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Zika Virus Testing for Infants and Children

Congenital Zika Virus Infection

When should an infant with possible congenital infection be tested for Zika virus?

Testing is recommended for infants born to mothers with laboratory evidence of Zika virus infection during pregnancy, and for infants who have abnormal clinical findings suggestive of congenital Zika virus syndrome and a maternal epidemiologic link suggesting possible transmission, regardless of maternal Zika virus test results.

For infants born to mothers with risk factors for maternal Zika virus infection (travel to or residence in an area of active Zika virus transmission or sex without a condom or other barrier protection with a partner with travel to or residence in such an area) for whom maternal testing was not performed before delivery, assessment of the infant, including comprehensive physical exam and careful measurement of head circumference should be performed. Maternal diagnostic testing should be performed and testing of the placenta for Zika virus PCR should be considered. If an infant appears clinically well, further evaluation and infant testing can be deferred until maternal test results are available. However, if there is concern about infant follow-up, infant testing should be performed before hospital discharge.

In many cases, infant testing results will not be available before hospital discharge. If test results are not available before hospital discharge, infants should be presumed to have congenital Zika virus infection until test results are available. Infants with confirmed and probable Zika virus infection should be managed in the same way, according to guidance.

For all scenarios, guidelines will be updated as additional information becomes available. Healthcare providers should contact their local, state, or territorial health departments to arrange testing.

How are infants diagnosed with possible congenital Zika virus infection?

Zika virus infection can be diagnosed by real-time reverse transcription-polymerase chain reaction (rRT-PCR) or through serologic testing. It has not been established which test is most reliable for a diagnosis of congenital infection in newborns. Therefore, both should both be performed. A Zika virus rRT-PCR test should be performed on both infant serum and urine, and Zika virus immunoglobulin M (IgM) antibody enzyme-linked immunosorbent assay (ELISA) should be performed on infant serum. Testing should be performed on infant specimens; testing of cord blood is no longer recommended. If cerebrospinal fluid (CSF) is obtained for other studies, rRT-PCR testing for Zika virus RNA and Zika virus IgM should be performed on CSF. Infant testing for Zika virus should be performed within the first 2 days after birth, particularly in areas where Zika virus is currently circulating because if testing is performed later, distinguishing between perinatally or postnatally acquired infections from congenital infection will be difficult. 

A Zika rRT-PCR positive result in an infant sample confirms the diagnosis of congenital Zika virus infection. Zika virus IgM detected in an infant, with a negative rRT-PCR result, should be interpreted as probable congenital Zika virus infection. If both Zika virus rRT-PCR and Zika virus IgM results are negative, the infant is considered to be negative for congenital Zika virus infection, but infant test results should be interpreted in the context of timing of infection during pregnancy, maternal serology, clinical findings consistent with Zika virus disease in infants, and additional confirmatory testing (plaque reduction neutralization testing [PRNT]).

If the infant’s initial sample is IgM positive, but PRNT was not performed on the mother’s sample, PRNT should be performed on the infant’s initial sample. However, PRNT cannot distinguish between maternal or infant antibodies. Maternal antibodies in the infant are expected to wane by 18 months. To confirm a congenital infection, PRNTs should be performed on a sample collected from an infant aged 18 months whose initial sample is IgM positive and neutralizing antibodies were detected by PRNT in either the infant’s or mother’s sample. If the infant’s initial sample is negative by both IgM ELISA and rRT-PCR but clinical concerns remain (e.g., microcephaly with negative evaluation for other known causes), PRNT at 18 months can be considered. If PRNT results at 18 months are negative, the infant is considered not to have congenital Zika virus infection. If PRNT results are positive, congenital Zika infection is presumed, but postnatal infection cannot be excluded, especially among infants living in an area with active Zika virus transmission. 

Infant test results*  
rRT-PCR IgM Interpretation
Positive Positive or Negative Confirmed congenital Zika virus infection
Negative Positive Probable congenital Zika virus infection+
Negative Negative Negative for congenital Zika virus infection+

When should infants be tested for congenital Zika virus infection?

