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Tamiflu Resistant Swine H1N1 in Hong Kong and San Francisco
Recombinomics Commentary 13:36
July 3, 2009

The virus was identified during PHLSB's routine sensitivity test of HSI virus to oseltamivir and zanamivir, the spokesman said.

"This is the first time Tamiflu resistance in HSI virus found in Hong Kong," he said, adding that similar cases were also reported in Denmark and possibly Japan.

"Tests showed that this strain is sensitive to zanamivir (Relenza)," he said.

The virus was isolated from the specimen taken from a 16-year-old girl coming from San Francisco. She was intercepted by Port Health Office at the Hong Kong International Airport on June 11 upon arrival. The girl was then admitted to Queen Mary Hospital for isolation. She was tested positive to HSI but opted not to take tamiflu. She had mild symptoms and was eventually discharged upon recovery on June 18.

The spokesman noted that PHLSB conducted routine sensitivity tests on specimens taken from confirmed HSI patients.

The above comments from the Hong Kong Department of Health press release describe Tamiflu resistance (presumably H274Y, aka H275Y) in a patient arriving from San Francisco.  The resistance was discovered during routine surveillance and there is no indication the patient was taking oseltamivir, indicating the pandemic H1N1 was evolutionarily fit.

The two other cases described this were (in Denmark and Japan) were in patients under prophylactic treat of Tamiflu.  In both cases the resistance was due to H274Y (and discovered because of the prophylactic treatment).

Evolutionarily fit swine flu with H274Y is cause for concern.  Last year seasonal H1N1 with H274Y spread worldwide.  It had previous spread from one genetic background to another via genetic hitchhiking and recombination.

It is likely that H274Y in pandemic H1N1 will now follow a similar, but accelerated, pathway due to widespread use of oseltamivir to control the spread of pandemic H1N1.

The export of H274Y from San Francisco, and failure to identify the polymorphism in the United States, raises serious surveillance concerns.

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