Short-term effect of concentrations of fine particulate matter on hospital admissions due to cardiovascular and respiratory causes among the over-75 age group in Madrid, Spain.

OBJECTIVES

This study sought to analyse the effect of daily mean concentrations of fine particulate matter (diameter <2.5 microm; PM(2.5)) on hospital admissions due to circulatory and respiratory causes among an elderly population (>75 years) in Madrid between 2003 and 2005.

STUDY DESIGN

Ecological longitudinal time-series study.

METHODS

The dependent variable used was the daily number of emergency hospital admissions registered at the Gregorio Marañón University Teaching Hospital. The following causes were analysed: all causes [International Classification of Diseases 9th Version (ICD-9:1-799)], respiratory causes (ICD-9: 460-519) and circulatory causes (ICD-9: 390-459). Analysis focused on subjects over 75 years of age. Daily records of mean concentrations of PM(2.5), PM(10), NO(2), NO(x), SO(2) and O(3) in Madrid were used as independent variables. The control variables were seasonalities, trend, influenza epidemics, noise and pollen concentrations. Poisson regression models were constructed to calculate the relative risk (RR) and attributable risk (AR). Analyses were performed for the entire year and for the winter and summer.

RESULTS

PM(2.5) was the single primary pollutant that proved statistically significant in all models. The functional relationship with hospital admissions was linear and had no threshold. Taking the year as a whole, the RRs among people over 75 years of age for an increase of 10 microg/m(3) in PM(2.5) concentrations were: 1.038 [95% confidence interval (CI) 1.022-1.053] for all causes at lag 0; 1.062 (95% CI 1.036-1.089) for circulatory causes at lag 0; and 1.049 (95% CI 1.019-1.078) for respiratory causes at lag 3. The ARs were 3.6%, 5.9% and 4.6%, respectively. These risks increased in winter and no statistically significant associations were observed in summer. PM(2.5) was the only primary pollutant that showed a statistically significant association with hospital admissions among people over 75 years of age in Madrid across the study period.

CONCLUSION

Measures should be implemented to reduce PM(2.5) concentrations in Madrid.