December 23, 2009
Flu Bulletin #18
Manitoba Health is reporting a case of oseltamivir (antiviral) resistance in a child under the age of 18 who was being treated for lab-confirmed H1N1. The child has an underlying medical condition and was not hospitalized.
A public health investigation continues, but it appears this is an isolated case with no evidence to date that a resistant strain of H1N1 flu has been transmitted to others.
At this time, Manitoba Health is not recommending any changes to its clinical care guidelines on the appropriate use of antivirals for H1N1 flu. Information about antiviral use and this case is being sent to health-care providers. In addition, Manitoba Health continues to recommend that Manitobans take the same basic precautions to prevent infection, including getting the H1N1 flu shot, and follow previous advice on when to seek care for their symptoms.
This case was found as part of routine testing of influenza specimens for antiviral resistance at the Public Health Agency of Canada’s National Microbiology Lab in Winnipeg.
Oseltamivir (Tamiflu) is an antiviral drug commonly used to treat people infected with influenza. This is the first case of antiviral resistance related to H1N1 flu reported in Manitoba and the eighth in Canada. Other cases are being reported around the world and have also been noted in some clinical drug trials. These antiviral resistant cases appear to be isolated as there have been no reports showing evidence of transmission to others. This is being monitored by the World Health Organization.
Antiviral resistance has previously been found with some strains of seasonal flu. It occurs when there is a shift or mutation of the flu virus into a resistant strain. It can be difficult to pinpoint the cause in a single case, but generally antiviral resistance can result when:
· people don’t finish the antivirals prescribed to them to treat an illness or don’t follow the directions for their use;
· antivirals are prescribed to prevent rather than treat illness;
· prolonged treatment with antivirals is prescribed, particularly for people with weakened immune systems; or
· the virus imperfectly replicates itself, creating genetic changes that make antivirals less effective.
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