Spread of Mycobacterium tuberculosis in a community implementing recommended elements of tuberculosis control

Context Despite improvements in tuberculosis (TB) control during the past d ecade, Mycobacterium tuberculosis transmission and resulting disease contin ue to occur in the United States. Objective To determine the primary reasons for disease development from a p articular strain of M tuberculosis. Design Population-based, molecular epidemiological study. Setting Urban community in the San Francisco Bay area of California with re commended elements of TB control in place. Patients Seventy-three TB cases were reported in 1996-1997 that resulted fr om 1 strain of M tuberculosis as identified by TB genotyping and epidemiolo gical linkage. Main Outcome Measures Transmission patterns involving source and secondary case-patients; primary reasons for disease development. Results Seventy-three (33%) of 221 TB case-patients in this community resul ted from this strain of M tuberculosis. Thirty-nine (53%) of the 73 case-pa tients developed TB because they were not identified as contacts of source case-patients; 20 case-patients (27%) developed TB because of delayed diagn osis of their sources; and 13 case-patients (18%) developed TB because of p roblems associated with the evaluation or treatment of contacts; and 1 case -patient (1%) developed TB because of delay in being elicited as a contact. Of the 51 TB cases identified with sources, 49 (96%) were infected within the 2 years prior to diagnosis. Conclusions Our results indicate that in a community that has implemented t he essential elements of TB control, TB from ongoing transmission of M tube rculosis will continue to develop unless patients are diagnosed earlier and contacts are more completely identified.