Economic Outcomes of Influenza in Hospitalized Elderly with and without ICU Admission

BACKGROUND: To describe direct medical costs of influenza in hospitalized elderly, with and without intensive care unit (ICU) admission, during the 2014-2015 season in Hong Kong. METHODS: A retrospective study was conducted in 110 inpatients aged ≥65 years with laboratory-confirmed influenza treated by antiviral therapy during season 2014-2015 in a tertiary hospital. Resource utilization of influenza-related diagnostic and laboratory tests, medications for influenza treatment, usage of general medical ward and ICU during the influenza-related length of hospital stay (IR-LOS) were collected. RESULTS: There were 18 (16.4%) and 92 (83.4%) cases with and without ICU admission, respectively. The difference in influenza-related mortality rates between patients with (11.1%) and without ICU admission (2.2%) was not statistically significant (P=0.064). Patients with ICU admission reported longer IR-LOS (12.7 ±6.0 days versus 5.5 ±2.7 days; P<0.001) and higher direct costs (36,588 USD ±21,482 versus 5,773 USD ±2,017; P<0.001; 1 USD=7.8 HKD). Male gender (OR=14.50; 95% CI 1.68, 125.07) and respiratory complications (OR=9.61; 95% CI 1.90, 48.50) were positive predictors of ICU admission. Age ≥70 years (OR=0.09; 95% CI 0.02, 0.46) and antiviral therapy initiation within 7 days (OR=0.05; 95% CI 0.003, 0.79) were negative predictors of ICU admission. Influenza B was a positive predictor of high-cost hospitalization in non-ICU survivors (OR=7.33; 95% CI 1.24, 43.29). No predictor of mortality was identified. CONCLUSIONS: Hospitalization cost in elderly for seasonal influenza was substantial in Hong Kong. The cost in patients with ICU admission was significantly higher than those without ICU care. Respiratory complications and male gender predicted ICU admission. Influenza B infection predicted high-cost hospitalization in non-ICU survivors.