A preventable outbreak of tuberculosis investigated through an intricate social network.

In 1998, a city in Indiana reported 4-fold increase in the number of cases of tuberculosis (TB). An investigation to assess the increase in cases and to identify possible epidemiologic links among persons with TB identified 41 cases of active TB. Epidemiologic links and/or matching DNA fingerprints were identified for 31 patients (76%). The majority of these patients were members of a single social network within the community. Links for most of these patients were identified after multiple interviews with patients and their contacts. TB control activities in the county were limited prior to the identification of the outbreak. At least 24 cases may have been preventable. This outbreak may have been prevented with prompt case identification and effective contact tracing and screening during the years before the outbreak. The use of social networks should be considered in the investigation of outbreaks that involve difficult-to-reach populations. TB control measures should be maintained in areas with historically low TB incidence.