Tuberculosis from transmission in clinics in high HIV settings may be far higher than contact data suggest

Abstract

Background: In South Africa, it is estimated that only 0.5-6% of people’s contacts occur in clinics. Both people with infectious tuberculosis and people with increased susceptibility to disease progression may spend more time in clinics however, increasing the importance of clinic-based transmission to overall disease incidence.

Methods: We developed an illustrative mathematical model of Mycobacterium tuberculosis transmission in clinics and other settings. We assumed that 1% of contact time occurs in clinics. We varied the ratio of clinic contact time of HIV positive people compared to HIV negative people, and of people with infectious tuberculosis compared to people without tuberculosis, while keeping the overall proportion of contact time occurring in clinics, and each person’s total contact time, constant.

Results: With clinic contact rates 10 and 5 times higher in HIV positive people and people with tuberculosis respectively, 10.7% (plausible range: 8.5%-13.4%) of tuberculosis resulted from transmission in clinics. With contact rates in HIV positive people and people with tuberculosis 5 and 2 times higher respectively, 5.3% (4.3%-6.3%) of all tuberculosis was due to transmission in clinics.

Conclusion: The small amounts of contact time that occur in clinics may greatly underestimate their contribution to tuberculosis disease in high tuberculosis/HIV burden settings.