Objective: To investigate the association between the urban area of origin of patients and the prevalence of hypersensitivity pneumonitis (HP), induced by avian antigens.
Material and methods: A case-control study was conducted in 1999 at the National Institute of Respiratory Diseases (NIRD). Cases were 109 consecutive HP patients and controls were 184 patients: 39 with idiopathic pulmonary fibrosis (IPF), 63 with pulmonary tuberculosis (PTB), and 82 with asthma. Mexico City and surrounding counties (SC) were divided into 5 geographical areas: 1) Downtown; 2) North-East (NE); 3) South-East (SE); 4) North-West (NW) and 5) South-West (SW). Statistical analysis consisted of calculation of disease prevalence by urban area; associations were assessed with odds ratios and 95% confidence intervals. Multivariate analysis with multiple logistic regression was performed to adjust for age, gender and socioeconomic level.
Results: Eighty HP cases were located in the NE southernmost and SE northernmost areas of Mexico City (48 and 32, respectively) (OR = 3.86; 95% CI 2.17-6.96). Thirty-six controls with asthma came from the SW area, (where NIRD is located) (p < 0.05), and four from SC. Controls with PTB and IPF were scattered throughout the study area.
Conclusions: The NE southernmost and SE northernmost areas were associated with HP. The cause of HP may not be geographical; a garbage dump used to be located in this area, suggesting that exposure to organic particles might contribute to the development of HP in susceptible individuals.