Is there a rural/urban gradient in the prevalence of eczema? A systematic review

P>Background Eczema affects approximately 10% of all schoolchildren in the western world and has shown an increase over the past decades in 'developing' countries. Numerous factors have been suggested that might contribute to the increasing prevalence of eczema. A plausible explanation is the role of environmental factors. As part of the 'hygiene hypothesis' it has been thought that eczema is more common in urban than in rural communities, but such a notion has never been assessed systematically. Objective Our aim was to assess whether there is a rural/urban gradient for the prevalence of eczema and, if so, to what extent. Methods All data sources were identified through a search in MEDLINE and EMBASE. All primary studies comparing the prevalence rate of eczema between urban and rural populations were assessed for eligibility. Included articles were reviewed for methodological quality and a relative risk was calculated to indicate the risk of eczema in urban over rural areas. Results Twenty-six articles were included for analysis. Nineteen showed a higher risk for eczema in an urbanized area, of which 11 were significant. Six studies showed a lower risk of eczema in an urbanized area, of which one was statistically significant. One study had a relative risk of 1 center dot 00. Results were more homogeneous among studies of good methodological quality. A pooled relative risk could have been calculated but was not because of heterogeneity. Conclusion There is some evidence of a higher risk for eczema in urban compared with rural areas, suggesting that place of residence may have a role in the pathogenesis of eczema. Future reviews on environmental circumstances should be carried out to reveal the factors associated with a higher prevalence of eczema in urban areas and the association with other allergic disease