Abstract:

Objective: To understand factors associated with discrepancy between interferon-γ release assay (IGRA) and Tuberculin Mantoux test (TST), and effect of preventive treatment in preventing tuberculosis incidence among prisoners. Methods: A community-based randomized controlled trail was conducted by selecting five prisons in a city, and allocating separate wards into intervention group and control group in each prison. The control group enrolled 981 participants, who underwent routine Tuberculosis control strategy; the intervention group enrolled 981 participants, who were tested for latent tuberculosis infection (LTBI) using IGRA and TST on the basis of routine tuberculosis control strategy, and the IGRA positive ones were provided preventive treatment under informed consent. All participants were interviewed for epidemiological information, and underwent regular chest X-ray examination every year. We analyzed factors associated with the discrepancy between results of IGRA and TST, and compared tuberculosis incidence in the following three years between the two groups. Results: The consistency between IGRA and TST was 77.93% (745/956). BCG scar (OR=1.477, 95%CI: 1.068-2.043) was associated with the discrepancy between the two testing methods. In the three years’ follow-up, tuberculosis incidence was 0% (0/157) among 157 IGRA positive participants who accepted and all completed preventive anti-tuberculosis treatment, and 2.05% (7/342) among those who did not take preventive treatment (χ²=3.259, P=0.071); the tuberculosis incidence was 0% (0/460) among IGRA negative participants, significantly lower than 2.05% (7/342) among the IGRA positive ones who didn’t take preventive treatment (χ²=9.498, P=0.002); overall, tuberculosis incidence was 0.71% (7/981) in the intervention group and 1.22% (12/981) in control group (χ²=1.329, P=0.249). Conclusion: Among prisoners, BCG vaccination is the key factor associated with the discrepancy between IGRA and TST; LTBI testing using IGRA followed by preventive treatment to the positive ones is an effective way to reduce tuberculosis incidence in prisons.

Key words: Mycobacterium tuberculosis, Tuberculin test, Prison, Diagnosis, differential