Exactly how to screen for and, thus, diagnose Zika virus remains a bit of a moving target for clinicians as the risk for localized transmission of the mosquito-borne disease rises for some parts of the United States with the arrival of summer.
Which is at least in part why the recent directive
from the Centers for Disease Control and Prevention (CDC) with regard to IgM antibody testing for the virus has been met with a certain amount of skepticism. On June 21, the CDC announced its latest guidance with regard to IgM antibody testing, and several experts have told Contagion
that they question the “practicality” of many aspects of the document.
According to the CDC, clinicians with patients possibly exposed to the Zika virus (i.e., who have travelled to areas with ongoing outbreaks, such as Brazil or Puerto Rico, or those who have come in sexual contact with such individuals) and who have symptoms consistent with the disease should submit serum samples collected from the patients for real-time reverse-transcription polymerase chain reaction (rRT-PCR) molecular assays. However, although studies have shown that rRT-PCR can be used to confirm a Zika diagnosis and differentiate cases from those involving similar viruses such as Dengue fever, and most commercial laboratories in the United States have the necessary technology to perform it, it is hardly fool-proof. For this reason, the CDC also advises clinicians “to retain and store in a refrigerator” (at 2°C to 8°C) an “aliquot of the patient’s serum for subsequent IgM enzyme-linked immunosorbent assay” (ELISA) in cases in which rRT-PCR is not sufficient to confirm diagnosis.
Unfortunately, it’s not clear how many commercial medical testing laboratories in the United States are equipped to provide IgM ELISA testing now, or in the near future. In addition, if the labs acquired the technology in the short term, James D. Cherry, MD, MSc, professor of pediatrics at the David Geffen School of Medicine at UCLA, says it is still unknown whether ELISA “adequately separates Dengue antibody from Zika antibody.”
Worse, and not surprisingly, there are additional concerns regarding the saving and storing of samples for future analysis. Dr. Cherry told Contagion
that hospitals and commercial labs “don’t like” to store samples—typically due to the costs and the lack of appropriate space—and may only be able to do so for a short period of time.
The CDC guidance does account for situations in which samples cannot be—or simply were not—stored, advising clinicians to collect a second serum specimen within 12 weeks of symptom onset for Zika IgM ELISA testing. According to the CDC, appropriate samples for molecular testing include “serum samples collected <7 days and urine samples collected <14 days after symptom onset.”
If that sounds like a “Plan B,” that’s because it pretty much is. But having a Plan B is better than having no plan at all
for Zika, particularly as the true nature of the virus and the threat it poses globally is still to be determined.
Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.
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