Is systemic lupus erythematosus different in urban versus rural living environment? Data from the Cretan Lupus Epidemiology and Surveillance Registry

Background Examining urban-rural differences can provide insights into susceptibility or modifying factors of complex diseases, yet limited data exist on systemic lupus erythematosus (SLE). Objective To study SLE risk, manifestations and severity in relation to urban versus rural residence. Methodology Cross-sectional analysis of the Crete Lupus Registry. Demographics, residency history and clinical data were obtained from interviews and medical records (N=399 patients). Patients with exclusively urban, rural or mixed urban/rural residence up to enrolment were compared. Results The risk of SLE in urban versus rural areas was 2.08 (95% confidence interval: 1.66-2.61). Compared with rural, urban residence was associated with earlier (by almost seven years) disease diagnosis - despite comparable diagnostic delay - and lower female predominance (6.8:1 versus 15:1). Rural patients had fewer years of education and lower employment rates. Smoking was more frequent among urban, whereas pesticide use was increased among rural patients. A pattern of malar rash, photosensitivity, oral ulcers and arthritis was more prevalent in rural patients. Residence was not associated with organ damage although moderate/severe disease occurred more frequently among rural-living patients (multivariable adjusted odds ratio: 2.17, p=0.011). Conclusion Our data suggest that the living environment may influence the risk, gender bias and phenotype of SLE, not fully accounted for by sociodemographic factors.