Advanced Survey of Tuberculosis Transmission in a Complex Socioepidemiologic Scenario with a High Proportion of Cases in Immigrants

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Abstract
Background. An increase in the incidence of tuberculosis (TB) in immigrants has changed the socioepidemiologic scenario in Spain. It is generally assumed that TB in immigrants is the result of importation of infection, but the role of recent transmission is rarely considered. Standard contact tracing is not suitable for the survey of transmission in this complex scenario. Methods. During the study period (2003–2006), we genotyped 356 (90.4%) of 394 isolates from patients with microbiologically confirmed TB in Almería, the province with the highest percentage of TB cases among immigrants in Spain. The epidemiologic survey of TB transmission was performed by active data collection using standardized interviews of the patients with TB and subsequent interviews of the clustered patients (who were clustered on the basis of the restriction fragment–length polymorphism types of their isolates) to identify transmission locations (supported by nominal and/or photographic recognition by the clustered patients). Results. Of all 356 genotyped isolates, 131 (36.8%) were clustered, suggesting recent transmission. The difference between the clustering rate for immigrants (32.8%) and that for native patients (41.6%) was not statistically significant (P=.087); of the 45 clusters, 15 (33.3%) involved only immigrants, 17 (37.8%) involved only autochthonous patients, and 13 (28.9%) involved both immigrants and autochthonous patients. The advanced system to investigate the clustered patients succeeded in detecting links in 10 of the 12 clusters that involved >4 patients, whereas the conventional approach, based on contact tracing, could detect links in only 2 clusters. Conclusions. Recent transmission among immigrants and transmission permeability between the immigrant and autochthonous populations were found. Epidemiologic strategies that combine universal genotyping and refined surveys of the clustered patients are needed to investigate transmission patterns in complex scenarios.