Molecular epidemiology of tuberculosis.

Molecular epidemiology (ME), a blend of molecular biology and epidemiology, is very useful to study the spread of tubercle bacilli in mini epidemics, outbreaks, to analyse the transmission dynamics of tuberculosis (TB) and to determine the risk factors for TB transmission in a community. ME has a great role in distinguishing between exogenous reinfection and endogenous reactivation. In the laboratory, molecular epidemiology can be used to identify cross contamination. Many new DNA typing methods have been introduced after the initial introduction of restriction fragment length polymorphism (RFLP) in 1993. An internationally accepted, standardized protocol for RFLP typing of the Mycobacterium tuberculosis complex using IS6110 was published in 1993 and is still used today. Most of the newer DNA typing methods are PCR based and microarray based methods are also available. This will enable individual strains of M. tuberculosis or clonal groups to be identified by specific phenotypic traits. ME will continue to be a useful tool in future to measure the impact of any public health intervention strategy for control of tuberculosis in the community.