Is there an explanation for the high frequency of oseltamivir resistance?
The frequency of oseltamivir resistance in H1N1 viruses in the current influenza season is unexpected and the reason why a high percentage of these viruses are resistant is currently unknown. Available information does not indicate selective drug pressure is driving the development of resistance since few of the patients are known to have taken oseltamivir. Influenza viruses are continuously changing and it is possible that a resistant strain has emerged spontaneously or has continued to spread in the community after being selected initially in someone treated with oseltamivir. Further detailed laboratory characterization of circulating H1N1 viruses and epidemiological information on patients will be needed to help answer this question.
