Emergency Action to Expand US Zika Testing Capacity

The U.S. Food and Drug Administration has granted emergency use authorization for a new laboratory test to detect Zika virus, a move aimed at significantly expanding testing capacity across the nation’s public health laboratories.

The authorization, announced by the Centers for Disease Control and Prevention on February 26, 2016, allows the CDC’s Zika IgM antibody capture enzyme-linked immunosorbent assay (Zika MAC-ELISA) to be used in qualified laboratories under emergency conditions. This test detects antibodies produced by the immune system in response to Zika virus infection, providing a critical tool for diagnosing recent or current infection, particularly in pregnant women and individuals with symptoms consistent with Zika virus disease.

Prior to this authorization, testing for Zika virus was largely restricted to a limited number of CDC laboratories and a few state public health labs, creating bottlenecks as concerns grew over the virus’s spread, particularly in relation to its association with microcephaly and other severe fetal brain defects. The emergency use authorization enables broader deployment of the test to additional Laboratory Response Network (LRN) laboratories, enhancing the ability of state and local health departments to conduct timely surveillance and diagnostic testing.

The Zika MAC-ELISA test is designed to detect immunoglobulin M (IgM) antibodies, which typically appear in the blood within days of symptom onset and can remain detectable for up to 12 weeks. While the test is not intended to detect the virus directly, it serves as an important serological marker for recent infection, especially when molecular testing via reverse transcription-polymerase chain reaction (RT-PCR) is no longer feasible due to the clearance of viral RNA from the bloodstream.

Health officials emphasized that the test requires careful interpretation, as IgM antibodies can sometimes cross-react with antibodies produced in response to other flaviviruses, such as dengue or yellow fever. To address this, the CDC recommends that positive or equivocal results from the Zika MAC-ELISA be followed by additional testing, such as plaque reduction neutralization tests (PRNT), to confirm specificity and rule out cross-reactivity.

The emergency use authorization does not constitute full FDA approval but allows the test to be used during public health emergencies when no adequate, approved, and available alternatives exist. Under this framework, laboratories performing the test must adhere to specific protocols, including staff training, quality control measures, and reporting requirements to the CDC and FDA.

In conjunction with the authorization, the CDC issued updated guidance for healthcare providers on evaluating patients for possible Zika virus infection, particularly those with recent travel to areas with active Zika transmission or potential sexual exposure. The guidance outlines when to consider testing based on symptoms, pregnancy status, and exposure history, reinforcing the importance of timely diagnosis in preventing adverse outcomes.

As of the announcement, local transmission of Zika virus had been reported in multiple U.S. Territories, including Puerto Rico, the U.S. Virgin Islands, and American Samoa, with growing concern about the potential for limited local spread in parts of the continental United States, particularly in regions where the Aedes aegypti mosquito—the primary vector for Zika—is established.

The expansion of testing capacity through this emergency authorization reflects a coordinated federal response to strengthen domestic preparedness against emerging infectious diseases. Public health officials continue to monitor the situation closely, emphasizing surveillance, mosquito control, and public education as key components of the ongoing response to Zika virus.