Tracking the development of drug resistance in flu outbreaks is vital to determine treatment and make public health decisions, and a team of researchers in China is using the polymerase chain reaction (PCR) to spot mutant strains.

Dynamic range of reverse transcription PCR for detection of oseltamivir resistance in influenza A (H7N9) virus

Dynamic range of reverse transcription PCR for detection of oseltamivir resistance in influenza A (H7N9) virus

Overall, resistance to Tamiflu (oseltamivir), used to treat influenza (including bird flu), is fortunately still fairly rare. However, in the Chinese outbreak of avian influenza (bird flu – H7N9) in March 2013, there was an unusually high proportion of severe cases and a high fatality rate, according to the researchers in the journal Emerging Infectious Diseases. By October 2013, there had been 137 laboratory-confirmed cases and 45 deaths.

The Chinese team had seen emergence of the R292K PCR (RT-PCR) to spot the mutant virus amongst the normal (wild-type) R292 virus in clinical samples.

The assay created by the Chinese researchers used two reactions, one with a FAM-labelled SNP probe specific for the 292K mutant strain and a second reaction contained a VIC-labelled probe specific for the R292 wild-type strain. When the team tested the sensitivity of the assay, using 35 respiratory samples from patients with a variety of different viruses (including the mutant and wild-type strains), they found that the assay was highly specific for detecting the mutant strain of the influenza A (H7N9) virus. The assay was also able to detect the mutant strain in samples containing both the mutant and wild-type version of H7N9.

The viral load was higher in sputum samples compare with nasal swabs, which suggested that the virus might replicate better in the lung compared with the nose and throat. When the assay was used to screen samples over time, after starting antiviral treatment, the researchers saw signs of the virus mutating under the pressure of antiviral treatment, leading to a failure of the virus to clear the lower respiratory tracts.

According to the researchers, this could be a sensitive, fast, specific and low-cost screening tool, and could be used to monitor emergence of drug-resistant virus strains during treatment of patients with antiviral drugs to prevent persistent viral replication and severe inflammatory reactions.