September 05, 2017
2 min read

Novel rapid tests improve influenza diagnosis

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Results of a recent systematic review and meta-analysis showed that two novel classes of rapid influenza diagnostic tests have similar specificities but higher sensitivities than traditional rapid tests.

According to Joanna Merckx, MD, MSc, of the department of epidemiology, biostatistics and occupational health at McGill University, and colleagues, rapid influenza diagnostic tests (RIDTs) are widely used over reverse transcriptase-PCR, the “gold standard” for diagnosing influenza, because they are simple to use in the point-of-care setting and provide results in under 30 minutes. There are two novel classes of RIDTs — digital immunoassays (DIAs), which digitally scan test strips to enhance antigen detection accuracy, and rapid nucleic acid amplification tests (NAATs), which use a modified RT-PCR or isothermal amplification technology — that have been on the market since 2011, with claims of having higher sensitivities than traditional RIDTs.

In February, the FDA reclassified minimum performance standards for RIDTs. The researchers stated that the new standards, which will be effective December 2018, require tests to perform with a sensitivity of at least 80% compared with reverse transcriptase-PCR.

In light of these new recommendations, Merckx and colleagues conducted a systematic review and meta-analysis of 162 studies published up to May 2017 to compare the efficacy of RIDTs with RT-PCR. Most of the studies (80.2%) investigated the accuracy of traditional RIDTs, followed by DIAs (11.7%) and NAATIs (8%).

The overall pooled specificity was high (at least 98.3%) across the test classes. Sensitivities, however, varied. For influenza A, the pooled sensitivities were 91.6% (95% CI, 84.9%-95.9%) for NAATs, 80% (95% CI, 73.4%-85.6%) for DIAs, and 54.4% (95% CI, 48.9%-59.8%) for traditional RIDTs. For influenza B, pooled sensitivities were 95.4% (95% CI, 87.3%-98.7%) for NAATs, 76.8% (95% CI, 65.4%-85.4%) for DIAs, and 53.2% (95% CI, 41.7%-64.4%) for traditional RIDTs.

Further analyses showed that pooled sensitivities were generally higher in children (12.1%-31.8%) than in adults. However, the researchers noted that incomplete reporting resulted in an unclear risk of study bias and limited the exploration of heterogeneity.

“The results ... suggest that traditional RIDTs are likely to be phased out by regulatory agencies like the FDA because of their poor sensitivity, especially in adults,” Merckx and colleagues concluded. “Additional clinical impact and cost-effectiveness analyses of DIAs and NAATs should help guide decisions about applying rapid testing for influenza in clinical practice.”

In a related editorial, Michael G. Ison, MD, MS, of Northwestern University Feinberg School of Medicine, Chicago, said the results show that DIAs and rapid NAATs have the “appropriate characteristics” needed to improve influenza diagnosis, which, in turn, will likely improve early antiviral use and reduce unnecessary antibiotic therapy.

“The data provided in Merckx and colleagues’ review should prompt revision of guidelines to encourage use of these newer diagnostic strategies,” he wrote. “Although studies are needed to confirm the utility of these assays in the point-of-care setting and to optimize their implementation and use, the strength of the data suggests that now is the time to utilize these newer tests to help clinicians make better antimicrobial choices for patients with influenza infection.” – by Stephanie Viguers

Disclosure: Ison reports receiving grants and/or personal fees from Beckman Coulter, Celltrion, Cepheid, Chimerix, Farmark, Genentech/Roche, Gilead, GlaxoSmithKline, Janssen, Seqirus, Shionogi, Shire, Toyama/MediVectro. Merckx reports receiving investigator-initiated funding from BD Diagnostic Systems. Please see the full study for a list of all other authors’ relevant financial disclosures.