Reducing Ongoing Transmission of Tuberculosis

Restriction fragment length polymorphism (RFLP) analysis to identify specific Mycobacterium tuberculosis strains, in combination with epidemiologic investigation, has shattered old dogmas and yielded new insights into the transmission dynamics of tuberculosis. In several cities in the United States, RFLP studies and epidemiologic analysis have shown that 19% to 54% of tuberculosis cases probably result from recent infection. 1-4 Effective tuberculosis control measures should reduce this percentage. Yet, in this issue of THE JOURNAL, Bishai and colleagues 5 suggest that recent transmission accounted for 32% of tuberculosis cases in Baltimore, Md, where an excellent tuberculosis control program has used community-based directly observed therapy (DOT) since 1981. How can these results be explained? First, during the 5 years preceding the study period, 33% of patients diagnosed as having tuberculosis in Baltimore were not in the DOT program, 6 and suboptimal therapy for these patients may have contributed to continued disease transmission. Second, limiting transmission of tuberculosis requires a multifaceted program that includes timely identification of cases, isolation of contagious cases, aggressive contact investigation, and preventive therapy for persons infected with M tuberculosis .I t is difficult to assess these aspects of a tuberculosis control program, and suboptimal performance in these areas also may have contributed to ongoing tuberculosis transmission.