Chinese doctors report they've seen signs that the bird flu virus infecting humans is able to overcome one of the few drugs used to fight it.

In a report published online Tuesday by The Lancet, doctors report on 14 patients infected with the H7N9 virus and admitted to the Shanghai Public Health Clinical Center in April. All the people came down with pneumonia, and two died.

As part of treatment, all the patients were given the antiviral drug , or oseltamivir. The doctors took regular samples from the hospitalized patients to see how much of the virus was in their bodies as time went on.

The good news is that that the number of viral particles in their bodies (the so-called viral load) decreased in most of the patients treated with Tamiflu. And as the viral load fell, the patients began to get well.

Also, the viral load remained high during the first week after infection, which the doctors say would suggest that treatment with Tamiflu be helpful even after the first few days of illness have passed. For run-of-the-mill flu, Tamiflu is supposed to be started no later than two days after infection.

So the doctors concluded that early treatment of bird flu cases with Tamiflu makes sense and should be "strongly encouraged."

Now the bad news. The virus that infected two of the patients who also got steroids to ease their symptoms developed a genetic mutation that's known to confer resistance to Tamiflu. The patients' viral load got heavier — rebounding after treatment — and the patients got worse.

It's not clear if the steroids played a role in the development of resistance or that was a coincidence.

"The emergence of antiviral resistance in [avian]/H7N9 viruses, especially in patients receiving corticosteroid therapy, is concerning, needs to be closely monitored, and considered in pandemic preparedness planning," the authors of the paper conclude.

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