Infant testing for congenital Zika virus infection should be performed within the first 2 days after birth, particularly in areas where Zika virus is currently circulating. If testing is performed later, distinguishing between perinatally or postnatally acquired infections from congenital Zika infection will be difficult.

Postnatal Zika Virus Infection

When should an infant or a child be tested for postnatal Zika virus disease?

Criteria for testing will vary by state. However, postnatal Zika virus disease should be suspected in an infant or child aged <18 years who 1) traveled to or resided in an area with ongoing transmission of Zika virus within the past 2 weeks or, for an adolescent, who might have been exposed to Zika virus through sexual contact with a partner who traveled to or resided in an area of active Zika virus transmission, and 2) has ≥2 of the following manifestations: fever, rash, conjunctivitis, or arthralgia. Because transmission of Zika virus from mother to infant during delivery is possible, postnatal Zika virus disease should also be suspected in an infant during the first 2 weeks of life 1) whose mother, within approximately 2 weeks of delivery, was potentially exposed to Zika virus through travel to or residence in an area of active Zika virus transmission or through sexual transmission, and 2) who has ≥2 of the following manifestations: fever, rash, conjunctivitis, or arthralgia. Healthcare providers should contact their local, state or territorial health departments to arrange testing. Zika virus disease is a nationally notifiable condition.

Arthralgia is a known symptom of Zika virus disease. How might arthralgia manifest in young children?

Arthralgia can be difficult to detect in infants and young children and can manifest as irritability, walking with a limp (for ambulatory children), difficulty moving or refusing to move an extremity, pain on palpation, or pain with active or passive movement of the affected joint.

How is possible postnatal Zika virus infection confirmed in infants and children?

During the first two weeks after the start of illness, Zika virus disease can often be diagnosed by performing real-time reverse transcriptase polymerase chain reaction (rRT-PCR) on serum and urine. Zika virus rRT-PCR should be performed on serum and urine collected <14 days after onset of symptoms in patients with suspected Zika virus disease.  A positive Zika virus rRT-PCR confirms Zika virus infection.  However, because Zika virus RNA in serum and urine decreases over time, a negative rRT-PCR does not rule out Zika virus infection; in this case, serologic testing should be performed. If Zika virus rRT-PCR results are negative for both specimens, serum should be tested by antibody detection methods.

Serology assays can also be used to detect Zika virus-specific IgM and neutralizing antibodies, which typically develop toward the end of the first week of illness.  A positive IgM result does not always indicate Zika virus infection and can be difficult to interpret because cross-reactivity with related flaviviruses (e.g., dengue, Japanese encephalitis, West Nile, yellow fever) can occur. A positive Zika virus IgM result may reflect previous vaccination against a flavivirus; previous infection with a related flavivirus; or current infection with a flavivirus, including Zika virus.

Plaque-reduction neutralization testing (PRNT) can be performed to measure virus-specific neutralizing antibodies to confirm primary flavivirus infections and differentiate from other viral illnesses. PRNT can be performed to measure virus-specific neutralizing antibodies to Zika virus, but neutralizing antibodies may still yield cross-reactive results in a person who was previously infected with another flavivirus, such as dengue, or has been vaccinated against yellow fever or Japanese encephalitis.

If Zika virus testing of an infant or a child is indicated, how is the test ordered?

Zika virus testing is performed at many state and territorial health departments, and at CDC. Healthcare providers should contact their local, state or territorial health department to facilitate testing. See the Diagnostic Testing webpage for information on how to obtain Zika testing.

What are the challenges in interpreting Zika virus testing in an infant or child?

Zika virus testing in infants and children has several challenges. RT-PCR tests may not detect Zika virus RNA in an infant who had Zika virus infection in utero or a child if the period of viremia has passed. Serologic tests for Zika virus can be falsely positive because of cross-reacting antibodies against related flaviviruses (e.g., dengue and yellow fever viruses). Plaque-reduction neutralization testing (PRNT) can be performed to measure virus-specific neutralizing antibodies to Zika virus, but neutralizing antibodies may still yield cross-reactive results in infants due to maternal antibodies that were transferred to the infant. It is important to work closely with local, state or territorial health departments to ensure the appropriate test is ordered and interpreted correctly.

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