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The Indiana State Department of Health (ISDH) is alerting health care providers about oseltamivir resistance of the currently circulating influenza A (H1N1) virus.

Providers are strongly encouraged to submit specimens to the ISDH Laboratory for surveillance testing and should contact Katie Masterson at kmasterson@isdh.in.gov or 317-921-5843. The influenza specimen submission form is available on the ISDH web site located at http://www.in.gov/icpr/webfile/formsdiv/35212.pdf. Facilities are invited to participate in influenza sentinel surveillance and should contact Shawn Richards at srichard@isdh.in.gov or 317-233-7125.

CDC published an Influenza Update in the MMWR on Friday, December 12, 2008 describing these preliminary data. The entire document is located at http://www.cdc.gov/mmwr/. Highlights of the document include:

• Oseltamivir-resistant influenza A (H1N1) viruses have been detected for the 2008-09 season. Preliminary CDC data show that that 24 of the 25 influenza A (H1N1) viruses tested in two states (not including Indiana) were resistant to oseltamivir. All H1N1 viruses were sensitive to zanamivir.
• The influenza A (H1N1) viruses found to be oseltamivir-resistant are antigenically similar to the components included in the 2008-09 vaccine.
• All five influenza A (H3N2) and nine influenza B viruses tested were sensitive to oseltamivir and zanamivir.
• Twenty-five influenza A (H1N1) and five influenza A (H3N2) viruses were tested for adamantane resistance.  All influenza A (H1N1) viruses were sensitive to adamantanes, and all influenza A (H3N2) viruses tested were resistant to adamantanes. The adamantanes are not effective against influenza B viruses.
• CDC has antigenically characterized 30 influenza viruses collected by U.S. laboratories during the 2008-09 season, including 20 influenza A (H1N1), three influenza A (H3N2), and seven influenza B viruses. Twenty-seven of the 30 viruses were antigenically related to the components included in the 2008-09 influenza vaccine (A/Brisbane/59/2007-like (H1N1), A/Brisbane/10/2007-like (H3N2), and B/Florida/04/2006-like). The other three influenza B viruses belong to the  B/Victoria/02/87 lineage.
• No influenza-associated pediatric hospitalizations have yet been reported.
• Clinicians should remain alert for changes in recommendations that might occur as the 2008-09 influenza season progresses.

Recommendations regarding the use of antiviral medications might be revised if surveillance data indicate a substantial and widespread increase in the prevalence of oseltamivir-resistant influenza viruses in the United States.

Alternatives for antiviral treatment in the setting of widely circulating oseltamivir-resistant viruses have been suggested. These treatment options, which might include preferential use of zanamivir or therapy with a combination of antivirals for certain patients, have been outlined in the ACIP 2008 influenza recommendations.  Currently, the neuraminidase inhibitors oseltamivir and zanamivir remain the recommended medications for treatment and chemoprophylaxis of influenza.

Vaccination remains the cornerstone of influenza prevention efforts. Influenza vaccination can prevent influenza infections from strains that are sensitive or resistant to antiviral medications.

CDC continues to conduct surveillance to provide up-to-date recommendations regarding prevention and treatment of influenza. Influenza surveillance reports for the United States are posted online weekly during October-May and are available at http://www.cdc.gov/flu/weekly/fluactivity.htm.  Additional information regarding influenza viruses, influenza surveillance, influenza vaccine, and avian influenza is available at http://www.cdc.gov/flu.