Molecular answers to tuberculous questions

Molecular epidemiology enables us to ask various questions. Are the chains of transmission assumed from contact tracing correct? Are relapse cases true relapse or reinfection? What is the contribution to disease of recent transmission versus reactivation? Quantification of genotypically identical isolates enables one to estimate the contribution of recent transmission to the epidemic. These estimates vary from about 20% to 50%; thus, reactivation disease seems to form a major component of the epidemic in all societies. If this conclusion is correct, it has major implications for health-care provision and policy development. The increasing incidence of tuberculosis in many parts of the world is therefore not unexpected, in the absence of the identification of all cases of infection and disease. There is therefore an argument for population-screening for active and latent cases.