HPA statement on possible transmission
20 November 2009
The HPA is working with colleagues from the Public Health Service of Wales to investigate a number of possible cases of person to person transmission of oseltamivir resistant swine flu.
To date, a total of nine H1N1v confirmed cases have been reported amongst patients on a hospital ward in Wales. Five of these cases are known to be resistant to oseltamivir, one is sensitive and for three resistance status is presently unknown.
The virus has emerged in a group of particularly vulnerable individuals in whom the development of oseltamivir resistance is well documented. At present we believe the risk to the general healthy population is low. There is no evidence that the oseltamivir resistant virus is any more virulent than any other type of flu. The situation is being kept under review.
Further follow-up of cases and their close contacts both on the ward and in the community is underway to ascertain if there is evidence of onward transmission. The virus remains sensitive to the other frontline drug Relenza® which is being used as an alternative antiviral and patients are responding well.
Although further epidemiological investigation is underway, it would seem likely that transmission of oseltamivir-resistant H1N1 virus has taken place.
The current cases of oseltamivir resistance under investigation have all occurred in patients with haematological problems which result in immuno-suppression either because of the disorder or the chemotherapy given to treat the disorder.
Oseltamivir resistance to influenza viruses is well documented in immunosuppressed individuals and can develop quickly. It is likely to be associated with the high viral load which may occur during infection in these patients.
In addition, immunosuppressed people may be more susceptible to infection ie a smaller exposure may result in infection in these patients.
Antiviral resistance monitoring has been in place in the UK for a number of years and this allows us to identify drug resistance early so that cases can be investigated and managed appropriately
It still remains appropriate to use oseltamivir for the treatment and prophylaxis of influenza in the UK. Guidance is being developed to cover the particular instance where modifications to the current antiviral treatment policy may be required.
Background information
As of 20th November, WHO have reported 57 incidences of oseltamivir resistance worldwide.
There have been no documented episodes of person to person transmission of a oseltamivir resistant pandemic influenza virus. A small number of individual cases have been identified, however, in whom drug resistant virus has been isolated with no history of prior use of anti-virals..
In addition, on 19 November, WHO was notified by the US of four patients with infection with oseltamivir-resistant pandemic H1N1 2009 influenza virus among inpatients in the same unit at a hospital during October and November. The possibility that these viruses have been transmitted within this hospital unit is currently under investigation.
Generally, the pandemic H1N1 oseltamivir resistant viruses are not considered "fit" and transmission is poor.
Ends
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Last reviewed: 20 November 2009
