Health researchers say most flu viruses circulating in America this winter are resistant to two commonly used prescription drugs. So far, the antiviral drug Tamiflu still works to fight flu viruses — but experts warn that could change if Tamiflu becomes too widely available, and viruses develop strains resistant to the drug.
MADELEINE BRAND, host: I'm Madeline Brand and this is Day to Day. The flu virus continues to surprise scientists. A new online report in the Journal of the American Medical Association says nearly all the flu viruses infecting Americans this winter are resistant to two of the four anti-flu drugs on the market. NPR's Richard Knox reports.</s>RICHARD KNOX, reporting: Scientists at the Centers for Disease Control and Prevention admit they were caught off-guard by the rapid spread of drug resistant flu.</s>Mr. RICK BRIGHT (Centers for Disease Control): We've never seen resistance on this level anywhere in the world for an anti-viral drug for influenza.</s>RICHARD KNOX, reporting: Rick Bright of the CDC has been watching the spread of flu viruses resistant to the drugs amantadine and ramantadine.</s>Mr. RICK BRIGHT (Centers for Disease Control): We anticipated that the rate would continue to rise in the United States over the next few years, but when we found a 91 or 92 percent rate of resistance in the United States this year it was very shocking how quickly those viruses spread to our country.</s>RICHARD KNOX, reporting: The resistant flu viruses probably came from China or Russia. That's because people there can buy non-prescription cold and flu remedies containing amantadine and ramantadine. They've probably been buying more of those remedies lately because of all the alarm about bird flu. The more flu viruses are exposed to these drugs the more they're going to develop the genetic mutations that make them drug resistant. Now the CDC is urging doctors to stop using the drugs. That doesn't affect most Americans with the flu, but Dr. Marci Layton of the New York City Health Department says it's a problem for people in nursing homes, for example.</s>Dr. MARCI LAYTON (New York City Health Department): As soon as we recognize any suggestion of a flu outbreak in any long term care facility where the patients are at high risk, our recommendation to the medical director is to start anti-virals as soon as possible and to be liberal in who you target it to.</s>RICHARD KNOX, reporting: Hospitalized children also get these drugs when flu invades pediatric wards. Now health care facilities have to switch to an anti-flu drug called Tamiflu.</s>Dr. MARCI LAYTON (New York City Health Department): The fact that now they need to use Tamiflu which is more expensive has made it difficult, but that's what we're recommending.</s>RICHARD KNOX, reporting: Dr. David Weinstock is an infectious disease specialist at Memorial Sloan-Kettering Cancer Center in New York. He says the bigger lesson is how fast resistant flu viruses can span the planet.</s>Dr. DAVID WEINSTOCK (Infectious Disease Specialist, Memorial Sloan-Kettering Cancer Center): Influenza connects us to the rest of the world in ways that many other infections don't. You know, your average pneumonia is caused by a bacteria that you get from a person who is near you, but it's very distant from that same type of bacteria in China, for example. On the other hand, influenza, the organism that develops there only a few months ago could be the organism that person in America is infected with.</s>RICHARD KNOX, reporting: Now Tamiflu is the flu drug of choice. People all over the world are clamoring for it, but if they start taking it at the first sign of a cold or fever researchers wonder if flu viruses will become resistant to Tamiflu.</s>Dr. DAVID WEINSTOCK (Infectious Disease Specialist, Memorial Sloan-Kettering Cancer Center): We don't know the answer to that, but we think that if that is the case it's going to be a slow evolution, as opposed to the very rapid evolution that we've seen with amantadine and ramantadine and that's because mutations in influenza that make it resistant to drugs like Tamiflu seem also to make it into a weaker organism.</s>RICHARD KNOX, reporting: On the other hand, experts are worried about signs that the bird flu, spreading from Asia to the Middle East, can become resistant to Tamiflu. If that trend accelerates that would leave the world with virtually no treatment option against bird flu. Richard Knox, NPR News.