Risk factors for developing tuberculosis: a 12-year follow-up of contacts of tuberculosis cases.

Background: Many risk factors for the development of tuberculosis (TB) have been reported but have not been simultaneously assessed.
Objective: To determine the risk of developing TB associated with each risk factor, after adjusting for all others.
Methods: We performed a population-based, retrospective cohort study of the contacts of TB cases recorded in British Columbia, Canada. Known risk factors for the development of TB were assessed over a 12-year period; Cox regression was used to estimate the hazard ratios (HRs) of TB, adjusting for the other factors.
Results: Among 33 146 TB contacts, 228 developed TB during the study period (TB rate 668 per 100,000 population, 95%CI 604-783). The main risk factors for TB development were malnutrition (HR 37.5), no treatment of latent TB infection (HR 25) or <6 months of treatment (HR 5.38), age 0-10 years (HR 7.87), being a household contact (HR 8.47) and having a tuberculin skin test induration of >or=5 mm (HR >or=4.99). Bacille Calmette-Guérin vaccination significantly reduced the risk of TB development (HR 0.32, 95%CI 0.20-0.50).
Conclusions: Among contacts of TB cases, we have identified the few factors that carry a very high risk for developing TB. These factors identify populations at highest risk and permit more effective TB control.