Molecular epidemiology: focus on infection.

Molecular biology techniques have become increasingly integrated into the practice of infectious disease epidemiology. The term "molecular epidemiology" routinely appears in the titles of articles that use molecular strain-typing ("fingerprinting") techniques-regardless of whether there is any epidemiologic application. What distinguishes molecular epidemiology is both the "molecular," the use of the techniques of molecular biology, and the "epidemiology," the study of the distribution and determinants of disease occurrence in human populations. The authors review various definitions of molecular epidemiology. They then comment on the range of molecular techniques available and present some examples of the benefits and challenges of applying these techniques to infectious agents and their affected host using tuberculosis and urinary tract infection as examples. They close with some thoughts about training future epidemiologists to best take advantage of the new opportunities that arise from integrating epidemiologic methods with modern molecular biology.