CDC Warns of Drug-Resistant Flu Bug

Dec. 19, 2008 -- A flu strain now spreading in the U.S. is resistant to the flu drug Tamiflu, the CDC today warned in an official health advisory to doctors.

Flu is a dangerous and sometimes deadly disease. But the Tamiflu-resistant strain isn't any more or less dangerous than other flu strains.

The Tamiflu-resistant virus is the flu bug most commonly seen so far this year. It's been detected in 12 states so far, mostly in Hawaii and Texas.

Tamiflu resistance wasn't unexpected. What was surprising was the rapid rise of Tamiflu resistance in this particular flu bug. Last year, about 11% of type A H1N1 flu bugs were resistant. So far this year, 49 out of 50 H1N1 viruses have been resistant.

Even so, it's still very early in the flu season. There's no way to know whether the Tamiflu-resistant flu bug will be this year's predominant cause of flu.

"There is no crystal ball here," CDC Director Julie Gerberding, MD, tells WebMD. "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."

Three different flu bugs are in circulation among humans. The resistant bug is the type A H1N1 strain. There's also the type A H3N2 strain, and one type B strain.

The current flu vaccine protects against all three of these viruses -- and the current flu vaccine is an excellent match for the drug-resistant bug, Gerberding says.

Fortunately, the Tamiflu-resistant flu bug is still sensitive to Relenza, an alternative flu drug of the same basic type as Tamiflu. And the bug may also be sensitive to the older flu drugs Flumadine and Symmetrel, although resistance to these drugs has been steadily increasing among type A flu bugs.

Flu drugs can be used both to treat and to prevent the flu:

• Treatment with flu drugs must begin no later than two days after symptoms appear. The earlier that treatment begins, the shorter and less severe the illness.
• Prevention with flu drugs is used in households, hospitals, or facilities (such as nursing homes) where people have been exposed to someone who has the flu.

Tamiflu 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.

Relenza comes in an inhaler. Children younger than 7 can't use it 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.

Ironically, the CDC's Tamiflu warning is not going to make a huge difference in how patients are treated because too few people get treated with flu drugs, says Joseph S. Bresee, MD, chief of the epidemiology and prevention branch of the CDC's flu division.