THE MOLECULAR EPIDEMIOLOGY OF TUBERCULOSIS IN ZARAGOZA, SPAIN - A RETROSPECTIVE EPIDEMIOLOGIC-STUDY IN 1993

SETTING: The incidence of tuberculosis (TB) in Spain is one of the hig hest in Europe. In Zaragoza region the incidence rate of tuberculosis and the acquired immune deficiency syndrome (AIDS) are close to the na tional average. OBJECTIVE: To better define the molecular epidemiology of tuberculosis in an area of Europe where this has not been previous ly studied. DESIGN: A retrospective epidemiological study on tuberculo sis was conducted in Zaragoza, a region of Spain, in 1993. The study p opulation consisted of 226 patients from whom positive culture and com plete clinical and demographic data were available. Mycobacterium tube rculosis strains were typed by standard restriction fragment length po lymorphism (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 p atients and studied by using univariate analysis. RESULTS: Thirty-nine percent of the patients were clustered, suggesting possible recent tr ansmission. Infection with drug-resistant M. tuberculosis was associat ed with a decreased risk of being in a cluster. The strains isolated f rom human immunodeficiency virus (HIV)-positive patients were not asso ciated with clustering. We found that immigration was not a major dete rminant in the total number of TB cases. CONCLUSION: 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 cas es. Our RFLP typing results indicate that a TB control programme shoul d be implemented in Spain in order to lower transmission of TB.