Impact of oseltamivir on the incidence of secondary complications of influenza in adolescent and adult patients: results from a retrospective population-based study

Objective: To assess the effectiveness of oseltamivir in reducing the risks of influenza-related secondary complications in otherwise healthy adolescent and adult patients aged >= 13 years. Research design and methods: Retrospective cohort analysis utilizing health insurance claims data in the USA (Thomson MarketScan Research Database) from six influenza seasons (October-March) between 2000 and 2006 to identify adults and adolescents (>= 13 years) with influenza. Patients who received a prescription for oseltamivir within +/- 1 day of diagnosis were compared with a propensity-matched control group receiving no antiviral treatment. The first claim evidence of influenza was used to establish the study index date. Differences in outcomes were determined using Cox proportional hazards regression and expressed in terms of hazard ratios (HR) with 95% confidence intervals (CI). Main outcome measures., Diagnosis of pneumonia, any respiratory condition, otitis media and its complications, hospitalizations due to pneumonia, and hospitalization for any reason within 14 days of the index date. Healthcare expenditure within 30 days of the index date was also analyzed. Results: The oseltamivir and untreated control groups each included 36751 eligible patients. Oseltamivir use reduced the risks of otitis media and its complications by 23% (HR=0.77; 95% CI: 0.65, 0.93), any respiratory disease by 18% (HR 0.82; 95% CI: 0.79, 0.86), and hospitalization for any reason by 22% (HR 0.78; 95% CI: 0.67, 0.91). There were no differences in any other clinical outcomes, including hospitalization for respiratory disease. Healthcare expenditure did not differ between the two groups. Limitations:The retrospective nature of the study meant that the findings may be susceptible to missing or lost data. The results obtained here represent individuals enrolled in private healthcare plans and may not, therefore, be representative of the entire US population. The lack of a virologic diagnosis of influenza, and an index date based on the first diagnosis of influenza rather than first exposure or symptom onset, may have resulted in a conservative estimate of treatment effect. Conclusions: Secondary complications of influenza, such as respiratory disease and otitis media, were reduced in patients treated with oseltamivir. The risk of hospitalization for respiratory diseases was not reduced, although there was a reduction in the risk of hospitalization for any reason. Clinical benefits observed with oseltamivir were not associated with a change in healthcare costs.