TOKYO (Reuters) - A genetic mutation of H1N1 swine flu that is resistant to the antiviral drug Tamiflu has been detected in a Japanese teenager who had not previously been treated with the drug, a Japanese health official said.
The case could mark Japan’s first instance of person-to-person transmission of a Tamiflu-resistant strain of the H1N1 flu but Health Ministry official Takeshi Enami said there was still insufficient evidence to confirm that.
“We cannot deny that this could be person-to-person transmission, but we are not able to reach that conclusion,” Enami said. Japan has had eight cases of new H1N1 patients who were resistant to Tamiflu, he added.
The Geneva-based World Health Organisation (WHO) said in late September that drug-resistant pandemic flu viruses had appeared infrequently and there was no evidence that they were spreading, but that further cases were likely.
The mutation was detected by health officials in Sapporo, northern Japan, in a teenage girl who had developed a fever on Aug. 22. She was given GlaxoSmithkline’s Relenza and recovered a day later, the ministry said in a statement.
The detected mutation did not worsen the virus, nor were there signs of an unusual rise in new H1N1 cases nearby, it said.
The risk of resistance is higher in patients who suffer from weak immune systems and have already been treated with Tamiflu, manufactured by Roche Holding under license from Gilead Sciences.
It is also high in people who are treated with antivirals as a precaution after exposure to someone with influenza but nevertheless develop the disease.
Reporting by Linda Sieg and Yoko Nishikawa; Editing by Rodney Joyce and Edwina Gibbs