Interpretation of results of laboratory testing in infants with suspected congenital Zika virus infection

rRT-PCR: real-time reverse transcription-polymerase chain reaction; IgM: immunoglobulin M; PRNT: plaque reduction neutralization test; CSF: cerebrospinal fluid.
* Laboratory testing for Zika virus infection in the infant includes serum and urine Zika virus rRT-PCR and serum Zika virus IgM. If IgM is positive, PRNT is used to exclude a false-positive result. In addition, if CSF is available, it should be tested for Zika virus with rRT-PCR and IgM. The initial samples should be collected from the infant within the first few days after birth if possible to distinguish between congenital, perinatal, and postnatal infection.
¶ Laboratory results should be interpreted in the context of timing of infection during pregnancy, maternal serology results, clinical findings consistent with congenital Zika syndrome, and any confirmatory testing with PRNT.
Δ Congenital Zika virus infection is confirmed if testing was performed within the first few days after birth. If testing was delayed and the infant lives in an area where there is ongoing transmission of Zika virus, a positive rRT-PCR does not distinguish between congenital and postnatal infection. However, if there was confirmed maternal Zika virus infection during pregnancy, a positive rRT-PCR in the infant is highly suggestive of congenital Zika virus infection even if testing was delayed.
◊ The PRNT is used to confirm the specificity of IgM antibodies detected against Zika virus and to rule out a false-positive IgM result. A positive (or "presumptive positive" or "possible positive" or "equivocal") Zika virus IgM with negative PRNT suggests a false-positive result.
§ Interpretation of the infant's results within the context of maternal testing is particularly important in this setting. In the context of confirmed maternal Zika virus infection during pregnancy, a positive IgM in the infant is highly suggestive of congenital Zika virus infection. A positive IgM in the CSF is also highly suggestive of congenital Zika virus infection.
¥ Congenital Zika virus infection is unlikely if specimens are collected within the first few days after birth and the clinical evaluation is normal; however, health care providers should remain alert for any new findings of congenital Zika virus infection.