Extrapulmonary tuberculosis: epidemiology and risk factors

Abstract

Objective: To describe the epidemiology and risk factors associated with extra-pulmonary tuberculosis (EPTB).

Method: Cases of tuberculosis (TB) diagnosed from 1991 to 2008 in a Caucasian population were classified as EPTB or pulmonary TB (PTB). Of all cases, 63.7% were followed up in a specialist TB unit. A standardised protocol for data collection was used, including: gender, age, BCG vaccination, contact with PTB patient, smoking habit, alcohol abuse, diabetes mellitus, immunosuppressive drugs/steroids and HIV-status. These variables were compared between EPTB and PTB groups. Statistical analysis was based on logistic regression. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated.

Results: Among the 2,161 cases diagnosed, 1,186 were PTB and 705 EPTB. The overall TB incidence had fallen from 79.9/100,000 in 1992 to 27.1/100,000 in 2008, P<.05. The number of EPTB cases decreased more slowly than PTB. EPTB increased from 30.6% of cases in 1991-1996 to 37.6% in 2003-2008 (lymphatic site increased 27%), by trend test P<.05. At multivariate level, being female (OR 2.04; 95% CI: 1.56-2.66) and age (OR 1.02; 95% CI: 1.01-1.022) were associated with EPTB, while alcohol abuse (OR 0.33; 95% CI: 0.20-0.52), smoking habit (OR 0.45; 95%CI: 0.34-0.59), contact with PTB patients (OR 0.57; 95% CI: 0.44-0.76) and BCG vaccination (OR 0.64; 95% CI: 0.44-0.92) had a protective effect. The proportion of female gender and age of patients increased over time, whilst there was a decrease in BCG vaccinated patients.

Conclusions: Whilst there has been a reduction in the overall incidence of TB, the proportion of EPTB increased. The proportional increase in EPTB could be explained by an increase in life expectancy and the predominance of women in the population, and by a decline in BCG vaccinated patients.