Molecular epidemiology study of exogenous reinfection in an area with a low incidence of tuberculosis

In geographical areas with a low incidence of tuberculosis, recurrent tuber culosis is generally due to reactivation of the disease. However, the relat ive contribution of tuberculosis reinfection increases in parallel with the incidence of disease and is likely to depend on the epidemiological contex t: factors such as the spread of multidrug resistance, human immunodeficien cy virus (HIV) infection, and immigration from developing countries could m odify disease transmission in areas at low risk for tuberculosis, A molecul ar epidemiology study was performed in Lombardy, Northern Italy, where the incidence of tuberculosis is 17.5 cases per 100,000 persons. A total of 2,4 52 cases of culture-confirmed tuberculosis in 2,127 patients were studied. A group of 32 patients (1.5%), each of whom had two episodes of tuberculosi s with cure as the outcome of the first episode and with more than 6 months between the two episodes, were studied by means of restriction fragment le ngth polymorphism DNA fingerprinting analysis, For 5 of the 32 patients (16 %), the DNA fingerprinting patterns of Mycobacterium tuberculosis strains r esponsible for the second episode did not match those of the corresponding isolates of the first episode, indicating exogenous reinfection. Two of the se patients developed multidrug-resistant tuberculosis during the second ep isode, and in three cases the isolates belonged to clusters of M. tuberculo sis strains spreading in the community. A fourfold-increased risk for reinf ection was observed in immigrant patients compared to Italian subjects. In contrast, a higher risk of relapse rather than reinfection was evidenced in HIV-positive subjects and in patients infected with multidrug-resistant tu berculosis. Episodes of tuberculosis reinfection in areas with a low incide nce of tuberculosis are rare compared to those in high-incidence geographic al regions, In populations that have immigrated from high-risk areas, reinf ection may represent a considerable contributor to the rate of recurrent tu berculosis, This finding emphasizes the importance of containing the spread of epidemic strains in close communities, in order to prevent changes in g lobal tuberculosis trends for developed countries.