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Introduction of Molecular Methods

One of the first companies to bring a Food and Drug Administration (FDA) approved molecular assay to market was Prodesse. Their Hexaplex® assay was a multiplex assay for the detection of influenza A and B, parainfluenza types 1, 2, and 3, and respiratory syncytial virus (RSV). Employing RT-PCR to detect viral DNA, detection occurred as a post-amplification step, employing peroxidase labeled probes. Published studies in 2001 indicated good sensitivity and specificity, but, higher cost per test. The assay was also found to be labor intensive and lengthy.

In early 2008, the FDA approved two assays: Prodesses's ProFlu+™ and the xTAG® Respiratory Viral Panel, marketed by Luminex.

The ProFlu+™ assay is a real-time, multiplex PCR. In a closed tube system, it simultaneously detects Influenza A and B, and RSV, utilizing RT-PCR. Total turnaround time, including extraction, is approximately 3 hours.

The xTAG® assay detects more viruses. In addition to Influenza A and B, and RSV, the assay detects parainfluenza, metapneumovirus, rhinovirus, and adenovirus. The test process includes amplification by PCR, followed by analysis on a Luminex instrument. This assay provided simultaneous subtyping of Influenza H1, H3, and nonspecific types (which the Prodesse assay did not). However, turnaround time was significantly longer.

These assays helped draw an increasing interest in molecular assays for respiratory viruses in general and influenza in particular. But in many laboratories, testing protocols were completely upended in the spring of 2009, with the onset of the swine flu epidemic.