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

Summary

Objectives

This study sought to analyse the effect of daily mean concentrations of fine particulate matter (diameter <2.5 μm; 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, PM₁₀, NO₂, NO_x, SO₂ and O₃ 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 μg/m³ 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.

Introduction

In an urban atmosphere, particulate matter with a diameter of less than 2.5 μm (PM_2.5), known as ‘fine particulate matter’, mainly originates from road traffic emissions and, more specifically, from diesel-powered vehicles.¹ Some studies show that, possibly due to the steady increase in use of diesel vehicles in recent years, levels of PM_2.5 have risen notably in recent decades.² This has led to air-quality limits being exceeded in European urban areas, and to the notion that PM_2.5 should be regarded as a primary pollutant of great importance in Europe. Furthermore, in 2005, the World Health Organization (WHO) laid down certain health protection guideline values based on ground-level concentrations of PM_2.5.³ In addition, at a legislative level, the European Union issued a Directive in 2008 that establishes the limits for this pollutant until 2020.⁴

The relatively recent interest in this pollutant in Europe means that few cities have measured it routinely. Therefore, there are no data series covering a sufficiently long period of time, and relatively few epidemiological studies have been undertaken in a European setting which address the health effects of PM_2.5. This situation clearly contrasts with the extensive knowledge of this pollutant in other parts of the world, particularly the USA, where its effects on morbidity and mortality have been studied extensively. The US Environmental Protection Agency has laid down reference values that are more restrictive than those stipulated in the European enactment.⁵

Insofar as the health effects of PM_2.5 are concerned, based upon studies conducted in America and some European cities, cardiorespiratory diseases are most affected by an increase in PM_2.5 concentrations.6, 7, 8 More specifically, PM_2.5 concentrations have been associated with increases in mortality due to cardio- and cerebrovascular causes, and increases in hospital admissions due to myocardial infarction and stroke.9, 10 PM_2.5 has also been linked with heart rate variability,11, 12 increased blood pressure,13, 14 coronary atherosclerosis,¹⁵ worsening of ischaemic diseases, arrhythmias and infarctions,8, 16, 17, 18 and heart failure in general.¹⁹

From the standpoint of respiratory diseases, PM_2.5 concentrations affect pulmonary function, with a decrease in peak flow,20, 21, 22 a worsening of chronic obstructive pulmonary disease,⁹ and a rise in admissions due to respiratory diseases.23, 24 These effects are particularly aggravated among older age groups.7, 8, 11, 13, 25

To date, however, few studies have sought to relate the effect of PM_2.5 concentrations on hospital admissions among the most advanced age groups in European Mediterranean countries, with the characteristics of climate and pollutant spread which are peculiar to such countries and differentiate them from other places in Europe. For instance, specific Mediterranean climatic conditions may tend to make for pollution episodes, such as low precipitation which militates against the air being cleared. Concomitance of chronic diseases and deterioration in general health status is readily found in subjects over 75 years of age; something that renders this group particularly vulnerable to the impact of air pollution.

In Spain, 70% of readings taken at the country's air-quality monitoring and control stations exceed the daily limit value for particulate matter set in 2005.²⁶ In addition, the number of diesel vehicles has increased in recent years, soaring from 2,800,000 vehicles in 1997 to over 8,400,000 in 2005, with a growing trend in recent years.¹ Moreover, there is an evident ageing pattern in the Spanish population. Accordingly, this study sought to analyse the effect of daily mean PM_2.5 concentrations on hospital admissions due to circulatory and respiratory causes among people over 75 years of age in a city with a heavy traffic density, such as Madrid.