FDA, CDC, and tests steer flu Dx into new season

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Dr. Arcenas

It’s very useful for laboratories to establish benchmarks and metrics on their influenza testing, Dr. Arcenas says. When his laboratory in Hollywood, Fla., first brought in molecular testing for respiratory viruses, “We put out to our clinicians for a couple of years a viral prevalence report to give them an idea of what’s circulating in the patient community and coming into our hospitals. Then it really dawned on us, since we serve pediatrics as well as the adult side, to compare data on them in a virogram. And we found some interesting things. This year there is an earlier occurrence of influenza A in adults where it seemed to be lagging in pediatrics.” Now, pediatric numbers are creeping up, Dr. Arcenas says, “and we’re also seeing an earlier incidence of RSV and higher incidence of co-infections in pediatrics and adults.”

He and colleagues published an article on inappropriate and obsolete clinical laboratory tests, which focused on rapid antigens and how they’re suboptimal in performance (Kiechle FL, et al. Clin Chim Acta. 2014 [Jan. 1];427:131–136). “I guess it’s hard for pediatric clinicians to get rid of the rapid tests. In their defense, a positive result does help them out and for molecular they have to wait at least a day. But negative results don’t help at all. And that’s kind of an issue here.”

On the adult side, clinicians tend not to order a lot of rapid antigen tests, he says. “If the patient has the flu, they go ahead and treat it, and they get the extensive molecular panel if they’re going to admit the patient or if they have someone who is immunocompromised.”

Dr. Arcenas expects to see more tests emerge soon to occupy the middle ground between rapid antigen tests and the full-blown molecular panels. “Some companies are already offering FDA-approved ‘direct-to-answer’ molecular tests, where you can actually test the sample. You don’t have to do any kind of nucleic acid extraction or set up a PCR master mix,” he says. “You just put in the sample, it goes through the reverse transcriptase PCR reaction, then detection, and you get a result in one or two hours. It primarily targets more common viruses like influenza A and B, and RSV, which are the ones that really have treatment implications where a rapid test matters.”

The FDA is proposing to reclassify waived rapid tests, he adds, because of the poor performance of the tests. “Of course, you have to really monitor the tests each year because the virus does change, and class II classification should be a way to have these companies that make the RIDT be more vigilant in making sure their assay is performing up to their claims.”

In the meantime, Dr. Arcenas continues working at his hospital to get clinicians to understand the limitations of the rapid tests. “We had a lot of success during the 2009 H1N1 outbreak when all those papers came out on poor performance. So we had many clinicians treating symptoms as flu and ordering the full-blown panel we were offering if warranted. For some of our high-risk patients on the pediatric side, I think just because of the nature of the disease state, they will go ahead and get the whole panel to cover. So they’re slowly switching, but the need for the panels is still not completely recognized.”

Despite the emergence of rapid molecular assays, the cost of molecular testing for influenza will need to drop for molecular tests to compete with RIDTs, the CDC’s Dr. Jernigan says. “As these molecular assays become more automated or simplified, the price point has to be lower. But overall, over the next year we look forward to seeing some promising new technologies coming out that we think will improve the diagnosis of influenza.”[hr]

Anne Paxton is a writer in Seattle.