Increased sensitization in urban vs. rural environment – Rural protection or an urban living effect?

Abstract

In a population-based longitudinal cohort study, we tested the hypothesis that children growing up in a high-traffic polluted urban area (UA) in the Athens' basin have higher prevalence of allergies and sensitization when compared with those growing up in a Greek provincial rural area (RA). We recruited 478 and 342 children aged 8-10 living in the UA and the RA, respectively. Respiratory health was assessed by a parent-completed questionnaire in three phases: 1995-96 (phase 1), 1999-2000 (phase 2), 2003-04 (phase 3) and skin-prick testing to common indoor and outdoor aeroallergens was performed at phases 1 and 2. Reported asthma and eczema did not differ between the two areas, whereas reported hay fever was persistently more prevalent in the UA than in the RA (16.5%, 17.0%, 18.2% vs. 7.0%, 8.3%, 9.6%, respectively). Sensitization was more prevalent in the UA at both phases (19.0% vs. 12.1% in phase 1, 20.0% vs. 14.1% in phase 2). Residential area contributed independently to sensitization to >or=1 aeroallergens (OR: 0.29; 95% CI: 0.13-0.66; p = 0.003) and to polysensitization (OR: 0.28; 95% CI: 0.10-0.82; p = 0.020) in phase 1. These associations were independent of farming practices. No significant contributions were found in phase 2. Our results suggest that long-term exposure to urban environment is associated with a higher prevalence of hay fever but not of asthma or eczema. The negative association between rural living and the risk of atopy during childhood, which is independent of farming practices, implies that it is mainly driven by an urban living effect.

Some Epidemiological Aspects of Bronchial Asthma in Children in Qena Governorate, Egypt

“…On the contrary to our study, some researchers detected that rural children had increased asthma prevalence compared with urban children [31]. There is a suggestion that families who live in rural environments develop a level of immunity to plant and animal allergens that are typically associated with asthma [32,33] although others suggests that lower asthma rates in rural areas reflect lower urban-related risks rather than a rural protective effect [34]. The influence of environmental factors, especially air pollutants, has also been correlated with higher prevalence of asthma in the urban regions.…”

Human exposure to allergenic pollens: A comparison between urban and rural areas

“…NO 2 concentrations are high in urban areas because of traffic and heating. In addition to the risk of allergies linked to pollen exposure as shown in our study, the increase in pollinosis may be related to an increase in air pollutants in urban areas (Priftis et al, 2007). However, it is not yet clear whether hightraffic urban pollution partially enhances sensitization, or if it reduces tolerance to pollens in urban environments.…”

“…In epidemiological studies, rural and urban populations have not been exposed to the same pollen patterns (Hesselmar et al, 2001;MajkowskaWojciechowska et al, 2007;Priftis et al, 2007). This may constitute a bias in allergic status assessment.…”

“…This must be taken into account to improve estimates of sensitization. For instance, when the definition of an allergy is based on sensitivity to grass pollens, as it was in Priftis and colleagues' study (Priftis et al, 2007), a bias exists because city patients are exposed to grass pollen less often than country patients. The opposite could be true for city patients who are exposed to plane pollen, which is not often included in routine testing in large epidemiological studies.…”

“…Some studies have shown that the number of cases of pollinosis in cities is increasing (Behrendt et al, 1992;Heinrich and Wichmann, 2004) and that this disorder occurs more frequently in urban areas than in rural areas (Gonzalo-Garijo et al, 2006;Bousquet et al, 2008). In Greece, children living in urban areas are more sensitive to Poaceae pollen than children in rural areas (Priftis et al, 2007); pollinosis is also more frequent in Spain in urban areas (Armentia et al, 2001). These different levels of prevalence could be linked to the different atmospheric compositions of urban and rural areas.…”