Influenza Update

WHO responds to reports of patient-to-patient spread of Tamiflu-resistant H1N1 virus

Media reports in November noted that Tamiflu resistant swine flu had spread between patients in a hospital ward. The BBC reported that “a total of five patients on a unit treating people with severe underlying health conditions at the University Hospital of Wales, Cardiff were infected. Of those, three appear to have acquired the infection in hospital.

“They are thought to be the first confirmed cases of person-to-person transmission of a Tamiflu-resistant strain in the world. There have been several dozen reports around the world of people developing resistance to Tamiflu while taking the drug, but they have not passed on the strain to others.”

In a media briefing on 26 November Dr Keiji Fukuda, Special Adviser to the Director-General on Pandemic Influenza, World Health Organisation, responded to these reports.

“There have been two separate clusters of oseltamivir resistance identified in the UK and in the United States. In the United Kingdom there were nine patients in a hospital who developed pandemic illness and from five of these patients, oseltamivir resistant viruses were identified,” Dr Fukuda said.

“In a separate cluster in the United States there were four patients in one hospital who also developed pandemic illness while hospitalised.”

According to the WHO, all the resistant viruses carried the same H275Y mutation, indicating resistance to oseltamivir, but susceptibility to the second antiviral drug, zanamivir.

Dr Fukuda said these people were in immuno-compromised conditions either because of their underlying disease – some of which were hematologic malignancies – or because of treatment for their disease.

In a statement issued 2 December, the WHO said 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.

The WHO added the outbreaks are being further investigated to determine the mode of transmission within the wards. No illness in staff caring for these patients has been detected.


The WHO pointed out that once oseltamivir resistant virus has been detected in a ward treating severely immunocompromised patients, doctors should consider switching to zanamivir as the antiviral drug of first choice for treatment, and when considering post exposure prophylactic treatment of other patients on the ward.

ate of upload: 26th Jan 2010

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