Zika virus diagnosis is crucial, especially for vulnerable populations such as pregnant women. Accurate and timely diagnosis is essential for appropriate medical management and public health interventions. This guide provides a detailed overview of the diagnostic approaches for Zika virus infection, based on the latest recommendations.
Understanding Zika Virus Diagnostic Tests
Nucleic acid amplification tests (NAATs) are the primary diagnostic method for Zika virus. These molecular tests detect the virus’s genetic material, offering direct evidence of infection. Despite their high specificity, false-positive NAAT results can occur, necessitating careful interpretation.
Zika virus immunoglobulin (Ig)M antibody testing plays a supporting role in diagnosis. IgM antibodies typically appear in the first week after symptom onset and can persist for months or even years. However, IgM tests can be less definitive due to cross-reactivity with antibodies from other flaviviruses like dengue. False-positive IgM results are also more frequent than with NAATs.
Plaque reduction neutralization tests (PRNTs) are used to resolve ambiguous IgM results. PRNTs measure virus-specific neutralizing antibodies and can help differentiate between Zika and other flavivirus infections. However, PRNTs may still face challenges in distinguishing between flaviviruses, particularly after secondary infections. In infants, PRNT cannot differentiate between maternal and infant antibodies in early samples.
Alt: Algorithm for Zika virus diagnostic testing, showing NAAT, IgM, and PRNT testing pathways based on symptom onset and test results.
Zika Virus Testing Guidelines for Asymptomatic Pregnant Patients
Routine Zika virus testing is generally not recommended for asymptomatic pregnant women in the United States and its territories, as no confirmed cases have been reported since 2018 within these regions.
For pregnant women who traveled to areas with an active CDC Zika Travel Health Notice during pregnancy, NAAT testing might be considered within 12 weeks of return.
Pregnant women who traveled to areas with current or past Zika virus transmission outside the US territories, routine testing is not advised. However, if testing is pursued, NAAT can be performed up to 12 weeks post-travel.
Zika Virus Testing Guidelines for Symptomatic Pregnant Patients
For symptomatic pregnant women who lived in or traveled to an area with an active CDC Zika Travel Health Notice, or had sexual contact during pregnancy with someone with such travel history, prompt testing is recommended. Specimens should be collected as soon as symptoms appear, up to 12 weeks after onset.
The recommended tests include dengue and Zika virus NAAT and IgM testing on serum, and Zika virus NAAT on urine. If Zika NAAT is positive and IgM is negative, repeat NAAT on a new RNA extraction to exclude false positives. In cases where both dengue and Zika NAATs are negative, but either IgM is positive, confirmatory PRNTs for dengue, Zika, and other regional flaviviruses are necessary.
Alt: Diagnostic algorithm for symptomatic pregnant women and Zika virus, detailing NAAT and IgM testing for serum and urine samples based on travel history and exposure risk.
For symptomatic pregnant women with travel history to areas with current or past Zika transmission, dengue and Zika virus NAAT on serum and Zika NAAT on urine should be performed within 12 weeks of symptom onset. If Zika NAAT is positive, repeat the test on a new RNA extraction. IgM testing is indicated for dengue only. Positive dengue NAAT or IgM is sufficient for dengue diagnosis, and no further Zika testing is needed in this scenario if Zika NAAT is negative.
For symptomatic pregnant women who had sexual contact with someone who lived in or traveled to areas with current or past Zika transmission, Zika NAAT is the recommended test. If positive, repeat the NAAT on a newly extracted RNA sample.
Zika Virus Testing for Fetuses with Ultrasound Findings Suggestive of Congenital Zika Infection
For pregnant women carrying a fetus with prenatal ultrasound findings indicative of congenital Zika virus infection, and with a history of travel to or residence in Zika-affected areas, or sexual contact with someone with such history, specific testing protocols apply.
Zika virus NAAT and IgM testing on serum, and NAAT on urine are recommended. If Zika NAATs are negative but IgM is positive, confirmatory PRNTs against Zika and dengue are needed. If amniocentesis is performed, Zika virus NAAT on amniotic fluid should also be conducted, with careful interpretation of results due to the limitations of amniotic fluid testing. Placental and fetal tissue testing can also be considered.
Zika Virus Testing Guidelines for Symptomatic Non-Pregnant Patients
Routine Zika virus testing is not recommended for symptomatic non-pregnant individuals living in or recently traveling within the United States and its territories due to the absence of confirmed cases since 2018.
For symptomatic non-pregnant individuals living in or recently traveling to areas with an active CDC Zika Travel Health Notice or current/past Zika transmission outside the US territories, dengue and Zika virus NAATs on serum collected within 7 days of symptom onset are recommended. A positive NAAT result is generally indicative of acute infection.
For NAAT-negative serum samples, and for serum collected more than 7 days after symptom onset, dengue and Zika virus IgM antibody testing should be performed. If either dengue or Zika IgM is positive and a definitive diagnosis is required for clinical or epidemiological reasons, confirmatory PRNTs against dengue, Zika, and other regional flaviviruses should be conducted.
Zika Virus Testing Guidelines for Asymptomatic Non-Pregnant Patients
Testing for dengue or Zika viruses is not recommended for asymptomatic non-pregnant individuals.
Zika Virus Testing Guidelines for Infants with Possible Congenital Zika Virus Infection
For infants with possible congenital Zika virus infection born to mothers with potential Zika exposure during pregnancy, testing should be initiated as soon as possible after birth.
Recommended tests include Zika virus NAAT and IgM testing on infant serum, and NAAT on infant urine. If cerebrospinal fluid (CSF) is obtained for other reasons, NAAT and IgM antibody testing on CSF should also be performed.
If infant serum IgM is non-negative and NAAT is negative, but maternal PRNT was not done, infant serum PRNT for Zika and dengue is necessary. For infants older than 18 months whose initial sample at birth was IgM non-negative and neutralizing antibodies were detected by PRNT in either infant or mother’s sample, PRNT should be repeated.
In conclusion, diagnosis of Zika virus infection relies on a combination of NAAT, IgM, and PRNT assays, interpreted in the context of the patient’s symptoms, pregnancy status, travel history, and potential exposures. These guidelines are essential for healthcare providers in accurately diagnosing and managing Zika virus infections.
