Study outlines H7N9 antiviral resistance, testing problems

Wednesday, July 17, 2013
By Paul Martin

Lisa Schnirring
Jul 16, 2013

A new analysis of the H7N9 virus from the first known case in China’s ongoing outbreak found that signs of antiviral resistance weren’t flagged by regular sensitivity testing, which could prevent detection and allow resistant strains to spread, a research team reported today.

A number of the viruses the team grew from the strain obtained from a patient in Shanghai had a mutation linked to resistance to the neuraminidase inhibitors oseltamivir, zanamivir, and peramivir, which are considered the frontline treatments for the often-severe H7N9 infections. Resistance to M2 ion channel blockers, another class of antivirals, has already been found in H7N9 isolates.

Researchers from China, Hong Kong, Australia, and St. Jude Children’s Research Hospital in Memphis reported their findings in the latest issue of mBio, the online journal of the American Society for Microbiology (ASM).

The group’s worrisome findings about H7N9 antiviral resistance echo other findings reported from both clinical settings and lab studies. In the middle of April, about 2 weeks after the outbreak emerged, one of the first genetic analyses of H7N9 viruses from the initial confirmed cases found a neuraminidase inhibitor resistance marker in one of the three strains.

In early May a clinical report on four severely ill H7N9 patients treated at a Shanghai hospital aired early suspicions about oseltamivir failures in two of the patients. Later that month a team looking for evidence of antiviral resistance in 14 hospitalized Shanghai patients who received oseltamivir found a known resistance marker in those who didn’t respond to treatment and had a poor prognosis.

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