Unusual Laboratory Results Suggest Late Development of Zika Virus-Specific Neutralizing Antibodies

Zika virus is an emerging infectious disease that is not yet fully understood. Laboratory testing guidelines were established based on research on related flaviviruses, such as dengue. However, recent evidence has suggested differences in immunological response to infections between dengue and Zika virus. Interim US Centers for Disease Control and Prevention (CDC) guidance in interpretation of Zika laboratory test results cannot cover every possible scenario. Here, we present a case of an asymptomatic patient with conflicting laboratory results from a specimen drawn 8 days after moving to the USA from an area of Zika risk. The patient was found to be both positive and negative for Zika virus RNA by different laboratories, positive for Zika-specific IgM antibodies and negative for Zika-specific and dengue-specific neutralizing antibodies. Because this specimen was drawn shortly after a potential exposure, we hypothesized that the patient had been infected, but had yet to develop neutralizing antibodies against Zika. After drawing a new specimen approximately 9 weeks after the original, the patient was found to have neutralizing antibodies, suggesting that she had been recently infected with Zika virus. This case illustrates that patients with unusual laboratory results should be considered in the context of their potential risk factors and the nuances of interpreting laboratory testing. J Med Cases. 2018;9(9):281-283 doi: https://doi.org/10.14740/jmc3029w