Detecting flu at the doctor’s office

In doctor’s offices and emergency rooms, rapid flu tests can yield results in 15 minutes. These immunoassays, which use antibodies to detect influenza proteins, unfortunately produce false negatives in nearly half of flu cases. Polymerase chain reaction tests are more sensitive but often require experienced personnel, typically take hours or days to complete, and are expensive.

Researchers have now developed what could be a fast, accurate, and inexpensive alternative: an assay that uses a handheld glucose meter to detect flu virus (Chem. Sci. 2017, DOI: 10.1039/c6sc03720h).

In the assay, Suri S. Iyer of Georgia State University and coworkers treat nasal-swab samples with a synthetic conjugate of methoxylated sialic acid and galactose and apply the treated samples to glucose test strips. Neuraminidase enzyme on viruses in the samples cleaves galactose from the conjugate. This released galactose is oxidized by an enzyme on the test strip, producing a current that is measured by a glucose meter. The assay reliably detects viral infection or lack thereof in 15 minutes.

Bacteria also have neuraminidases, but those enzymes can’t recognize the conjugate. As a result, the assay distinguishes between bacteria and viruses.

Glucose meters have detected viruses before (Anal. Chem. 2012, DOI: 10.1021/ac203014s), but the conjugate is new. “The real breakthrough was finding a substrate that distinguishes between viral and bacterial neuraminidases,” says Amy Krafft, program officer for flu therapeutics and diagnostics development at the National Institute of Allergy & Infectious Diseases. The study “is a simple and clever proof of concept.”

Krafft thinks the researchers still need to assess the assay’s limits of detection and see if it can distinguish flu from other viruses. She also notes that it can’t distinguish type A from type B flu. Nevertheless, if Iyer and coworkers can optimize the test and turn it into a user-friendly kit, “it has a reasonable chance of becoming useful,” Krafft says.