DNA restriction fragment analysis to define an extended cluster of tuberculosis in homeless men and their associates.

A cluster of tuberculosis in men associated with shelters for the homeless in Melbourne, diagnosed between April 1984 and July 1991, was reviewed with respect to the genetic relatedness of the infecting strains. Relatedness was determined by examination of Southern blot analyses of restriction enzyme-digested genomic DNA, using probes for repetitive sequences. From the initial 24 cases selected, isolates were available from 19, and 18 were identical. A total of 571 other Australian and Solomon Islands strains were examined for relatedness to these strains. Nine additional case strains were found to be identical; all were from recent Melbourne residents and at least 7 were epidemiologically related to the original case cluster. The identification of a single infecting strain of Mycobacterium tuberculosis in these 27 cases suggests that reactivation disease in this group may not be as important as infection or reinfection from another case or cases.