Clinical Testing and Diagnosis for Zika Virus Disease

Nucleic acid amplification test, or NAAT, is a generic term referring to all molecular tests used to detect viral genomic material. NAAT assays are the preferred method of diagnosis because they can provide confirmed evidence of infection. Despite the specificity of molecular testing, false positive NAAT results have been reported.

Because of the short period and low level of Zika virus RNA in serum, a negative NAAT does not exclude recent Zika infection. For this reason, Zika virus immunoglobulin (Ig) M antibody testing is recommended in certain situations. IgM generally is detectable starting in the first week after onset of symptoms and persists months to years. IgM testing is complicated by cross-reactive antibodies to other flaviviruses, which might make conclusive determination of which flavivirus is responsible for the person's recent infection difficult. False-positive results are more common with IgM than NAAT and can occur due to non-specific reactivity or cross-reactivity with other flaviviruses.

Plaque reduction neutralization tests (PRNT) measure virus-specific neutralizing antibody titers. PRNTs may resolve false-positive IgM antibody results caused by non-specific reactivity and help identify the infecting virus. However, due to cross-reactivity, PRNT might not discriminate between flaviviruses antibodies, especially following secondary flavivirus infections.

For infant diagnosis, PRNT cannot distinguish between gestational parent and infant antibodies in specimens collected from infants at or near birth. Based on what is known about other congenital infections, gestational parent antibodies are expected to become undetectable by 18 months of age and might become undetectable earlier.

Resource‎

Below is a summary of CDC's Zika testing guidance. It will be updated as needed to address the epidemiology of Zika virus. Healthcare providers are encouraged to contact their local, state or territorial health departments for guidance on Zika testing and submitting specimens in their respective states.

Asymptomatic pregnant patient

• Since no confirmed cases of Zika virus disease have been detected in the United States and its territories since 2018, routine Zika virus testing is not recommended.

• NAAT testing may be considered up to 12 weeks after travel.

Traveled 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 patient

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.

• 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 test is positive, this provides adequate evidence of dengue infection, and no further testing is indicated.

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.
  

Interim Guidance for Health Care Providers Caring for Pregnant Women with Possible Zika Virus Exposure — United States (Including U.S. Territories), July 2017‎

Read more about CDC's shared decision-making model for testing and screening pregnant women for Zika virus infection.

Pregnant patient having a fetus with prenatal ultrasound findings consistent with congenital Zika virus infection

Lived in or traveled during pregnancy to an area 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 person's serum and NAAT on pregnant person'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.

Symptomatic non-pregnant patient

• Since no confirmed cases of Zika virus disease have been detected in the United States and its territories since 2018, routine Zika virus testing is not recommended.