**4. Molecular epidemiology of MDR-TB**

#### **4.1. Molecular epidemiology**

Many different definitions of molecular epidemiology have been published and all mention the use of molecular tools, but not all explicitly mention epidemiology. Molecular epidemiol‐ ogy is not just molecular taxonomy, phylogeny, or population genetics but the application of these techniques to epidemiologic problems [39]. Epidemiology attempts to identify factors that determine disease distribution in time and place, as well as factors that determine disease transmission, manifestation, and progression. Further, epidemiology is always motivated by an opportunity or possibility for intervention and prevention [39]. What distinguishes molecular epidemiology is both the "molecular," the use of the techniques of molecular biology to characterize nucleic acid- or amino acid-based content, and the "epidemiology," the study of the distribution and determinants of disease occurrence in human populations [39]. Molecular epidemiology makes use of the genetic diversity within strains of infectious organisms to track the transmission of these organisms in human populations and to evaluate the host and parasite -specific risk factors for disease spread.

Therefore molecular epidemiologic techniques can be incorporated into almost any epide‐ miologic assessment to improve exposure and outcome measures
