Introduction and Historical Perspective

The term molecular epidemiology emerged apparently independently during the 1970s to early 1980s in the literature of three separate substantive areas of epidemiology: cancer epidemiology, environmental epidemiology, and infectious disease epidemiology. Although these separate substantive areas agree that epidemiology refers to the distribution of disease in a population and the determinants of that distribution, the literature presents conflicting definitions of what makes a study a molecular epidemiologic study. In cancer and environmental epidemiology, molecular is defined almost exclusively in terms of biomarkers. However, biomarkers are only one type of molecular measure, and this definition ignores the many applications of molecular methods in genetic and infectious disease epidemiology. Early epidemiologists made tremendous strides with what are now relatively simple molecular tools, such as using microscopy for identification, showing agents not visible by microscope cause disease, and detecting protective antibodies with hemagglutination assays. In the microbiology literature, molecular epidemiology has become synonymous with the use of molecular fingerprints—regardless of whether the study was population based or met other criteria consistent with an epidemiologic study. Moreover, the molecular tools available, and the potential for applications for studies of populations, have changed substantially since the term molecular epidemiology was coined.