Active and passive screening for tuberculosis in Vaud Canton, Switzerland

This retrospective study compared the bacteriological and clinical presentation of tuberculosis and the outcome of treatment in immigrants notified for TB after active screening by chest X-ray at the border with other patients detected by passive screening.

Retrospective study of all patients notified for TB in Vaud Canton in 2001 and 2002.

In Vaud Canton 78% of the 179 patients notified for TB were foreign-born. Among 71 asylum seekers actively screened at the border, 49.3% [CI 37.4-61.2] were symptom-free vs 17.6% [CI 10.3-24.9] among 108 passively screened patients. In the passively screened group, the proportion of asymptomatic patients was 15.4% for Swiss patients, 8.6% for foreign workers, and 29.4% for other foreigners. The average duration of symptoms before diagnosis among patients with complaints was 2 months in actively screened foreign-born, compared to 2.5 months in passively screened patients (no significant difference by Wilcoxon-Mann-Whitney test). The proportion of pulmonary TB cases with positive smear or culture was 63.4% in actively screened patients vs 70.4% in passively detected cases. Among actively screened patients with bacteriological confirmation, 42.2% [CI 27.2-57.2] were asymptomatic compared to 13% [CI 5.31-20.7] for passively screened patients. Considering only smear positive patients, the proportion of symptom-free patients was 22.2% [CI 9.6-34.8] in 45 actively screened cases vs 11.7% [4.4-19.0] for 77 passive screening. Cure and treatment completion rate for new cases reached 88% for foreign workers, 83% for asylum seekers, 85% for Swiss patients, and 78% for other foreigners.

Actively screened patients were more frequently asymptomatic than passively detected cases, even when considering only patients with bacteriological confirmation. The active screening by chest X-ray of an immigrant population with a high prevalence of tuberculosis allows the early detection and treatment of tuberculosis. This may contribute to the protection of the resident population from infection. The outcome of treatment for tuberculosis was satisfactory in all population groups.