Pandemic (H1N1) 2009 briefing note 18
Oseltamivir resistance in immunocompromised hospital patients

2 DECEMBER 2009 | GENEVA — WHO has been informed of two recent clusters of patients infected with oseltamivir-resistant H1N1 viruses. Both clusters, detected in Wales, UK and North Carolina, USA, occurred in a single ward in a hospital, and both involved patients whose immune systems were severely compromised or suppressed. Transmission of resistant virus from one patient to another is suspected in both outbreaks.

The emergence of drug-resistant influenza viruses in severely immunosuppressed or immunocompromised patients undergoing antiviral treatment is not unexpected and has been well documented during seasonal influenza. Virus replication can persist in such patients for prolonged periods of time despite antiviral treatment, creating an environment in which drug-resistant viruses can readily be selected. This phenomenon has also been observed for the pandemic (H1N1) 2009.

Upon receipt of the reports, WHO organized a telephone conference with officials and staff from the hospitals and experts in clinical medicine, epidemiology, and virology to discuss the two outbreaks. Particular attention is being given to the best treatment options for immunocompromised patients who become infected with the pandemic virus.

http://www.who.int/csr/disease/swineflu/notes/briefing_20091202/en/index.html