Major Flu Strain Found Resistant to Leading Drug

Virtually all the dominant strain of flu in the United States this season is resistant to the leading antiviral drug Tamiflu, and scientists and health officials are trying to figure out why. The problem is not yet a public health crisis because this has been a below-average flu season so far, and because the Tamiflu-resistant strain, one of three circulating, is still susceptible to other drugs. But infectious disease specialists are worried nonetheless. Last winter, about 11 percent of the throat swabs from patients with the most common type of flu that were sent to the Centers for Disease Control and Prevention for genetic typing showed a Tamiflu-resistant strain. This season, 99 percent do. “It’s quite shocking,” said Dr. Kent A. Sepkowitz, director of infection control at Memorial Sloan-Kettering Cancer Center in New York. “We’ve never lost an antimicrobial this fast. It blew me away.” The single mutation that creates Tamiflu resistance appears to be spontaneous, and not a reaction to overuse of the drug. It may have occurred in Asia, and it was widespread in Europe last year. In response, the disease control agency issued new guidelines two weeks ago. They urged doctors to test suspected flu cases as quickly as possible to see if they are influenza A or influenza B, and if they are A, whether they are H1 or H3 viruses. The only Tamiflu-resistant strain is an H1N1.