Molecular epidemiology of tuberculosis in the Netherlands: A nationwide study from 1993 through 1997

To disclose risk factors for active tuberculosis transmission in the Nether lands, restriction fragment length polymorphism (RFLP) patterns of 78% of t he Mycobacterium tuberculosis isolates, from the period 1993-1997, were ana lyzed. Of the respective 4266 cases, 46% were found in clusters of isolates with identical RFLPs, and 35% were attributed to active transmission. The clustering percentage increased strongly with the number of isolates; takin g this into account, fewer cases were clustered than has been reported in o ther studies. Contact investigations in the five largest clusters of 23-47 patients suggested epidemiological linkage between cases, Of patients ident ified through contact tracing, 91% were clustered, Demographic risk factors for active transmission of tuberculosis included male sex, urban residence , Dutch and Surinamese nationality, and long-term residence in the Netherla nds, Human immunodeficiency virus infection was not an independent risk fac tor for active transmission, Isoniazid-resistant strains were relatively le ss frequently clustered, suggesting that these generated fewer secondary ca ses.