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Zika virus infection is diagnosed with molecular tests, which find the virus's genetic material, and serologic tests, which find the body's antibodies. Zika and dengue occur in much the same parts of the world and look alike clinically, so anyone suspected of Zika should also be evaluated for dengue. State health departments can advise on testing and help arrange it. Not every test is currently available at CDC; its Test Directory lists what it can perform.
The tests
| Test | What it tells you | Watch out for |
|---|---|---|
| NAAT (nucleic acid amplification test — any molecular test for viral genetic material) | the preferred method: a positive result can confirm infection | false positives have been reported. Zika RNA stays in serum only briefly and at low levels, so a negative NAAT does not rule out recent infection |
| IgM antibody | usually detectable from the first week after symptoms begin, and lasts months to years | antibodies cross-react with other flaviviruses, so it can be hard to tell which one caused a recent infection; false positives are more common than with NAAT |
| PRNT (plaque reduction neutralization test), which measures virus-specific neutralizing antibodies | can clear up a false-positive IgM and help identify the virus | may still fail to tell flaviviruses apart, especially after a second flavivirus infection. In a newborn it cannot separate the mother's antibodies from the baby's; by analogy with other congenital infections, maternal antibodies should be gone by 18 months of age, perhaps sooner |
CDC's detailed recommendations are in Dengue and Zika Virus Diagnostic Testing for Patients with a Clinically Compatible Illness and Risk for Infection with Both Viruses. The guidance below is updated as Zika's spread changes; local, state and territorial health departments advise on testing and sending specimens.
No confirmed cases of Zika virus disease have been found in the United States or its territories since 2018. Exposure categories below refer to CDC's Zika Travel Health Notices and its list of areas with current or past Zika transmission.
Pregnant, no symptoms
| Exposure during pregnancy | Guidance |
|---|---|
| lived in or traveled to the United States or its territories | routine testing not recommended |
| traveled to an area with an active Zika Travel Health Notice | NAAT may be considered up to 12 weeks after travel |
| traveled to an area outside the U.S. with current or past Zika transmission | routine testing not recommended; if you decide to test, NAAT up to 12 weeks after travel |
CDC's July 2017 interim guidance explains its shared decision-making approach to testing and screening pregnant women.
Pregnant, with symptoms
In every case, collect specimens as soon as possible after symptoms start, and up to 12 weeks after.
Lived in or traveled to an area with an active Travel Health Notice — or had sex with someone living there or recently back from one:
- Serum: dengue and Zika NAAT and IgM. Urine: Zika NAAT.
- Zika NAAT positive but Zika IgM negative → repeat the NAAT on newly extracted RNA from the same specimen, to rule out a false positive.
- Both NAATs negative but either IgM positive → confirmatory PRNTs against dengue, Zika and other flaviviruses found where the exposure happened.
Lived in or traveled to an area with current or past Zika transmission:
- Serum: dengue and Zika NAAT. Urine: Zika NAAT.
- Zika NAAT positive → repeat on newly extracted RNA from the same specimen.
- IgM for dengue only. A positive dengue NAAT or IgM is enough evidence of dengue; no further testing.
Had sex with someone living in or recently back from an area with current or past transmission:
- Zika NAAT only.
- Positive → repeat on newly extracted RNA from the same specimen.
Pregnant, with ultrasound findings suggesting congenital Zika
For exposure — by living, travel or sex — linked to an area with an active Travel Health Notice or current or past transmission:
- Serum: Zika NAAT and IgM. Urine: Zika NAAT.
- NAATs negative, IgM positive → confirmatory PRNTs against Zika and dengue.
- If amniocentesis is done for clinical care, test the fluid by Zika NAAT too, and read the result in light of the limits of amniotic fluid testing.
- Placental and fetal tissue testing may also be considered — see collecting and submitting those specimens.
Not pregnant
| Situation | Guidance |
|---|---|
| No symptoms | dengue or Zika testing not recommended |
| Symptoms, living in or recently back from the United States or its territories | routine testing not recommended |
| Symptoms, living in or recently back from an area outside the U.S. with an active notice or current or past transmission | serum within 7 days of symptom onset: dengue and Zika NAAT — a positive usually means acute infection. NAAT-negative serum, or serum taken after 7 days: dengue and Zika IgM. If either IgM is positive and a definite diagnosis is needed for clinical or public health reasons: confirmatory PRNTs against dengue, Zika and the region's other flaviviruses |
Infants with possible congenital Zika
When the mother may have been exposed during pregnancy:
- Collect specimens as soon as possible after birth.
- Infant serum: Zika NAAT and IgM. Infant urine: Zika NAAT.
- If cerebrospinal fluid is taken for another reason, test it by NAAT and IgM as well.
- Infant serum IgM non-negative and NAAT negative, with no PRNT done on the mother's serum → PRNT for Zika and dengue on the infant's serum.
- If the birth sample was IgM non-negative and PRNT found neutralizing antibodies in the infant's or mother's sample → PRNT on a sample taken at 18 months or older.
More: CDC's October 2017 interim guidance on diagnosing, evaluating and managing infants with possible congenital Zika infection.
Sources
Based on "Clinical Testing and Diagnosis for Zika Virus Disease," Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licença: CC0 1.0 (domínio público) · Adaptado de www.cdc.gov
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