In recent years, because of rising concern about the potential for a flu pandemic, governments around the world have been stockpiling millions of doses of Tamiflu, along with smaller amounts of Relenza and older antivirals, amantadine and rimantadine.

Tamiflu still is effective against bird flu in most cases, though some variants show signs of reduced sensitivity, says Frederick Hayden of the Infectious Disease Society of America’s Pandemic Flu Task Force. “It’s important that we monitor susceptibility patterns, not only in humans but also in avian viruses.”

Meanwhile, for doctors treating patients with regular flu, this season has been dizzyingly complicated. Type A H1N1 flu, the predominant strain circulating now, is the one resistant to Tamiflu; the two others in circulation, type A H3N2 and type B, are not.

Patients who have H1N1 flu can be treated with Relenza if they can inhale the medicine. If not, they can take amantadine or rimantadine. But if they have either of the other two flu strains, they can take only Tamiflu or Relenza, because H3N2 flu is resistant to amantadine and rimantadine, and those drugs don’t work against type B flu.

The trouble is, most doctors don’t know which flu strain is infecting their patients. The symptoms are the same. Rapid flu diagnostic tests may be able to tell if it’s influenza A or B, but can’t identify type A subtypes, such as H1N1 or H3N2. The gold-standard test, a viral culture, takes about a week to produce results.

Source:  USATODAY.com

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