Mortality caused by influenza and respiratory syncytial virus by age group in England and Wales 1999-2010.

BACKGROUND

The mortality burden caused by influenza cannot be quantified directly from death certificates because of under-recording; therefore, the estimated number of influenza deaths has to be obtained through statistical modelling.

OBJECTIVE

To estimate the number of deaths caused by influenza and respiratory syncytial virus (RSV) in England and Wales between 1999 and 2010 using a multivariable regression model.

METHODS

Generalised linear models were used to estimate weekly deaths by age group (<15, 15-44, 45-74 and 75+ years) as a function of positive influenza and RSV isolates. Adjustment was made for temperature variation (using weekly means of daily Central England temperature time series), underlying seasonal variation and temporal trends. The parameters from the model were used to predict the number of deaths caused by influenza and RSV across winter seasons.

RESULTS

Between 7000 and 25 000 deaths across all ages were associated with influenza in the winter periods 1999-2009. The mortality burden was the highest among the over 75 age group, among whom 2·5-8·1% of deaths were caused by influenza. The lowest number of influenza deaths was estimated for the winter 2009/2010 when pandemic influenza A/H1N1 (2009) was the predominant circulating strain. RSV accounted for 5000-7500 deaths each winter season.

CONCLUSIONS

The model presented provides a robust and reasonable approach to estimating the number of deaths caused by influenza and RSV by age group at the end of each winter.