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Biosecurity BriefingWHO Reports Oseltamivir Resistance in Southern HemisphereBy Jennifer Nuzzo, August 25, 2008 On August 15, 2008, the World Health Organization (WHO) issued a report indicating that clinical samples from the 2008 influenza season provide evidence of a high degree of resistance to the antiviral drug oseltamivir (Tamiflu®). According to WHO, there have been “several reports from National Influenza Centres in the southern hemisphere regarding influenza A (H1N1) virus resistance to oseltamivir.”1 WHO’s report focuses on South Africa, where 139 clinical samples were isolated thus far during the 2008 influenza season. A 107-isolate subsample was tested for oseltamivir resistance, and 100% were found to be resistant to oseltamivir by genetic analysis; just one of the 107 patients with resistant strains had been receiving oseltamivir at the time of sampling. None of the 107 patients was reported to have unusual clinical features or underlying conditions. In a news report from Bloomberg, Terry Besselaar, director of South Africa's National Influenza Centre in Johannesburg commented, “The patients are from across the country, so the resistant strain is widespread.”2 The WHO report also notes that 10 of 10 A(H1N1) viruses isolated and tested in Australia, and 4 of 32 A(H1N1) viruses isolated and tested in Chile, were found to have the genetic mutation that has been associated with oseltamivir resistance. According to Bloomberg, oseltamivir resistance has been reported in 40 countries in Europe, North and South America, Africa, Asia and Australia since January. A representative from Roche, which manufactures Tamiflu®, said the company is planning “to conduct a resistance surveillance study to collect information on both the sensitive and resistant influenza infections during the 2008-2009 flu season.”2 In a summary of the findings, the European Centre for Disease Control and Prevention (ECDC) stated that, while the significance of these findings remains uncertain, the “emergence of drug resistance in the context of limited drug use is unexpected, and the extent of future circulation is difficult to predict.”3 Although there is currently no evidence that resistance is related to the use of the medicine, the ECDC will work with Roche to conduct additional surveillance and testing.2 References
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