Because viremia occurs several days before symptoms and continues for a week afterward, real-time RT-PCR (rRT-PCR) of serum, urine, or spinal fluid can provide a definitive diagnosis; however, a negative test does not rule out the Zika virus. The urine test is positive for 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-reactivity with yellow fever, St. Louis encephalitis, and West Nile virus.
Pregnant patients 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.
