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Clinical Observation
October 8, 2001

Transmission of Mycobacterium tuberculosis Through Casual Contact With an Infectious Case

Author Affiliations

From the Departments of Epidemiology (Mr Golub, Drs Obasanjo and Chaisson, and Ms Pope) and International Health (Drs Bishai and Chaisson), The Johns Hopkins University School of Public Health, Baltimore, Md; Maryland Department of Health and Mental Hygiene, Baltimore (Mr Golub and Dr Cronin); and Departments of Medicine (Drs Sterling, Bishai, and Chaisson) and Pathology (Ms Harrington), The Johns Hopkins University School of Medicine, Baltimore; and Baltimore City Health Department (Mr Coggin; Mss Moore, Pope, and Thompson; and Drs Sterling and Chaisson).

Arch Intern Med. 2001;161(18):2254-2258. doi:10.1001/archinte.161.18.2254

Background  An ongoing restriction fragment length polymorphism study of Mycobacterium tuberculosis isolates from tuberculosis cases showed an identical 12-band IS6110 pattern unique to 3 unrelated patients (Patients A-C) diagnosed as having tuberculosis within a 9-month period.

Methods  In an attempt to identify epidemiologic links between the 3 patients, we performed site visits to the retail business work site of patient A and conducted detailed interviews with all 3 patients and their contacts.

Results  Patient B had visited patient A's work site 3 times during patient A's infectious period, spending no more than 15 minutes each time. Patient C visited patient A's work site on 6 to 10 occasions during this period for no more than 45 minutes at any one time. There were no other epidemiologic links between these 3 cases other than the contact at the store. Contact investigation identified 4 tuberculin skin test conversions among 8 (50%) of patient A's coworkers, 6 positive tests among 15 household contacts (40%), and 8 positive tests among 16 identified customers who were casual contacts (50%). Patient B and patient C were most likely infected by patient A during one of their brief visits to patient A's work site.

Conclusions  These data demonstrate that some tuberculosis is spread through casual contact not normally pursued in traditional contact investigations and that, in certain situations, M tuberculosis can be transmitted despite minimal duration of exposure. In addition, this outbreak emphasizes the importance of DNA fingerprinting data for identifying unusual transmission in unexpected settings.