Impact of social interactions in the community on the transmission of tuberculosis in a high incidence area

Background-Tuberculosis (TB) is transmitted by close contact with an infect ious person. It is assumed that close contact occurs amongst household memb ers and that contact outside the house is "casual" and does not play a majo r role in the transmission of TB. Methods-This study was conducted in an impoverished area with a high incide nce of TB and a low! HIV seropositive prevalence. Thirty three households w ith 84 TB patients were identified between February 1993 and April 1996 and the transmission of TB was studied by combining Mycobacterium tuberculosis fingerprinting with in depth sociological interviews. Results-Forty two strain genotypes were identified in the 84 patients. In 1 5 households all the patients had identical strains, in nine households all the patients had different strains, and in nine households some patients h ad identical strains and one had a different strain. In 26 houses at least one patient had a strain which formed part of a larger community cluster an d in 12 of these households the patient(s) had contact with a community mem ber who had the identical strain. In 58% of the cases the contact took plac e while drinking in social groups. Conclusion-In high incidence areas contact outside the household may be imp ortant for the transmission of Tn. This contact often takes place during re creation which, in the case of this study of impoverished people, consisted of drinking in social groups. Social interaction patterns should be studie d and understood for effective implementation of control strategies.