The molecular epidemiology of tuberculosis in Zaragoza, Spain: a retrospective epidemiological study in 1993

The incidence of tuberculosis (TB) in Spain is one of the highest in Europe. In Zaragoza region the incidence rate of tuberculosis and the acquired immune deficiency syndrome (AIDS) are close to the national average.

To better define the molecular epidemiology of tuberculosis in an area of Europe where this has not been previously studied.

A retrospective epidemiological study on tuberculosis was conducted in Zaragoza, a region of Spain, in 1993. The study population consisted of 226 patients from whom positive culture and complete clinical and demographic data were available. Mycobacterium tuberculosis strains were typed by standard restriction fragment length polymorphism (RFLP). A cluster was defined as two or more isolates with identical RFLP patterns when five or more copies of IS6110 are present. The 137 non-clustered patients were compared with the 89 clustered patients and studied by using univariate analysis.

Thirty-nine percent of the patients were clustered, suggesting possible recent transmission. Infection with drug-resistant M. tuberculosis was associated with a decreased risk of being in a cluster. The strains isolated from human immunodeficiency virus (HIV)-positive patients were not associated with clustering. We found that immigration was not a major determinant in the total number of TB cases.

Immigration, HIV and drug resistance were not associated with recent transmission. More than 50% of the clusters contained two or three patients, indicating that small outbreaks were responsible for most of the tuberculosis cases. Our RFLP typing results indicate that a TB control programme should be implemented in Spain in order to lower transmission of TB.