Evaluation of the Effectiveness of Oseltamivir for the Treatment of 2009 Pandemic Influenza A (H1N1)

Aims: Evaluate retrospectively the effectiveness of treatment with oseltamivir in a Brazilian subpopulation infected during the 2009 pandemic influenza A(H1N1) and compare drug activity based on the presence or absence of other disease risk factors and also the time from onset of symptoms to initiation of treatment.
Study Design: Observational and retrospective.
Place and Duration of Study: Federal University of Paraná and Parana State Secretary of Health, between April 2009 and December 2010.
Methodology: 1,917 patients were included (842 men, 1,075 women; age range 0-90 years) with positive diagnosis for the 2009 influenza virus A (H1N1) characterized by RT-PCR, whose notification forms were available at the time of data collection and that contained information of the use or not of oseltamivir. The patients were categorized by age, gender, symptoms, presence or absence of co morbidities, outcomes (cure or death) and treated or untreated with oseltamivir. The odds ratio (OR) was estimated using a multivariate logistic regression analysis. Kaplan-Meier method was used to determine if differences existed between the survival of untreated patients and oseltamivir treated patients.
Results: Out of 1,917 patients, 1,644 had cleared the infection and 273 patients died. Age, education level, cardiopathies, nephropathies, immunodepression, smoking, diabetes, systemic arterial hypertension, obesity, diarrhea, dyspnea, hemoptysis and pneumonia were considered risk factors. The use of oseltamivir provided about 32.3 times more likely to clear the infection compared with untreated patients. Moreover, the effectiveness of oseltamivir is reduced by approximately 7-fold in smoking patients. For each day that passed to initiate treatment after the onset of symptoms, the risk of death increased by 32.3%.
Conclusion: The findings suggest that treatment with oseltamivir was effective in producing favorable patient outcomes in those who contracted the 2009 influenza A (H1N1) strain.