Purpose: The objective of the study is to evaluate the effect of antiviral treatment, pre-existing diseases, and sociodemographic factors on the risk of influenza-related complications and healthcare utilization.
Methods: Case data was obtained from U.S. MarketScan Research Databases. Cases had a clinical diagnosis of influenza between 2006 and 2010 and continuous healthcare insurance from 90 days before to 30 days after diagnosis. Logistic regression models were applied to explore the impact of antiviral treatment on complications and healthcare utilization. Modified generalized estimating equation regression models in propensity score matched samples were used to address the robustness of the study.
Results: Analyses included 1,557,437 cases from four influenza seasons. In each season, 34.82%-43.42% of patients received antiviral treatment, mostly oseltamivir. On average, 1.86% of patients were hospitalized, 9.56% visited the emergency room and 41.14% made ≥2 outpatient visits. The incidence of complications ranged from 17.62 to 19.67 per 100 patient-months. The relative risk of complications was increased in patients aged 0-4 years and those with pre-existing diseases, including asthma, Parkinson's disease, and cystic fibrosis. Overall, patients receiving antiviral treatment had an 11% reduction in the risk of complications. Among oseltamivir-treated patients, the risk of complications was significantly reduced by 81% in those treated ≤2 days after diagnosis compared with later. Antiviral treatment significantly reduced the risk of hospitalization, emergency room visits and need for ≥2 outpatient visits by 29%, 24% and 11%, respectively. The propensity score matching method improved the strength of the study.
Conclusions: Early treatment with antivirals, and specifically oseltamivir, significantly reduced the risk of influenza-related complications and healthcare utilization. However, lacking information about disease severity and the time from onset of symptoms to fulfillment of a prescription may bias the outcomes.
Keywords: Antiviral; claims database; complications; influenza; oseltamivir.