Australia: Oseltamivir-resistant 2009 H1N1 virus Update

CIDRAP: An oseltamivir-resistant 2009 H1N1 virus that spread in one Australian community in 2011 apparently did not escape to a nearby large city, according to a report published in Eurosurveillance yesterday. Researchers previously reported the community spread of a resistant 2009 H1N1 virus in the Newcastle, Australia, area from June through August of 2011, the report notes. The authors of the new study looked for signs of the resistant strain in Sydney, the nearest major city to Newcastle, 120 kilometers away. They ran genetic assessments of H1N1 viruses from 143 patients who had not received oseltamivr and from 23 patients who had been treated with it. Only 2 (1.4%) of the 143 isolates from untreated patients carried the resistance mutation (H275Y in the neuraminidase), indicating a low prevalence of the resistant strain and "no convincing evidence" of its spread from the Newcastle area. The resistance mutation was found in 3 (13%) of the 23 samples from treated patients, a significantly higher proportion, which is consistent with previous findings that resistance usually emerges in response to drug selection pressure, the authors say. They add that their findings show continued genetic evolution and antigenic drift in 2009 H1N1 viruses in Australia.