TORONTO – Canada has recorded a case of Tamiflu-resistant swine flu virus, in a Quebec man who had been given the drug to prevent infection.
Meanwhile, Japan revealed Tuesday it had found a second such case of Tamiflu resistance, in a person who has no ties to the country’s earlier reported case.
The cases are the fourth and fifth globally since the new H1N1 virus was discovered in April.
The Quebec man, 60, was given the flu antiviral after his son fell ill with the pandemic virus. It’s believed the resistance arose in the man and there is no evidence he transmitted resistant virus to anyone else.
“It appears to be an isolated case,” said Jirina Vlk, spokesperson for the Public Health Agency of Canada.
“Although the strain does not appear to have spread beyond the reported individual case we continue to be vigilant on this front.”
Use of Tamiflu to prevent infection – a procedure called prophylaxis – has been seen on occasion to give rise to resistant viruses.
“We know that it was going to happen and it’s not good news that it’s happening,” said Dr. Allison McGeer, an influenza expert at Toronto’s Mount Sinai Hospital.
But she said given the amount of Tamiflu being used in the world right now, such cases are bound to arise.
“It’s the problem with influenza, right? Either we’re going to see small numbers of these and they’re just going to kind of appear periodically and we’re all going to worry or it’s going to go big,” McGeer said.
“There’s probably not going to be much in between.”
Another such case cropped up in Japan, in the city of Yamaguchi. Japan’s National Institute of Infectious Diseases logged genetic sequence data for the virus on Tuesday in Genbank, a repository for genetic sequences used by flu researchers.
The lab’s director, Dr. Masato Tashiro, confirmed the case in an email containing details provided to the World Health Organization.
The new case was a person who had been given the antiviral drug as post-exposure prophylaxis – an attempt to prevent illness in a person exposed to the pandemic virus.
The person has since recovered, and it appears that there has been no spread, the email stated. The virus was sensitive to Relenza, a second drug in the same class as Tamiflu.
The earlier Japanese case had occurred in a person in the city of Osaka.
Other cases have been reported by Denmark and Hong Kong. Four of the five cases arose in people who had been taking the drug.
One, however, was recorded in a girl from San Francisco who travelled while sick to Hong Kong. Health inspectors at the airport there pulled her aside and tested her for swine flu.
She was positive, but told doctors there she hadn’t taken Tamiflu. That suggests the virus that caused her infection was already resistant. U.S. officials have intensified surveillance for resistant viruses in the San Francisco area but say they have not found other cases.
The Public Health Agency says the Quebec man recovered from his bout of swine flu without complications and never needed hospitalization.
Vlk said the agency recommends using Tamiflu for treatment only, adding prudent use of the drug could stave off the development of resistance.
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