Tamiflu-resistant Influenza Strains

(Update, 30 April 2009: I see from the server logs that this post is getting a lot of traffic today.  Please note that the contents of the post discuss the annual influenza strains in the US, not the "H1N1 Influenza A" strain, which at this time is susceptible to Tamiflu.)

The IHT is carrying a great article by Donald Mcneil on the sudden emergence of antiviral resistance in this year's circulating influenza viruses.  The title says it all: "Flu in U.S. found resistant to main antiviral drug".

Virtually all the flu in the United States this season is resistant to the leading antiviral drug Tamiflu...  The problem is not yet a public health crisis because this has been a below-average flu season so far and the chief strain circulating is still susceptible to other drugs.

There are two important points in this story.  First, the resistance seems to derive from a spontaneous mutation rather than having emerged from overuse of the drug:

"It's quite shocking," said Dr. Kent Sepkowitz, director of infection control at Memorial Sloan-Kettering Cancer Center in New York. "We've never lost an antimicrobial this fast. It blew me away."

The mutation appears to have arisen in Norway, a country that the article suggests does not even use Tamiflu. Second, while the CDC is recommending that hospitals test all flu cases to find out whether patients are carrying a the resistant subtype, this capability is still not widespread:

"We're a fancy hospital, and we can't even do the ... test in a timely fashion," Sepkowitz said. "I have no idea what a doctor in an unfancy office without that lab backup can do."

I haven't written very much about the flu for a couple of years, but it is clear that the threat is still quite present.

The article ends with this bit of speculation:

And while seasonal flu is relatively mild, the Tamiflu resistance could transfer onto the H5N1 bird flu circulating in Asia and Egypt, which has killed millions of birds and about 250 people since 2003. Although H5N1 has not turned into a pandemic strain, as many experts recently feared it would, it still could -- and Tamiflu resistance in that case would be a disaster.

I'm not so sure that the resistance gene "could easily transfer onto the H5N1 bird flu".  It sounds like Mr. Mcneil may be giving more weight here to Henry Niman (who is quoted extensively in the article on other specific topics) than the rest of the community might.  This is not to say that such a transfer is unlikely -- this is the sort of thing that I fear we know so little about that we could make poor assumptions leading to even worse policy.  The mechanisms for recombination and reassortment of genes in the flu are still disputed in the literature.  But it's damn scary, either way, even if the probability of such a transfer is small.

In the end, if nothing else, what this demonstrates is that our technological base for both detecting and responding to infectious disease is still poorly developed.