Altitude: a determinant for tuberculosis in Kenya?

OBJECTIVE: To determine to what extent tuberculosis incidence is associated with altitude.METHODS: Notification rates were obtained from all 41 districts in Kenya in the period 1988-1990; the mean altitude of each district was estimated. Data on indicators of socio-economic status such as literacy rate and infant mortality rate were obtained from the 1989 census, as well as data on other potential confounders such as urbanisation and median household size.RESULTS: The notification rate of new smear-positive tuberculosis was 32/100 000 overall, varying between districts from 5 to 222/100000. Notification rates steeply reduced with increasing altitude (r = −0.71; 95% confidence interval [CI] −0.51 to −0.83). At altitudes of 1000 m or more the notification rates were less than 30% of those in districts at altitudes below 500 m, also after adjustment for confounding.CONCLUSION: Tuberculosis incidence in Kenya decreases strongly with increasing altitude. If the association is not due to unknown confounding factors, a range of potential biological explanations needs to be explored.