Tamiflu Resistance in Northern California
Recombinomics Commentary 12:42
August 28, 2009

During this week, the CDPH Viral and Rickettsial Diseases Laboratory detected a specimen with the H275Y resistance mutation (associated with oseltamivir resistance); the result was confirmed by the CDC. This is the first time that this mutation has been detected by the VRDL and provides strong evidence for the importance of enhanced surveillance for antiviral resistance testing. The specimen was obtained from a hospitalized patient in Northern California.

The above comments are from the latest report from the California Department of Public Health and may be the first example of a hospitalized patient in the US who has H274Y and is not immuno-compromised.  Earlier two immuno-compromised cancer patients were described in Seattle, in addition to two summer campers in North Carolina who were on prophylactic Tamiflu

Earlier a traveler from San Francisco was H274Y positive in Hong Kong, and had no reported Tamiflu exposure, raising concerns of an evolutionarily fit pandemic H1N1 circulating in northern California, since the infected travel was symptomatic during or shortly after deplaning form a non-stop flight originating in San Francisco.

The above description does not include Tamiflu use in the hospitalized patient, so it is unclear if the H274Y was detected prior to treatment or if treatment selected for H274Y.  Prior cases developed resistance shortly after the start of treatment, raising concerns of H274Y circulation as minor component in worldwide infections, leading to increases in deaths as seen in California, or widespread outbreaks as seen in schools in the southern United States.

Moreover, the number of cases of resistance continues to rise.  The latest WHO update on reported cases cites four for Japan, indicating another patient on prophylactic Tamiflu developed an infection which was H274Y positive.

More information on Tamiflu exposure linked to the hospitalized patient in northern California, as well as sequence data on the growing number of H274Y positive cases would be useful.

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