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.

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.

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.

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 Zika virus 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 Zika virus testing is not routinely recommended. Zika virus 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.
  • Zika virus 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 Zika virus RNA NAT testing and 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 Guidance for Symptomatic Pregnant Women

For pregnant women with a clinically compatible illness and recent possible exposure to dengue and Zika virus with a specimen collected within 12 weeks of symptom onset:

  • Specimens should be collected as soon as possible after onset.
  • The following diagnostic testing should be performed at the same time:
    • Dengue and Zika virus NAAT and IgM antibody testing on a serum specimen, and
    • Zika virus NAAT on a urine specimen.
  • A positive NAAT result on any specimen typically provides adequate evidence of recent infection. However, if NAAT is only positive for Zika virus on a single specimen and IgM antibody testing is negative, the NAAT should be repeated on newly extracted RNA from the same specimen to rule out false-positive NAAT results.
  • If both dengue and Zika virus NAATs are negative but either IgM antibody test is positive, confirmatory PRNTs should be performed against dengue, Zika, and other flaviviruses endemic to the region where exposure occurred.
  • The interpretation for IgM and neutralizing antibody test results in a symptomatic pregnant woman is similar to that for non-pregnant patients; however, because dengue and Zika virus IgM antibodies can be detected in serum for months after an infection, the specific timing of infection cannot be determined, and other factors (e.g., epidemiologic and clinical findings) should be used to assess the likelihood that the current illness was due to either dengue or Zika virus and that exposure occurred during the pregnancy.

See the testing algorithm and test interpretations for symptomatic pregnant women [PDF – 2 pages].

Healthcare providers are strongly encouraged to read the full testing guidance: Dengue and Zika virus diagnostic testing for patients with a clinically compatible illness and risk for infection with both viruses

Testing Guidance for Asymptomatic Pregnant Women

For asymptomatic pregnant women with ongoing possible Zika virus exposure (i.e., residence in or frequent travel to an area with risk of Zika):

  • Zika virus NAAT testing is recommended three times during pregnancy.
  • Zika virus IgM antibody testing is no lon­ger routinely recommended because IgM can persist for months after infection; therefore, IgM results cannot reliably determine whether an infection occurred during the current pregnancy.
  • Recommendations for the timing of Zika virus NAAT testing are at the initial prenatal care visit, followed by two additional Zika virus NAAT tests performed during pregnancy, coinciding with non-consecutive prenatal visits. Zika virus testing is not recommended for pregnant women with a previous diagnosis of laboratory-confirmed Zika virus infection.
  • Dengue virus testing is not recommended for individuals without a clinically compatible illness.

For asymptomatic pregnant women with recent possible exposure to Zika virus but no ongoing exposure (i.e., through travel or sexual exposure):

  • Zika virus testing may be considered.
    • Although not routinely recommended, testing may be considered on a case-by-case basis and in line with jurisdictional recommendations.
    • If Zika virus testing is conducted, follow algorithm for symptomatic pregnant women using timeframe from last possible exposure.
  • Dengue virus testing is not recommended for individuals without a clinically compatible illness.
  • 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 asymptomatic pregnant women with possible recent exposure to Zika virus but no ongoing exposure; 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.

See the testing algorithm and test interpretations for asymptomatic pregnant women. [PDF – 2 pages]

Pregnant women with possible exposure to Zika virus and who have a fetus with prenatal ultrasound findings consistent with congenital Zika virus infection 

  • Zika virus NAAT and IgM testing should be performed on maternal serum and NAAT on maternal urine.
  • If amniocentesis is being performed as part of clinical care, Zika virus NAAT testing of amniocentesis specimens should also be performed and results 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 of placental and fetal tissues may also be considered (see guidance for Collecting and Submitting Specimens at Time of Birth for Zika virus Testing).

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 maternal serum and urine by RNA NAAT and Zika virus IgM testing of serum is recommended. If amniocentesis is performed as part of clinical care, healthcare providers should consider Zika virus 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 of placental and fetal tissues may also be considered.

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