Abstract
RATIONALE: Existing real-time surveillance of influenza morbidity, based primarily on time-trended U.S. hospitalization and death data, is inadequate. These surveillance methods do not accurately predict hospital resource requirements or sufficiently capture the public health impact of the current influenza season. OBJECTIVES: To determine the feasibility and potential usefulness of tracking surrogate markers of influenza morbidity among patients hospitalized with influenza. METHODS: We performed a pilot study at three tertiary care referral hospitals and retrospectively collected and analyzed data on patients admitted with influenza during the 2013-2014 influenza season. We analyzed traditional influenza surveillance metrics, including weekly statistics on admissions and deaths, as well as weekly rates and trends of intensive care unit (ICU), mechanical ventilation, and extracorporeal membrane oxygenation (ECMO) utilization. RESULTS: In our three-hospital cohort, 431 patients were hospitalized with influenza and spent a total of 1,520 days in ICUs. Eighty-six (20%) of these patients required 1,080 days of mechanical ventilation, and 17 patients (4%) received 229 days of ECMO. Trends of ICU and mechanical ventilation use were similar but differed notably from trends of ECMO use, hospitalization, and death. In particular, at two hospitals, increases in utilization of ICU and mechanical ventilation among patients with influenza occurred several weeks after increases in hospitalization rates. Furthermore, ICU, mechanical ventilation, and ECMO utilization rates at the three-hospital network remained elevated for several weeks after the influenza-associated hospitalization rate declined. CONCLUSIONS: Surrogate markers of influenza severity were feasible to collect and revealed trends of ICU resource utilization that differed notably from trends of hospitalization and death given by traditional influenza surveillance metrics. A national network of sentinel hospitals that prospectively collects, time-trends, and reports additional influenza morbidity data would be useful to hospital administrators, hospital epidemiologists, infection preventionists, and public health officials.