Oseltamivir-resistant novel influenza A(H1N1) virus infection has been identified in the United States for the first time, in two severely immunosuppressed patients treated for leukemia in Seattle hospitals.
The teenaged male and a woman in her 40s had undergone hematopoietic stem cell transplants. Both were initially infected with oseltamivir-susceptible viruses that later developed resistance. The two patients were not linked epidemiologically. There was no evidence of transmission of the oseltamivir-resistant virus to health care providers, the Centers for Disease Control and Prevention reported.
In both patients, the viruses were susceptible to zanamivir. Sequence analysis showed that the oseltamivir resistance was not the result of gene reassortment with seasonal influenza A(H1N1) virus.
Immunosuppressed patients should receive annual influenza vaccination. Clinicians caring for immunosuppressed patients infected with novel H1N1 should be aware of the potential for antiviral drug resistance and prolonged viral shedding, the CDC said.
The public health risk of virus transmission from these two cases appears to be low. Washington state, working with the CDC, is conducting enhanced surveillance for oseltamivir resistance among novel H1N1 virus strains.
Oseltamivir or zanamivir are recommended for all hospitalized patients with suspected or confirmed novel H1N1 and for outpatients at increased risk for influenza-related complications.
For guidance on treating and preventing novel H1N1, go to www.cdc.gov/h1n1flu