Characteristics derived from outbreaks of pandemic influenza A (H1N1) 2009 virus.

tamivir-resistant A (H1N1) infections that were treated with oseltamivir reported a shorter duration of cough; however, no other differences were found. We also compared the proportion of patients who reported fever, cough, sore throat, chills, myalgia or arthralgia, and difficulty breathing. Patients with oseltamivir-resistant A (H1N1) infection that was treated with oseltamivir were less likely to report difficulty breathing. However, because we did not collect information on when symptoms occurred with respect to the initiation of treatment, these results are difficult to interpret. Although treated persons with oseltamivir-susceptible infection tended to show milder disease and faster recovery than those who were not treated, several differences did not reach statistical significance. These comparisons may have reached statistical significance if we had a larger cohort or if more information were available, including time to resolution of all symptoms. Our study was nonrandomized; the few variables that were statistically different among treated and untreated persons with oseltamivir-resistant infection may be due to unaccountable confounders. In conclusion, our results do not support the use of oseltamivir in patients with oseltamivir-resistant influenza virus infection and are consistent with laboratory antiviral tests. Additional studies may provide further information in correlating laboratory-determined antiviral resistance with clinical response to treatment.