Effect of altitude on the frequency of pulmonary tuberculosis

SETTING: Pulmonary tuberculosis (PTB) incidence greatly varies around the world, a phenomenon usually attributed to socio-economic factors or health service availability. A recent study, however, indicated that PTB was inversely related to altitude.OBJECTIVE: To evaluate factors associated with PTB notification rates in Mexico.METHODS: Annual notification rates (1998-2002) of PTB in each of the 32 Mexican states were analysed, and likely factors were assessed through correlation and multiple regression analyses.RESULTS: Most variables lacked association with PTB rates, including percentage of population aged ≥65 years, population density, percentage of population with ≤2 minimum salaries, percentage of population with social security, level of education, diabetes incidence, percentage of immigration, percentage of rural population and a global marginalisation index. Only altitude above sea level correlated with tuberculosis incidence (r = −0.74, P < 0.0001). Likewise, in the multiple regression analysis only altitude reached a statistically significant association.CONCLUSION: Our results showed that altitude had a strong inverse relationship to PTB notification rates in Mexico, which might be related to the well known changes in alveolar oxygen pressure at different altitudes. Interestingly, several factors traditionally considered as predisposing conditions for the development of PTB did not correlate with the disease.