Tamiflu resistance to A/H1N1 swine flu has been formally reported by the World Health Organization (WHO) in Hunan, China and Singapore adding to the three cases in Japan, two in Hong Kong (the second just reported today) and one each in Denmark and Canada. There have also been media reports of some resistance in Thailand, but it is unclear how many cases were found and if they were even confirmed. Resistance first reported along the Texas / Mexican border was later denied.
The Japanese, Danish, Canadian and second Hong Kong patients all had been taking Tamiflu as a preventive measure after exposure to the disease and still developed symptoms of flu around the fifth day of their prophylactic treatment, suggesting development of resistant strains after taking the drug.
The first Hong Kong case involved a 16 year old American teen flying from San Francisco who had not taken Tamiflu before she became ill. The patient seen in Singapore was a 28 year old American woman flying from Hawaii. Although the details are not clear, it is possible that she too already had contracted a circulating resistant strain of the virus prior to treatment.
Lack of details from WHO has fostered concerns that Tamiflu resistance may be more widespread than officially reported. Speaking to the Canadian Press, Dr. Charles Penn, a scientist with WHO said that “reported cases to date have been isolated, with no connections among them and no sign that the infected people passed resistant viruses to their contacts.”
Tamiflu and Relenza are currently the only two antiviral drugs available to treat swine flu. Since its emergence in April, the now pandemic A/H1N1 swine flu virus has been resistant to two older antivirals, amantadine and rimantadine.
Dr. Penn stated that laboratories around the world are monitoring the virus, looking for changes in the strain that might suggest a similar problem of resistance.
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