First transmission of antiviral-resistant swine flu

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Researchers from the Centers for Disease Control and Prevention have identified what they believe to be the first case involving transmission of a Tamiflu-resistant pandemic H1N1 virus from one person to another but have so far found no evidence that the virus spread beyond the initial two known patients. But the findings highlight the dangers of using antiviral drugs like Tamiflu in an effort to prevent infections by the virus, commonly known as swine flu. Researchers fear that indiscriminate use of the drugs will lead to widespread resistance, as is now the case with seasonal flu, and the new findings provide the first hint that this could easily happen.

As of Sept. 4, the CDC has identified a total of nine cases of resistance to Tamiflu, known generically as oseltamivir. The drug’s manufacturer, Roche Holding, said Monday that it knows of 13 cases worldwide.

The new cases, reported today in the CDC’s Morbidity and Mortality Weekly Report, involve two girls who were attending summer camp in North Carolina. Both girls, who shared the same cabin, had been given Tamiflu prophylactically after an outbreak of pandemic H1N1 virus at the camp; at least 600 campers and staff were treated with the drugs. Despite their use of Tamiflu, both girls developed symptoms of flu and were subsequently confirmed to have the virus. The testing also showed that each girl’s virus was resistant to Tamiflu but not to Relenza, the other antiviral agent used to treat swine flu. Both were given therapeutic doses of Tamiflu and recovered with no problems.

Six other campers who received Tamiflu prophylactically also contracted swine flu, but their viruses were not tested for resistance. Researchers do not know whether the two girls developed the resistant virus independently -- unlikely -- or if they were both infected by a third, as-yet-unidentified camper. But the heartening news is that a study of their families showed that the virus was apparently not transmitted to anyone else by them.

-- Thomas H. Maugh II