MOLECULAR AND GEOGRAPHIC PATTERNS OF TUBERCULOSIS TRANSMISSION AFTER 15 YEARS OF DIRECTLY OBSERVED THERAPY

Context.-Recent studies suggest that one third of tuberculosis cases i n urban areas result from recent transmission. Improved tuberculosis c ontrol measures such as uniform implementation of directly observed th erapy might reduce the proportion of cases resulting from recent trans mission. Objective.-To determine patterns of tuberculosis transmission in Baltimore, Md, after 15 years of community-based directly observed therapy. Design.-A 30-month (January 1994-June 1996), prospective, ci ty-wide study of all cases of tuberculosis using traditional contact i nvestigations, geographic information systems data, and molecular epid emiologic comparison of Mycobacterium tuberculosis isolates with 2 DNA probes. Patients.-One hundred eighty-two patients with culture-positi ve tuberculosis. Main Outcome Measures.-Proportion of disease defined as recently transmitted based on epidemiologic linkage by traditional contact tracing and molecular, linkage by DNA fingerprint analysis of isolates; geographic foci of transmission based on linkage of residenc es by geographic information systems data. Results.-Of the 182 patient s who had isolates of M tuberculosis available, 84 (46%) showed molecu lar clustering with 58 (32%) defined as being recently transmitted. On ly 20 (24%) of 84 cases with clustered DNA fingerprints had epidemiolo gic evidence of recent contact. Geographic analysis showed significant spatial aggregation of the 20 clustered cases with epidemiologic link s (P<.001), occurring in areas of low socioeconomic status and high dr ug use, The 64 cases with clustered DNA fingerprints but without epide miologic links shared common risk factors and demographic features wit h the 20 clustered patients who did have epidemiologic links. Conclusi ons.-Recently transmitted tuberculosis accounts for a high proportion of tuberculosis cases in Baltimore. Recently transmitted cases occur i n geographically distinct areas of Baltimore, and location-based contr ol efforts may be more effective than contact tracing for the early id entification of cases.