The large worksite tuberculosis exposure: devising a functional risk model

In March 2007, an employee at a large Oregon call center was diagnosed with active tuberculosis (TB), prompting a worksite investigation to assess transmission among more than 1,500 employees. We sought to determine the number of new TB infections linked to the index case and to evaluate infection risk by proximity and duration of exposure. Current and former employees from October 2006 to March 2007 were encouraged to undergo TST or QFT‑G testing and complete questionnaires on exposure and risk factors. Of 531 employees fully evaluated, 65 (12%) had new latent TB infection, and three secondary active cases were identified. Employees seated within 25 feet of the index case had significantly higher infection prevalence (41%; RR = 3.1), and those exposed for more than 60 days also had elevated risk (17%; RR = 2.5). Combined exposure measures demonstrated a clear dose‑response pattern. Findings indicate that proximity and exposure duration are critical factors in assessing TB transmission risk in large open‑workspace environments and can guide prioritization during large‑scale contact investigations.