Oseltamivir-resistant H1N1 may spread

A recent study showed that a cluster of 2009 H1N1 virus cases that were resistant to oseltamivir and responsible for illnesses in Australia last year maintained their fitness when the resistance mutation was present.

The study suggests that widespread emergence of the resistant strain could be more likely due to the stability of the viruses in the presence of the mutation. The researchers identified 29 2009 H1N1 viruses that contained the H275Y resistance mutation between May and October in the country's Hunter New England region. Some of the patients had family or other contacts infected with the same strain and only one of them had been treated with oseltamivir, CIDRAP News reports.

The scientists interviewed patients infected with the virus to assess antiviral and medical treatment history. They tested samples for the H275Y mutation and sensitivity to neuraminidase inhibitors and found that 26 of the 29 patients infected with the resistant strains lived in five adjacent towns. The H275Y variants were virtually identical, suggesting they emerged from one source.

The researchers said that the 2009 H1N1 virus might be changing to become more tolerant of the H275Y mutation than when it first came about. This could result in the widespread emergence of viruses that are oseltamivir-resistant, CIDRAP News reports.

Alicia Fry and Larisa Gubareva said that due to a shortage of treatment options, it is important to note that the researchers found evidence that the resistant Australian viruses may be less resistant to oseltamivir than resistant strains of the former seasonal H1N1 viruses were.

"This raises the question of whether oseltamivir might retain some clinical effectiveness against infections caused by H1N1pdm09 virus with the H275Y substitution and that oseltamivir might remain a treatment option, at least for persons without severe illness," Fry and Gubareva said, according to CIDRAP News.