Molecular Epidemiology of Tuberculosis in the Netherlands: A Nationwide Study from 1993 through 1997

Abstract

To disclose risk factors for active tuberculosis transmission in the Netherlands, restriction fragment length polymorphism (RFLP) patterns of 78% of the Mycobacterium tuberculosis isolates, from the period 1993–1997, were analyzed. 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; taking this into account, fewer cases were clustered than has been reported in other studies. Contact investigations in the five largest clusters of 23–47 patients suggested epidemiological linkage between cases. Of patients identified 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 Netherlands. Human immunodeficiency virus infection was not an independent risk factor for active transmission. Isoniazid-resistant strains were relatively less frequently clustered, suggesting that these generated fewer secondary cases.