Use of influenza antivirals in patients hospitalized in Hong Kong, 2000-2015

Objectives: We aimed to describe patterns in the usage of antivirals to treat influenza virus infection in hospitals in Hong Kong from 2000 through 2015. Methods: We analyzed centralized electronic health records that included dispensation information and diagnosis codes. Information collected on admissions included patient age, sex, admission year and month, and medications dispensed, and were matched with the first 15 discharge diagnosis codes. We divided monthly admission episodes by relevant population denominators to obtain admission rates, and stratified analyses by drug type, age group, and diagnosis codes. Results: Amantadine was used for influenza treatment in the early 2000s but changed with recommendations to avoid its use in 2006, and is now mainly used to treat Parkinson's disease. Oseltamivir usage increased substantially in 2009 and is now commonly used, with almost 40,000 hospitalizations treated with oseltamivir in the years 2012 through 2015, 66% of which was in persons ≥65 years of age. During the entire study period, of the 98,253 admission episodes in which oseltamivir was dispensed, 40,698 (41%) included a diagnosis code for influenza, and 80,283 (82%) included any diagnosis code for respiratory illness. Conclusions: The amount of oseltamivir used from 2012-15 was comparable to a separate ecological estimate of around 13,000 influenza-associated hospitalizations per year on average. We did not have access to individual patient laboratory testing data.