Background-There is increasing evidence that environmental factors contribute to the development of asthma, so the relationship was studied between home environment factors and asthma among school children of varying socioeconomic backgrounds living in a developing country. Methods -A case-control study was performed in participants ofa prevalence survey which included 77 schoolchildren with asthma (defined by a history of wheeze, doctor diagnosis, or a decline in FEVy of ) 10% at five or 10 minutes after exercise) and 77 age and gender matched controls. Subjects were selected from 402 school children aged 9-11 years attending five primary schools in the city of Nairobi who participated in a prevalence survey of asthma. Visits were made to the homes of cases and controls and visual inspection of the home environment was made using a checklist. A questionnaire regarding supplemental salt intake, parental occupation, cooking fuels, and health of all children in the family was administered by an interviewer. Results -In multivariate analysis the following factors were associated with asthma: damage caused by dampness in the child's sleeping area (adjusted odds ratio (OR) 4-9; 95% confidence interval (CI) 2-0 to 11.7), air pollution in the home (OR 2 5; 95% CI 2-0 to 6.4), presence of rugs or carpets in child's bedroom (OR 3 6; 95% CI 1 5 to 8 5). Children with asthma reported a supplemental mean daily salt intake of 817 mg compared with 483 mg in controls. Conclusions -Home environmental factors appear to be strongly associated with asthma in schoolchildren in a developing nation. These findings suggest a number of hypotheses for further studies. (Thorax 1995:50:74-78)

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