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.