LARGE-SCALE DNA-FINGERPRINTING OF MYCOBACTERIUM-TUBERCULOSIS STRAINS AS A TOOL FOR EPIDEMIOLOGIC STUDIES OF TUBERCULOSIS

We conducted a large-scale DNA fingerprinting analysis of Mycobacteriu m tuberculosis strains in a country in which tuberculosis is endemic ( Tunisia) in order to evaluate the importance of microepidemics in the maintenance of the disease within the population. The genetic polymorp hisms of 201 strains of M. tuberculosis isolated from 196 unrelated pa tients living in four districts of northern Tunisia during a 3-year pe riod were studied by restriction fragment length polymorphism (RFLP) a nalysis by using the insertion sequence IS6110 as a probe. Seventy-thr ee strains isolated from 68 patients living in the districts of Tunis, Nabeul, and Jendouba generated 67 different RFLPs, indicating a high degree of polymorphism of the M. tuberculosis strains within these are as. In contrast, the 128 strains isolated from individuals in the dist rict of Menzel Bourguiba appeared much less heterogeneous since they o ften generated identical or very similar fingerprints. Seventeen of 29 cases (58%) of active tuberculosis in the city of Menzel Bourguiba co uld be traced to as few as four M. tuberculosis strains. These results indicate the persistence of underestimated microepidentics in this re gion. The RFLP typing of a large number of randomly collected strains provides a general picture of the strains involved in tuberculosis. Th e systematic study of limited areas where tuberculosis is endemic can provide evidence for the existence of persisting epidemics. This stres ses the different problems which remain to be solved in order to impro ve the control of tuberculosis.