Epidemiology

About 2000 million people in the world today are infected with tuberculosis,1 but only 10% develop clinical disease. Why some people develop clinical disease remains unclear. The reasons are likely to be multifactorial: inherent not just to the individual person, but to their given population and environment.

Before HIV the most important determinant for the development of TBM was age. In populations with high TB prevalence TBM differs from pulmonary, and other extrapulmonary tuberculosis, in that the peak age is from 0–4 years.2 In populations with lower TB prevalence, most cases of TBM are in adults. Risk factors identified for these people are alcoholism, diabetes mellitus, malignancy, and recent corticosteroid use.3-5 Coinfection with HIV now dwarfs these risk factors. HIV increases the lifetime risk of developing clinical TB postinfection to 1 in 3.6 HIV also predisposes to the development of extrapulmonary TB, and in particular TBM,7 a risk which increases as the CD4 count declines.8 The disease constitutes either reactivation of latent infection, or new infection. Evidence from DNA fingerprinting of strains using restriction fragment length polymorphism suggests …