New test approved for influenza like illnesses

Every year "flu season" comes during which there is a marked uptick in influenza-like illnesses (ILIs) in the community. An ILI is defined to be cough or sore throat together with a fever of over 100 degrees F. (37.8 degrees C.) or self-reported fever and chills as well as no other obvious cause (e.g., strep throat). But are all ILIs influenza? No. They are ILIs. In the absence of lab work (and since most are thought to be of viral origin, only non-specific symptomatic and supportive therapy is recommended and no diagnostic lab work is usually done), an ILI could be from influenza virus or any of a number of other respiratory viruses that circulate at the same time. Now the US Food and Drug Administration (FDA) has approved a new test that differentiates 12 different respiratory viruses, including three subtypes of influenza, from one patient throat swab:

The test, called the xTAG Respiratory Viral Panel (RVP), is the first that can detect and distinguish influenza A subtypes H1 and H3 and also detect influenza B, the FDA said in announcing the approval on Jan 3. Influenza A is the most severe type of flu in humans and has been the cause of pandemics, the agency noted.

The new test panel is also the first test for human metapneumovirus (hMPV), which was first identified in 2001, the FDA said. (CIDRAP News)

It also does respiratory syncytial viruses A and B; paralinfluenza 1, 2 and 3; rhinovirus; and adenovirus. Company literature claims these represent 85% of all viral respiratory infections.

Instead of using tissue culture to isolate a virus, the new test uses polymerase chain reaction (PCR) to amplify any viral genetic material present and then employs identifiable beads coated with material specific to particular viral sequences to identify which viral genetic sequence was amplified. This eliminates both tissue culture and separate tests for each of the viruses, cutting total time down to about 6 hours instead of days. But it still requires skilled personnel and a laboratory setting. It isn't a field instrument and each specimen is estimated to cost in the hundreds of dollars.

This particular test could conceivably be part of a screen for an emerging pandemic not involving H1 or H3 subtypes. In addition, it is just the leading edge of more routine use of multiplex viral diagnostic tests. Once they are more widely employed we can expect to learn a great deal about the epidemiology of ILIs during the typical "flu season."

As regular readers here know, that's a good thing because there is a tremendous amount we don't know. It will be good to move some basic things, like what viruses circulate each winter and in what proportion, into the "we do know" column.