# 5815
Roughly 10 days ago, in Australia Reports Cluster Of Antiviral Resistant H1N1, I wrote of a large clustering of oseltamivir (Tamiflu) resistant H1N1 cases in New South Wales. More than 2 dozen patients – roughly 14% of the isolates tested from that region since May – have shown a genetic mutation that confers resistance.
Ever since the novel H1N1 swine flu virus appeared in the spring of 2009, scientists have worried that it would someday develop resistance to oseltamivir as its predecessor - seasonal H1N1 - did in 2008.
Overall, however, the news has been encouraging.
During the first two years, only 1%-2% of samples tested have shown the most common mutation known to convey oseltamivir resistance; H275Y, where a single amino acid substitution (histidine (H) to tyrosine (Y)) occurs at the neuraminidase position 275.
(Note: some scientists use 'N2 numbering' (H274Y) and some use 'N1 numbering' (H275Y))
This recent jump in resistance in Australia is concerning as these cases have not been linked to prior antiviral use or occurred in immunocompromised patients, factors commonly associated with the development of spontaneous resistance in the past.
Today the ECDC released a 5-page PDF risk assessment on the rise of resistant H1N1 cases in Australia. It concludes - that at least for now - “the risk of this cluster becoming more widespread and having public health implications remains low.”
It goes on to warn, however, that “only ongoing surveillance will indicate whether this occurrence remains a localised event or whether it has the potential to become widespread.”
You can read the abstract or download the entire document from the link below.
ECDC assessment on Oseltamivir-resistant influenza A(H1N1)2009 cluster reported in Australia
06 Sep 2011
Australia has reported oseltamivir resistance of A(H1N1)2009 influenza virus in the state of New South Wales, with assumed person-to-person transmission of the resistant strain. The European Centre of Disease Prevention and Control (ECDC) has produced a rapid risk assessment to assess the situation.
The oseltamivir-resistant cases had no known link to oseltamivir exposure and were not immunosuppressed, but were closely linked geographically. Samples from the cluster do not currently exhibit any resistance to zanamivir. Although the cluster has remained localised, it cannot be assumed that the variant virus will not spread.
ECDC concludes that at present, the risk of this cluster becoming more widespread and having public health implications remains low. However, if spread does occur, there will be implications for the prophylaxis and treatment of influenza patients and the consequences for public health in Europe will need to be considered.
Regardless of the outcome, constant antiviral resistance monitoring is vital in Europe and globally. Only ongoing surveillance will indicate whether this occurrence remains a localised event or whether it has the potential to become widespread.
Oseltamivir and zanamivir are active ingredients in antiviral drugs (Tamilfu, Relenza). Vaccination, supplemented by personal hygiene measures, remains the primary measure for prevention of seasonal influenza transmission. However, antiviral drugs are important countermeasures for prophylaxis and treatment, especially in vulnerable people and those with severe influenza.
Read the full ECDC risk assessment: Oseltamivir-resistant influenza A(H1N1)2009 cluster in Australia
