Urban-Rural Differences in the Epidemiology of Asthma and Allergies in Nigeria: A Population-Based Study.

Purpose: Urbanization is associated with the risk of developing allergic conditions. Few studies have evaluated the urban-rural disparity of allergic diseases in sub-Saharan Africa.

Objective: To compare the epidemiology of adult asthma and allergies in urban and rural Nigeria.

Subjects And Methods: A population-based cross-sectional study was performed among 910 subjects in Kwara State, North Central Nigeria, comprising 635 urban and 275 rural adults who were randomly selected. We used standardized questionnaires for data collection.

Results: The age-adjusted prevalence of adults reporting a previous "asthma attack" or "currently taking asthma medication" within the preceding 12 months (ECRHS asthma definition) was 3.4% urban, 0.5% rural, current allergic rhinoconjunctivitis (26.2% urban, 22.2% rural), and current skin allergy (13.9% urban, 10.5% rural). The age-adjusted prevalence of "physician-diagnosed allergic conditions": asthma (3.3% urban, 1.5% rural), allergic rhinoconjunctivitis (4.9% urban, 3.2% rural), and skin allergy (4.8% urban, 4.6% rural) were higher in urban areas than in rural areas. Urban areas recorded a higher age-adjusted 12 months prevalence of wheezing, night waking by breathlessness, night waking by chest tightness, asthma attack (p=0.042), and current use of asthma medication (p=0.031) than the rural areas. In the urban areas, 81% of those with asthma significantly had current allergic rhinoconjunctivitis, and 40.5% had current skin allergy, whereas in the rural areas, all subjects with asthma had current allergic rhinoconjunctivitis and 12.5% had current skin allergy (p=0.482). The most common trigger for asthma attack/respiratory symptoms among the urban household was exposure to environmental smoke (17.2%), and among the rural household, it was dust exposure (18.2%). Living in urban areas significantly increased the odds of having asthma [aOR: 5.6 (95% CI:1.6-19.6)] and allergic rhinoconjunctivitis [aOR: 1.7 (95% CI: 1.2-2.4)].

Conclusion: This study shows that urban residents frequently reported more allergic and respiratory symptoms and were at risk of having asthma and allergic rhinitis compared to rural residents. The findings would assist the physicians in understanding the urban-rural differences in the occurrence of allergic conditions, symptom triggers, and comorbidity, which are relevant in patient's clinical evaluation, treatment, and disease prevention.