Because viremia occurs from several days before symptom and continues for a week afterwards, real-time RT-PCR (rRT-PCR) of serum, urine, or spinal fluid can provide definitive diagnosis; however, a negative test does not rule out Zika virus. The urine test is positive up to two weeks following symptoms.
If the nucleic acid test is negative, an ELISA IgM test can be performed. If positive, a plaque reduction neutralization test (PRNT) should be performed, because there is cross-reactivity with related flaviviruses, especially dengue. There can also be cross-reaction with yellow fever, St. Louis encephalitis and West Nile virus.
Pregnant women who have Zika virus symptoms less than two weeks previously should have urine and serum tested with rRT-PCR. If it is more than two weeks but less than 12 weeks or if the rRT-PCR is negative, IgM antibody should be tested.
The following table is from the Interim Guidance for Interpretation of Zika Virus Antibody Test Results from MMWR 2016:65.32
32. Rabe IB, Staples JE, Villanueva J, et al. Interim guidance for interpretation of Zika virus antibody test results. MMWR Morb Mortal Wkly Rep 2016;65. Accessed October 25, 2022. https://pubmed.ncbi.nlm.nih.gov/27254248/
