Estimating the contribution of transmission in primary healthcare clinics to community-wide TB disease incidence, and the impact of infection prevention and control interventions, in KwaZulu-Natal, South Africa

Background There is a high risk of Mycobacterium tuberculosis (Mtb) transmission in healthcare facilities in high burden settings. Recent World Health Organization guidelines on tuberculosis infection prevention and control (IPC) recommend a range of measures to reduce transmission in healthcare and institutional settings. These were evaluated primarily based on evidence for their effects on transmission to healthcare workers in hospitals. To estimate the overall impact of IPC interventions, it is necessary to also consider their impact on overall community-wide tuberculosis incidence and mortality. Methods We developed an individual-based model of Mtb transmission between household members, in primary healthcare clinics (PHCs), and in other congregate settings; drug sensitive and multidrug resistant tuberculosis disease development and resolution; and HIV and antiretroviral therapy (ART) and their effects on tuberculosis. The model was parameterised using data from a high HIV prevalence, rural/peri-urban community in KwaZulu-Natal, South Africa, including data on social contact in clinics and other settings by sex, age group, and HIV/ART status; and data on the prevalence of tuberculosis in clinic attendees and the general population. We estimated the proportion of disease in adults that resulted from transmission in PHC clinics in 2019, and the impact of a range of IPC interventions in clinics on community-wide TB incidence and mortality. Results We estimate that 7.6% (plausible range 3.9-13.9%) of drug sensitive and multidrug resistant tuberculosis in adults resulted from transmission in PHC clinics in the study community in 2019. The proportion is higher in HIV-positive people, at 9.3% (4.8%-16.8%), compared to 5.3% (2.7%-10.1%) in HIV-negative people. We estimate that IPC interventions could reduce the number of incident TB cases in the community in 2021-2030 by 3.4-8.0%, and the number of deaths by 3.0-7.2%. Conclusions A non-trivial proportion of tuberculosis results from transmission in PHC clinics in the study communities, particularly in HIV-positive people. Implementing IPC interventions could lead to moderate reductions in disease burden. We therefore recommend that IPC measures in clinics should be implemented both for their benefits to staff and patients, but also for their likely effects on TB incidence and mortality in the surrounding community.