(HealthDay News) – Antiviral resistance has been identified in some patients with a novel influenza A subtype H7N9 virus (A/H7N9), according to a study published online May 29 in The Lancet.

Yunwen Hu, MD, from the Shanghai Public Health Clinical Center, and colleagues quantified viral load and analyzed antiviral resistance mutations in specimens from 14 patients with A/H7N9.

The researchers found that all patients developed pneumonia, seven required mechanical ventilation, and three deteriorated further and required extracorporeal membrane oxygenation (ECMO). Two of these patients died. In 11 surviving patients, antiviral treatment correlated with a reduction of viral load in throat swab specimens. ECMO dependence occurred for three patients who had persistently high viral load in throat swabs, despite receiving antiviral therapy. In two of these patients, both of whom also received corticosteroid treatment, an Arg292Lys mutation was identified in the virus neuraminidase (NA) gene. In one patient, two days after treatment the wild-type sequence Arg292 was observed while the resistant mutant Lys292 dominated nine days after treatment initiation.

“Reduction of viral load following antiviral treatment correlated with improved outcome. Emergence of NA Arg292Lys mutation in two patients who also received corticosteroid treatment led to treatment failure and a poor clinical outcome,” the authors write. “The emergence of antiviral resistance in A/H7N9 viruses, especially in patients receiving corticosteroid therapy, is concerning, needs to be closely monitored, and [needs to be] considered in pandemic preparedness planning.”

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