# 3526
No one really knows the true extent of oseltamivir (Tamiflu) resistance among the millions of cases of swine flu circulating around the world. It is thought to still be small, but it is also suspected to be growing.
Genetic testing for the known (and there could be other) mutations that can cause resistance are done to only a very small percentage of actual flu cases.
In the United States, as of last Friday, the CDC had reported testing 267 isolates – none of which showed resistance to the antiviral drug. Worldwide, more than 1,000 isolates have been tested.
And of those, we are told fewer than a half dozen have shown resistance.
Nevertheless, Tamiflu resistance appeared suddenly and spread quickly in 2008 in the H1N1 seasonal flu virus. And the fear is that the same thing will happen with the novel H1N1 virus.
Canada has reported their first documented case of resistance, and Japan has now reported a second instance. There have been other suspected cases of resistance reported in the media, but not all of them have been confirmed.
For now, Tamiflu remains effective as a treatment (but not a cure) for most cases of the novel H1N1 virus. If administered early enough in the infection, it can reduce the severity and duration of symptoms.
Helen Branswell brings us up to date with the latest cases.
Tamiflu-resistant swine flu case in Quebec
By Helen Branswell, THE CANADIAN PRESS
Last Updated: 22nd July 2009, 9:30am
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.
