Testing Types
Patient Groups
Testing Types
Nucleic Acid Amplification Test (NAAT)
- Generic term referring to all molecular tests used to detect viral genomic material
- Preferred method of diagnosis because it can provide confirmed evidence of infection
Limitations:
- Due to the short period and low level of Zika virus RNA in serum, a negative NAAT does not exclude recent Zika infection
- False positive NAAT results have been reported
Zika virus immunoglobulin (Ig) M antibody testing
- Recommended in the first week after onset of symptoms
- Can persist for months up to years
Limitations:
- Can cross-react with other flavivirus antibodies
- False-positive results are more common with IgM than NAAT
Plaque reduction neutralization tests (PRNT)
- Measure virus-specific neutralizing antibody titers
- May resolve false-positive IgM antibody results caused by non-specific reactivity
- Useful in identifying the infecting virus
Limitations:
- May not discriminate between flaviviruses antibodies, especially following secondary flavivirus infections due to cross-reactivity
- Cannot distinguish between maternal and infant antibodies in specimens collected at or near birth
- Maternal antibodies may persist in the infant's system and typically become undetectable by 18 months of age, though they might wane earlier
Specific Patient Groups
Asymptomatic pregnant women
- For asymptomatic pregnant women living in or with recent travel to the U.S. and its territories, routine Zika virus testing is NOT currently recommended.
- For asymptomatic pregnant women with recent travel to an area with an active CDC Zika Travel Health Notice outside the U.S. and its territories during pregnancy, NAAT testing may be considered up to 12 weeks after travel.
- For asymptomatic pregnant women with travel to an area with current or past Zika virus transmission outside the US and its territories during pregnancy, routine testing is NOT recommended. If the decision is made to test, NAAT testing can be done up to 12 weeks after travel.
Symptomatic pregnant women
For symptomatic pregnant women who lived in or traveled to an area with an active CDC Zika Travel Health Notice during pregnancy OR had sex during pregnancy with someone living in or with recent travel to an area with an active CDC Zika Travel Health Notice
- Specimens should be collected as soon as possible after onset of symptoms up to 12 weeks after symptom onset.
- Perform dengue and Zika virus NAAT and IgM testing on a serum specimen and Zika virus NAAT on a urine specimen.
- If Zika NAAT is positive and the Zika IgM is negative, repeat NAAT test on newly extracted RNA from same specimen to rule out false-positive 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.
For symptomatic pregnant women who lived in or traveled to an area with current or past Zika virus transmission during pregnancy
- Specimens should be collected as soon as possible after onset of symptoms up to 12 weeks after symptom onset.
- Perform dengue and Zika virus NAAT testing on a serum specimen and Zika virus NAAT on a urine specimen.
- If Zika NAAT is positive, repeat test on newly extracted RNA from same specimen to rule out false-positive results.
- Perform IgM testing for dengue only.
- If dengue NAAT or IgM is positive, this provides adequate evidence of dengue infection, and no further testing is indicated.
For symptomatic pregnant women who had sex during pregnancy with someone living in or with recent travel to an area with current or past Zika virus transmission:
- Specimens should be collected as soon as possible after onset of symptoms up to 12 weeks after symptom onset.
- Only Zika NAAT should be performed.
- If Zika NAAT is positive, repeat test on newly extracted RNA from same specimen to rule out false-positive results.
Fetus with congenital Zika virus infection
Pregnant women who have a fetus with prenatal ultrasound findings consistent with congenital Zika virus infection, and:
lived in or traveled during pregnancy to areas with an active CDC Zika Travel Health Notice or current or past Zika virus transmission
OR had sex during pregnancy with someone living in or with recent travel to an area with an active CDC Zika Travel Health Notice or current or past Zika virus transmission
- Zika virus NAAT and IgM testing should be performed on pregnant woman's serum and NAAT on pregnant woman's urine.
- If the Zika virus NAATs are negative and the IgM is positive, confirmatory PRNTs should be performed against Zika and dengue.
- 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.
- Testing of placental and fetal tissues may also be considered (see guidance for Collecting & Submitting Placental and Fetal Tissue Specimens for Zika Virus Testing)
Symptomatic non-pregnant patient
For symptomatic non-pregnant patients living in or with recent travel to the United States and its territories:
- routine Zika virus testing is not recommended.
For symptomatic non-pregnant patients living in or with recent travel to an area with an active CDC Zika Travel Health Notice or current or past Zika virus transmission outside the US and its territories:
- Dengue and Zika virus NAATs should be performed on serum collected ≤7 days after symptom onset. A positive NAAT result typically provides evidence of acute infection.
- Perform dengue and Zika virus IgM antibody testing on NAAT-negative serum specimens and serum collected >7 days after onset of symptoms.
- If either dengue or Zika virus IgM antibody testing is positive, and definitive diagnosis is needed for clinical or epidemiologic purposes, confirmatory PRNTs should be performed against dengue, Zika and other flaviviruses endemic to the region where exposure occurred.
Asymptomatic non-pregnant patient
- Testing for dengue or Zika viruses is not recommended.
Infant with possible congenital Zika virus infection
With a mother with possible Zika virus exposure during pregnancy:
- Collect specimens as soon as possible after birth.
- Zika virus NAAT and IgM testing should be performed on infant serum and NAAT on infant urine.
- If cerebrospinal fluid (CSF) is obtained for other purposes, NAAT and IgM antibody testing should be performed on CSF.
- If the infant's serum is IgM non-negative and NAAT negative, but PRNT was not performed on the mother's serum, PRNT for Zika and dengue viruses should be performed on the infant serum.
- Perform PRNT on a sample collected from an infant aged 18 months or older whose initial sample collected at birth was IgM non-negative and neutralizing antibodies were detected by PRNT in either the infant's or mother's sample.
