A report in the Journal of the American Medical Association (JAMA) found that the H1N1 subtype of influenza A viruses commonly proved resistant to the popular drug oseltamivir.

Oseltamivir, sold commercially in the United States as the drug Tamiflu, is produced by Swiss pharmaceutical giant Roche, and is the main antiviral remedy on the market.

But during the 2007-2008 flu season last year, the Tamiflu-resistant strain of the virus accounted for fully one in five cases of flu in the United States.

Preliminary data during the current 2008-2009 influenza season shows that the virus's resistance to the Tamiflu continues to be high and that the drug-resistant strain of the flu continue to have a high incidence.

Equally worrying is the virulence of this particular strain of flu. Data last year for 99 individuals infected with oseltamivir-resistant influenza found that five of the patients had to be hospitalized, four of whom died.

The authors wrote that the worrisome development "has highlighted the need for the development of new antiviral drugs and rapid diagnostic tests that determine viral subtype or resistance."

In an editorial accompanying the study, David Weinstock of the Dana-Farber Cancer Institute, Boston, and Gianna Zuccotti of Boston's Brigham and Women's Hospital said that the findings also show that researcher can never become complacent when treating the scourge.

"New surprises await in the perpetual struggle with influenza," they wrote.

"One thing is certain -- the organism will continue to evolve."

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