During the first week of illness, viral RNA or virus-specific immunoglobulin (Ig) M and neutralizing antibodies can often be identified in serum with RT-PCR. However, serological cross-reactivity is strong between Zika and dengue viruses, so in acute specimens, emphasis should be placed on molecular detection.
IgM antibodies against Zika virus as well as other Flaviviridae have strong cross-reactivity, and false positive results in serological tests are possible.
Serology assays can also be used to detect Zika virus-specific IgM and neutralizing antibodies, which typically develop toward the end of the first week of illness. However, IgM antibodies against Zika have strong cross-reactivity and false positive results in serological tests are possible.
Plaque-reduction neutralization testing (PRNT) can measure virus-specific neutralizing antibodies to confirm primary flavivirus infections and differentiate from other viral illnesses. However, neutralizing antibodies may yield cross-reactive results in persons who were previously infected with another flavivirus or who have received certain vaccinations.
These and more details are found in the CDC algorithm: