We conducted a population-based molecular epidemiological study of tuberculosis (TB) in Madrid, Spain (2002 to 2004), to define transmission patterns and factors associated with clustering. We particularly focused on examining how the increase in TB cases among immigrants in recent years (2.8% in 1997 to 1999 to 36.2% during the current study) was modifying transmission patterns. Mycobacterium tuberculosis isolates obtained from patients living in nine districts of Madrid (1,459,232 inhabitants) were genotyped. The TB case rate among foreign-born people was three to four times that of Spanish-born people, and the median time from arrival to the onset of treatment was 22.4 months. During the study period, 227 (36.3%) patients were grouped in 64 clusters, and 115 (50.7%) of them were in 21 clusters with mixed Spanish-born and foreign-born patients. Three of the 21 mixed clusters accounted for 21.1% of clustered patients. Twenty-two of 38 (57.9%) immigrants in mixed clusters were infected with TB strains that had already been identified in the native population in 1997 to 1999, including the three most prevalent strains. Factors identified as independent predictors of clustering were homelessness (odds ratio [OR], 2.3; 95% confidence interval [95% CI], 1.2 to 4.5; P ؍ 0.011) and to be born in Spain (OR, 1.8; 95% CI, 1.2 to 2.6; P ؍ 0.002). The results indicated that (i) TB transmission was higher in Spanish-born people, associated mainly with homelessness, (ii) that foreign-born people were much less likely to be clustered, suggesting a higher percentage of infection before arriving in Spain, and (iii) that an extensive transmission between Spanish-and foreign-born populations, caused mainly by autochthonous strains, was taking place in Madrid.
In recent years, the number of cases of tuberculosis (TB) among immigrants in Spain has increased markedly, and led to this analysis of the recent transmission patterns of TB in the immigrant population in Madrid. The countries from which the highest number of immigrant cases have been reported were Ecuador (21%), Romania (16%), Morocco (12%), Peru (11%) and Bolivia (9%). Fifty-one per cent of the cases were from South America. In a multicentre study (2004-2006), IS6110 restriction fragment length polymorphism and spoligotyping were used to genotype the Mycobacterium tuberculosis isolates from 632 immigrant cases from 47 countries. A total of 183 cases (29%) were grouped into 59 clusters, which are markers of potential transmission events. Most of the clusters (81%) included patients living in different healthcare districts, and 54% of the clusters were multinational. When a sample of 478 autochthonous cases was included, 53% of the clusters involving immigrants also included autochthonous cases. This study revealed marked transmission permeability among nationalities and between the immigrant and the autochthonous populations.
In this study, use of the capture-recapture technique allowed us to combine epidemiological information obtained by conventional and molecular methods to quantify the number of cases of recently transmitted TB in the community and identify specific populations at high risk of disease. This information is clearly important because such groups are a prime target for improved TB control measures. In the long term, this combination of techniques may contribute significantly to control the spread of TB.
The most prevalent strain of Mycobacterium tuberculosis in Madrid, Spain (strain 5) was recovered from 45 cases between 1997 and 2004 and showed a highly homogeneous genetic composition. This strain was not exclusive to Spain, and its spoligotyping signature (ST20) was found in entries from different countries in the SITVIT1 database. Patients infected with strain 5 were more frequently positive for human immunodeficiency virus and autochthonous, and had been in prison more frequently, but strain 5 did not show increased infectivity in an in-vitro model of infection.
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