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Open Access Research article

Modeling the cost of influenza: the impact of missing costs of unreported complications and sick leave

Yiting Xue12*, Ivar Sønbø Kristiansen3 and Birgitte Freiesleben de Blasio12

Author Affiliations

1 Department of Biostatistics, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway

2 Division of Infectious Disease Control, Norwegian Institute of Public Health, Oslo, Norway

3 Institute of Health Management and Health Economics, University of Oslo, Oslo, Norway

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BMC Public Health 2010, 10:724  doi:10.1186/1471-2458-10-724

Published: 24 November 2010

Abstract

Background

Estimating the economic impact of influenza is complicated because the disease may have non-specific symptoms, and many patients with influenza are registered with other diagnoses. Furthermore, in some countries like Norway, employees can be on paid sick leave for a specified number of days without a doctor's certificate ("self-reported sick leave") and these sick leaves are not registered. Both problems result in gaps in the existing literature: costs associated with influenza-related illness and self-reported sick leave are rarely included. The aim of this study was to improve estimates of total influenza-related health-care costs and productivity losses by estimating these missing costs.

Methods

Using Norwegian data, the weekly numbers of influenza-attributable hospital admissions and certified sick leaves registered with other diagnoses were estimated from influenza-like illness surveillance data using quasi-Poisson regression. The number of self-reported sick leaves was estimated using a Monte-Carlo simulation model of illness recovery curves based on the number of certified sick leaves. A probabilistic sensitivity analysis was conducted on the economic outcomes.

Results

During the 1998/99 through 2005/06 influenza seasons, the models estimated an annual average of 2700 excess influenza-associated hospitalizations in Norway, of which 16% were registered as influenza, 51% as pneumonia and 33% were registered with other diagnoses. The direct cost of seasonal influenza totaled US$22 million annually, including costs of pharmaceuticals and outpatient services. The annual average number of working days lost was predicted at 793 000, resulting in an estimated productivity loss of US$231 million. Self-reported sick leave accounted for approximately one-third of the total indirect cost. During a pandemic, the total cost could rise to over US$800 million.

Conclusions

Influenza places a considerable burden on patients and society with indirect costs greatly exceeding direct costs. The cost of influenza-attributable complications and the cost of self-reported sick leave represent a considerable part of the economic burden of influenza.