Unsuspected recent transmission of tuberculosis among high-risk groups:: Implications of universal tuberculosis genotyping in its detection

Background. The initiation of universal genotyping revealed 3 clusters of 19 patients with tuberculosis ( TB) in Wisconsin, with no apparent epidemiologic links among most of them. An epidemiologic investigation was conducted to determine whether genotype clustering resulted from recent transmission. Methods. We conducted additional interviews with patients and reviewed medical records. Places frequented by the patients while they were infectious were visited to identify contacts. Results. Our investigation revealed several previously unrecognized possible sites of TB transmission: a single-room occupancy hotel, 2 homeless shelters, 1 bar, and 2 crack houses. Seven patients with previously diagnosed TB were added to the clusters. Of 26 patients, we identified epidemiologic links for all but 1. Common risk factors among patients included alcohol abuse, crack cocaine use, homelessness, and unemployment. Additionally, 98 contacts missed during routine contact investigation were identified. Conclusions. Transmission of TB, particularly among high-risk groups, may go undetected for years. Our investigation demonstrated the value of universal genotyping in revealing unsuspected recent TB transmission and previously unrecognized sites of transmission, which can be targeted for specific TB interventions.