The Centers for Disease Control (CDC) warned in an official health advisory to doctors that the most common flu bug that is spreading in the U. S. is resistant to the flu drug Tamiflu.

The Tamiflu-resistant virus is the flu bug most commonly seen so far this year and has been detected in 12 states so far, mostly in Hawaii and Texas. The strain is not more or less dangerous than other flu strains.

Medical experts say Tamiflu resistance was not unexpected though the speed of Tamiflu resistance was surprising. Last year 11 % of type A H1N1 flu bugs were resistant while this year, 49 out of 50 H1N1 viruses have been resistant.

CDC Director Julie Gerberding, MD said, "There is no crystal ball here. We can't predict if this strain will end up being the most important one this year. It could fizzle out. ... We're giving a 'heads-up' to the clinicians, but we are not making drastic changes in our treatment and prevention recommendations."

There are no ways of knowing this early in the flu season if Tamiflu resistant flu bug will be this year's predominant cause of the flu. In humans three different flu bugs are in circulation, with type A H3N2 strain, one type B strain and the resistant bug is the type A H1N1 strain. Gerberding said the current flu vaccine protects against all three of the virus and is an excellent match for the drug resistant bug.

Tamiflu which can run $100 a box, has been the most attractive treatment because it is taken in pill form and can be given to children as young as 1 year old. There are alternatives for the flu such as Relenza, which the Tamiflu-resistant flu bug is still sensitive to as well as older drugs such as Flumadine and Symmetrel, although resistance to these drugs has been steadily increasing among type A flu bugs.

Relenza which comes in an inhaler cannot be used for children younger than 7 for treatment, and those younger than 5 can't use it for prevention. Moreover, Relenza sometimes causes lung spasms, so it can't be used by people with lung problems.

Joseph S. Bresee, MD, chief of the epidemiology and prevention branch of the CDC's flu division said, "Even among hospital patients with the flu, more than half do not receive antiviral therapy. Tamiflu] and [Relenza] are relatively underused at this point."

He said that the current warning may actually see an increase in the use of flu drugs by increasing awareness in doctors on how to use them.