Objective: To study clustered Mycobacterium tuberculosis isolates as an indicator of recent TB transmission in a small urban setting in Italy, and to determine associated risk factors.
Methods: M. tuberculosis strains isolated between 1991 and 1997 were characterised by IS6110 restriction fragment length polymorphism (RFLP) analysis.
Results: One hundred and ninety-five isolates were available for RFLP analysis, which revealed 163 different patterns. Available cases were represented by 137 Italians (70%), 32 Senegalese (17%), and 26 other foreign-born cases (13%). A unique fingerprint pattern was found in 143 cases (73.3%), while 52 strains (26.7%) were grouped into 20 clusters. Nineteen cases (10%) were resident in the same quarter of Brescia with a high density of Senegalese immigrants (Area A). An increased probability of yielding clustered M. tuberculosis strains was associated with residence in Area A (OR 3.87, 95%CI 1.42-10.56; P = 0.02) and being Senegalese (OR = 5.96, 95%CI 1.48-23.97; P = 0.005). In the logistic regression analysis, being Senegalese was independently associated with yielding a clustered M. tuberculosis strain.
Conclusions: Our results demonstrate a clustering of TB cases among Senegalese immigrants and suggest that RFLP analysis may be used to identify geographical areas where efforts can be targeted to interrupt TB transmission.