Two locally-treated patients infected with Tamiflu-resistant H1N1 virus (swine flu)

KING COUNTY, WA - In a report that is planned for publication today in the federal Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report Dispatch, two immunosuppressed patients being treated for H1N1 (swine flu) influenza in King County have been identified as resistant to oseltamivir, commonly known by the brand name Tamiflu, an antiviral treatment used for the infection.

"Viruses can develop drug resistance over time. It's important that antiviral treatments only be used as recommended by a health care provider, to minimize drug resistance and preserve an important tool against the illness for those who need it," said Dr. David Fleming, Director and Health Officer for Public Health - Seattle & King County. "The vast majority of people with H1N1 virus continue to be treatable with Tamiflu, and in cases where it becomes ineffective, other options are available."

Currently, antiviral drug treatment for H1N1 virus infections with oseltamivir or zanamivir (Relenza) is recommended for hospitalized persons who are ill with influenza and outpatients who are at high risk of complications, including young children, pregnant women, and persons with chronic medical conditions such as lung disease, asthma, heart disease and diabetes. No changes in antiviral treatment recommendations have been made as a result of these two cases.

The two patients, one a male teenager and the other a female in her 40's, had no links to one another and these infections are not believed to be related. Both patients had compromised immune systems, a condition that has previously been shown to raise the risk for prolonged seasonal influenza virus infection and development of antiviral resistance during treatment. One patient is currently no longer ill from the influenza virus infection and the other has ongoing symptoms and is being treated with the antiviral medication zanamivir. More details about the cases will be found in the MMWR Dispatch at www.cdc.gov/mmwr.

There is no evidence that health care workers or other contacts of these two people became infected with a Tamiflu-resistant virus. The risk of infection to the general population is very low from these cases, but as a precaution, local and state health officials are working in collaboration with the CDC to conduct enhanced monitoring for antiviral drug resistant influenza in the community.

As of August 11, 2009, a total of 11 novel H1N1 influenza viruses that are resistant to Tamiflu have been reported worldwide.

A vaccine for the H1N1 virus is being developed rapidly in anticipation of a resurgence of the H1N1 virus in the United States this fall. Locally, Public Health is preparing to distribute vaccine in the most effective way to those recommended to receive it as it becomes available. Federal officials are reporting that current plans are to begin delivering vaccine in October.

Check Public Health's website for frequently updated information and resources: www.kingcounty.gov/health/H1N1.