K: Genetic fingerprinting in the study of tuberculosis transmission

The epidemiology of infectious diseases has traditionally relied on observedpatterns of occurrence to infer transmission. In the case of a disease with avariable incubation period, such as tuberculosis (TB), a series of overlap-ping micro-epidemics can appear as a relatively steady notification rate at the popu-lation level. Recently, genetic fingerprinting has been used in epidemiologic studies to begin to assess such TB micro-epidemics. A crucial aspect of any TB control program is the ability to determine where transmission is occurring in order to prevent further spread of infection and pre-vent active disease by identifying newly infected people and providing them with preventive therapy. Genetic fingerprinting of Mycobacterium tuberculosis has vastly improved our ability to observe patterns of transmission in populations. It has helped to establish transmission links between individuals and to demonstrate in-stances in which related people were infected with unrelated strains. Since the 1980s the number of TB cases reported annually in Canada has been stable, at about 2000, translating into an incidence rate of about 7 cases per 100 000 annually.1 During this time, however, the groups at risk have changed. In 1980 the majority of cases of active disease occurred among elderly nonaboriginal peopl