Urban background particulate matter and allergic sensitization in adults of ECRHS II

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Abstract

Background

Epidemiological studies have shown weak or inconsistent associations between ambient air pollutants and allergic sensitization. The aim of this study was to evaluate whether regional urban air pollution may partly explain the large variation in the prevalence of allergic sensitization across cities of the European Community Respiratory Health Survey (ECRHS) II.

Methods

ECRHS is a cross-sectional survey initiated in 29 countries across Europe in the 1990s (ECRHS I) with a follow-up conducted 10 years later (ECRHS II). Subject characteristics were measured by questionnaires and blood tests conducted for the measurement of specific immunoglobulin E. Fine particle mass (PM2.5, <2.5 μm) and sulphur on PM2.5 were measured in 21 centres and annual averages of urban regional background air pollution were calculated. Results were scaled by an interquartile range increase in ambient PM2.5 (6.03 μg/m3) and sulphur (1336 ng/m3). Generalized estimating equations were applied to compute population average effect estimates with adjustment for age, gender, smoking habit, education and number of siblings.

Results

A notable variation in pollution level and prevalence of allergic sensitization was observed. Moreover, exposure to urban regional background air pollution was not associated with allergic sensitization; adjusted odds ratios and 95% confidence interval were 1.02 (0.95–1.09) for PM2.5 and 1.08 (0.86–1.31) for sulphur. These statistically non-significant associations were sensitive to model specification.

Conclusions

The study suggests that regional air pollution measured at fixed sites is not associated with allergic sensitization among adults in ECRHS II.

Introduction

According to growing empirical evidence, the prevalence of atopic diseases and allergy has increased in a number of developed countries among children and adults (Upton et al., 2000; Maziak et al., 2003) although atopic diseases and asthma prevalence may have plateaued in recent years, particularly among adults (von Hertzen, 2005; Braun-Fahrlander et al., 2004). The rise in allergy is generally attributed to the western life style and environmental factors and does not seem to reflect changes in genetic factors (von Hertzen and Haahtela, 2004; Ronchetti et al., 2001). Although, a number of factors are assumed to be responsible for the increased prevalence of atopy and allergic diseases, an association with increased exposure to traffic-related pollution has been proposed besides life-style changes in microbial stimulation of the immune system. Since allergic diseases are important public health problems, the need to identify causes and contributing factors is irrefutable.

Epidemiological research, human and animal experimental studies have demonstrated a diverse role of pollutants in relation to allergy. However, the underlying mechanisms by which pollutants exert effects are still unclear. A number of experimental and toxicological studies in humans and animals using different methods have shown a variety of inflammatory and immunological reactions to short exposure to particulate matter (PM) and diesel exhaust particles (Heinrich et al., 2005a; Diaz Sanchez, 1997; Nel et al., 1998; Riedl and Diaz-Sanchez, 2005). Pollutants may have a role as triggers for new onset of allergy or in exacerbating existing allergic disease. In addition, they have been suggested to be adjuvant for immunoglobulin E (IgE) and contributing to the increased global allergen production (Riedl and Diaz-Sanchez, 2005; Bernstein et al., 2004).

Numerous epidemiological studies have documented an association between air pollutants and allergic diseases, although these associations were at times inconsistent (Heinrich and Wichmann, 2004). Studies from different countries have shown that both adults and children living close to main and busy roads have an increased risk of allergic disease and respiratory symptoms (Kramer et al., 2000; Venn et al., 2001; Wyler et al., 2000). Other studies have not found such an association (Livingstone et al., 1996; Nicolai et al., 2003). Epidemiological air pollution studies have used a variety of exposure assessment methods such as subjective proxy measures of self-reported distance from heavy traffic and traffic density as well as objective traffic counts, geographical information systems (GIS) and measurement of ambient pollutants from central sites (Heinrich and Wichmann, 2004). Several studies have shown that for regional air pollution such as fine particle mass concentration, and in particular sulphate and sulphur mass concentration on PM, fixed site monitors can serve as good proxy for personal exposure across the community (Oglesby et al., 2000; Brunekreef et al., 2005).

The European Community Respiratory Health Survey (ECRHS) is a cross-sectional multi-centre study of adults originally aged 20–44 years (ECRHS I) (Burney et al., 1994) that were followed for nearly 10 years (ECRHS II) (Jarvis, 2002). Both surveys included initial screening questionnaires, extensive interviewer led questionnaires, blood test for IgE, spirometry, methacholine challenge tests and skin prick tests. The objective of the current analysis is to investigate the prevalence of allergic sensitization and its relation to regional air pollutants in the follow-up of cohorts of ECRHS II in 21 participating centres where additional air pollution measurement were made.

Section snippets

Study design

ECRHS is a multi-centre survey conducted in 29 centres in Europe. Its protocol has been extensively described elsewhere (Burney et al., 1994; Jarvis, 2002) and additional information is also accessible on www.ecrhs.org. The cross-sectional survey was initiated in 22 countries in 1990 as ECRHS I and follow-up was conducted in 2000/01 as ECRHS II. The current analysis relates to participants in ECRHS II.

Study population

Subjects for the present study were defined as all those participants of ECRHS II who

General characteristics of the study population

Table 1 shows the number of participants at different stages of ECRHS II by centre. 12,940 subjects were eligible for ECRHS II out of which 10,051(77.68%) responded to the screening questionnaire, 8367(64.66%) to the main questionnaire. Half of the subjects (50.03%) had gone through blood tests for IgE measurement. Characteristics about the study participants and sensitization status are shown in Table 2. The mean age±SD of the study population was 42.78±7.20 years. The F:M sex ratio was

Discussion

This follow-up cohort of a large population based survey has investigated the relation between allergic sensitization and ambient air pollutants in 21 centres across Europe. The study has found no clear association between air pollutants and allergic sensitization measured by specific IgE. The small observed association was not statistically significant and rather unstable in the sensitivity analyses. Exclusion of Italy (i.e. the three locations with the highest pollution) and analyses without

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