Sandra V. Kik, from the KNCV Tuberculosis Foundation in The Hague, the Netherlands, and colleagues retrospectively identified 5,454 "clustered" cases of tuberculosis (recent transmission and rapid progression to disease from recent infection) in the Netherlands from 1993 to 2004 based on DNA fingerprint data, of which 1,756 (32 percent) were part of a cluster episode of two years (all cases with the same DNA fingerprint occurring within two years of the first diagnosed case with that fingerprint).

The researchers found that of 622 cluster episodes, 9 percent were large (five or more cases) and 91 percent were small episodes (two to four cases). Large cluster episodes were more likely if there had been less than three months between the diagnosis of the first two patients, one or both patients were younger than 35 years old, both patients lived in an urban area, and both patients were from sub-Saharan Africa.

"The retrospective study's main finding -- that large clusters can be predicted based on the characteristics of the first two cases -- adds new knowledge to our understanding of the transmission of M. tuberculosis and provides a practical tool for public health programs," Kathryn DeRiemer, Ph.D., from the University of California Davis, and Bouke de Jong, M.D., from New York University, write in an accompanying editorial.

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Prepared jointly by the editors of RN and HealthDay's Physicians' Briefing (www.physiciansbriefing.com).