Genetic distances for the study of infectious disease epidemiology

Molecular epidemiologic studies of infectious pathogens 1) generate genetic patterns from a collection of microorganisms, 2) compare the degree of sim ilarity among these patterns, and 3) infer from these similarities infectio us disease transmission patterns. The authors propose a quantitative approa ch using genetic distances to study the degree of similarity between patter ns. Benefits of such genetic distance calculations are illustrated by an an alysis of standard DNA fingerprints of Mycobacterium tuberculosis in San Fr ancisco collected during the period 1991-1997. Graphical representation of genetic distances can assist in determining if the disappearance of a speci fic pattern in a community is due to interruption of transmission or ongoin g evolution of the microorganism's fingerprint. Genetic distances can also compensate for varying information content derived by DNA fingerprints of c ontrasting pattern complexity. To study demographic and clinical correlates of transmission, the authors calculated the smallest genetic distance from each patient sample to all other samples. With correlation of genetic dist ances and nearest genetic distances with previously understood notions of t he epidemiology of M, tuberculosis in San Francisco, factors influencing tr ansmission are investigated.