Genotyping of Mycobacterium tuberculosis over two periods: a changing scenario for tuberculosis transmission

To evaluate changes in the molecular epidemiology of tuberculosis (TB) in Zaragoza, Spain, over a decade that has seen large social and health changes, including the attenuation of the human immunodeficiency virus (HIV) epidemic and increased immigration.

A population-based molecular study was conducted using standard restriction fragment length polymorphism IS6110 typing that included all patients with bacteriologically confirmed TB living in the Zaragoza area from 2001 to 2004. The current situation was compared with that described in a previous study from 1993 to 1995.

A total of 454 Mycobacterium tuberculosis isolates were genotyped; 239 (52.6%) were grouped in 45 clusters composed of 2 to 85 isolates. Independent risk factors for clustering were identified. The main differences with the previous study were the increase of TB cases among immigrants, a decrease in HIV-TB co-infected patients and the occurrence of a large TB outbreak involving 85 patients (M. tuberculosis Zaragoza [MTZ] strain).

A change in the epidemiological pattern of TB has been observed in the last years. TB transmission is more common among the Spanish-born population, while foreign birth is significantly less associated with clustering. A single epidemic strain caused 18.7% of all TB cases.