The Complex Interpretation and Management of Zika Virus Test Results

Kenneth W. Lin, MD, MPH; John D. Kraemer, JD, MPH; Rachael Piltch-Loeb, MSPH; Michael A. Stoto, PhD

Disclosures

J Am Board Fam Med. 2018;31(6):924-930. 

In This Article

Abstract and Introduction

Abstract

Zika virus disease provides the latest example of a critical nexus between public health and clinical practice. Interpreting Zika virus test results is complicated by the absence of a single testing approach with superior validity across contexts and populations. Molecular tests are highly specific, variably sensitive, and have a short window period. Serologic tests identify antibodies against Zika virus and are more likely than molecular tests to cross-react with other related viruses, reducing specificity. The type of test performed and timing relative to possible Zika virus exposure depend on public health guidance, testing algorithms, test availability, and capacity. Guidance from the Centers for Disease Control and Prevention and local health departments have changed throughout the course of the US epidemic based on prevalence, geography, and clinical concerns. Women with a low pretest probability of infection should be counseled against testing. Women with a high pretest probability of Zika virus infection should still receive enhanced prenatal monitoring and newborn evaluation, regardless of the test result. An appropriate interpretation of results depends on what tests are used, patient characteristics, and reasons for testing. Clinicians should take these factors into account in shared decision making discussions with pregnant women about Zika virus testing.

Introduction

Zika virus disease provides the latest example of a critical nexus between public health and clinical practice. Clinicians rely on national recommendations and state and local health department guidance on how and when to conduct screening and diagnostic testing. Whether testing is done, which tests are used, the accuracy of results, and whether results are reported also depend on test availability, patient demand, where transmission is thought to be occurring, and public awareness of these factors. Public health guidance depends on surveillance data, which are generated primarily from case reports based on clinical tests initiated by physicians.[1] Finally, the interpretations of test results for individual patients rely on estimates of disease prevalence, which are from public health surveillance.

Clinicians have found it challenging to implement public health recommendations regarding Zika virus testing and fetal and infant surveillance,[2] and some have argued that the shifting nature of these recommendations means that clinicians cannot simply rely on algorithms from the Centers for Disease Control and Prevention (CDC) to determine whom to test.[3] This article aims to help clinicians understand the rationale for public health testing and screening guidance, the importance of appropriate testing, and how to interpret results under less than ideal circumstances. We address both screening (for asymptomatic individuals who might have been exposed) and diagnostic testing (for individuals with symptoms) and focus on women of childbearing age, because most testing scenarios that clinicians encounter will be in women who are pregnant or considering pregnancy. We begin by describing the performance of available tests and show how interpreting test results depends on 5 "Ws": who gets tested and the risk that they have been infected; what type of test is done; when the test is done; where the individual lives or has traveled; and why was the test performed (eg, in response to symptoms, known exposure, concerns about pregnancy complications, or for active surveillance purposes). These factors, in turn, influence the test's performance characteristics and the interpretation of the results for patients.

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