Tamiflu-Resistant Swine Flu in U.S.?

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Drug-Resistant Swine Flu Seen in Teenage Traveler From San Francisco

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

July 7, 2009 -- Is Tamiflu-resistant swine flu spreading in the United States?

A 16-year-old girl traveling from San Francisco was found to be infected with Tamiflu-resistant swine flu after triggering a temperature-monitoring device in the Hong Kong airport. That has set off a West Coast search for others who might be carrying the drug-resistant virus.

So far, no other Tamiflu-resistant swine flu bugs have been detected in California or in Hong Kong. But unlike two previous, unrelated patients with Tamiflu-resistant swine flu -- one in Denmark, the other in Japan -- the girl from San Francisco had never been treated with Tamiflu.

"This strongly suggests transmission of Tamiflu-resistant virus to her," CDC flu expert Tim Uyeki, MD, tells WebMD. "How that actually happened, there is no way to know."

Swine flu already is resistant to the older generation of flu drugs. But so far, it remains sensitive to the two drugs known as neuraminidase inhibitors: Tamiflu and Relenza. Tamiflu is taken in pill form; Relenza must be inhaled.

"We do need to really monitor for the potential of a Tamiflu-resistant novel H1N1 strain to spread," Uyeki says. "If it does, this would be quite a concern because we have limited choices of antiviral medications. The good news is all of these Tamiflu-resistant strains are still sensitive to Relenza."

The girl's virus carried the same genetic change seen in the two previous cases from the widely separated patients in Denmark and in Japan. It's possible all three viruses arose from random mutation, says the World Health Organization's main flu expert, Keiji Fukuda, MD.

While any sign of drug resistance is a concern, it's reassuring that the novel H1N1 swine flu bugs have not swapped genetic elements -- recombined -- with the seasonal H1N1 flu bug. Seasonal H1N1 flu virus already is resistant to Tamiflu. Experts fear it may pass this and other undesirable traits to the swine flu bug via recombination.

"These resistant pandemic viruses are due to mutations, not to a mixture with current seasonal viruses resistant to Tamiflu," Fukuda said at a news conference. "So right now, they look like spontaneous mutations ... We do not see any evidence of widespread movement of Tamiflu-resistant viruses, including among close contacts of these persons."

Fukuda and Uyeki stress that there has been no change to current treatment recommendations. In the United States, the CDC recommends:

• Tamiflu treatment for people hospitalized with swine flu.
• Tamiflu treatment for swine flu patients at risk of serious flu complications due to underlying medical conditions.
• Tamiflu treatment for swine flu patients at risk of serious flu complications because they are pregnant, under age 5, or over age 65.
• Tamiflu to prevent infection of people at risk of serious flu complications who have been exposed to someone with swine flu.

SOURCES: Tim Uyeki, MD, medical epidemiologist, Influenza Branch, National Center for Infectious Diseases, CDC, Atlanta. Keiji Fukuda, MD, World Health Organization, assistant director-general ad. interim for Health Security and Environment, Geneva. CDC: "Interim Guidance on Antiviral Recommendations for Patients with Novel Influenza A (H1N1) Virus Infection and Their Close Contacts." News release, Hong Kong Department of Health.

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