnormalities.

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 webpage 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 research settings. 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 testing can also be performed on maternal whole blood, amniotic fluid, plasma, and urine. Other testing that can be performed includes Zika virus RT-PCR on formalin-fixed placental tissues; histopathologic examination and immunohistochemical staining may be performed in selected scenarios . 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 NAAT testing may not identify Zika virus RNA in a woman with Zika virus infection if the period of viremia has passed. IgM testing should 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 have been vaccinated against yellow fever or Japanese encephalitis.

New data suggest that, similar to some other flavivirus infections, Zika virus IgM antibodies may remain in the body for months after infection, making it difficult to use Zika virus IgM tests to determine if women might have been infected before or after they became pregnant. IgM tests are also susceptible to false positives and cross-reactivity with other flaviviruses, especially when an individual has been vaccinated against or previously infected with a related flavivirus. In addition, as the prevalence of Zika virus disease declines, the lower prevalence increases the probability that positive test results are false positives. This new information is particularly relevant for pregnant women who live in or frequently travel to areas with risk of Zika.

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 consultation service for health officials and healthcare providers caring for pregnant women. To contact the service, call 800-CDC-INFO or send inquiries to CDC-INFO via the online form.

Clinician Resources
Updated Interim Pregnancy Guidance: Testing and interpretation recommendations for a pregnant woman with possible exposure to Zika virus

Zika Testing for Symptomatic Pregnant Women with Possible Zika Exposure


Zika Testing for Asymptomatic Pregnant Women with Possible Zika Exposure


Zika Test Result Interpretation Table


Zika Pregnancy Screening Tool