Setting: Culture-positive cases of tuberculosis (TB) from the urban population of southern Madrid and from all the prisons located throughout the city.
Objective: To determine the frequency with which common strains of Mycobacterium tuberculosis cause disease among patients from both the urban and prison populations of a large Spanish city.
Design: Restriction fragment length polymorphism analysis was performed on culture-positive cases of TB identified between 1 January 1997 and 31 December 1998. Risk factors that might be associated with the dissemination of common strains of TB among the two populations were also investigated.
Results: Two hundred and twenty-one cases of culture-positive TB were identified, 99 (47.8%) of which were grouped in 23 clusters. Eleven were general clusters that spanned the prison and urban populations involved 69 patients (31.2%). Univariate analysis of risk factors showed that age <35 years, human immunodeficiency virus (HIV) infection, intravenous drug use and current or previous imprisonment were all associated at a statistically significant level with inclusion in general clusters. The final logistic regression model showed an interaction between HIV infection and incarceration.
Conclusions: Dissemination of common strains of M. tuberculosis between prison inmates and the urban population of Madrid is significant, and involves subjects with a history of imprisonment and HIV infection.