Modelling the effect of infection prevention and control measures on rate of Mycobacterium tuberculosis transmission to clinic attendees in primary health clinics in South Africa

Abstract

Background: Elevated rates of tuberculosis in healthcare workers demonstrate the high rate of Mycobacterium tuberculosis (Mtb) transmission in health facilities in high-burden settings. In the context of a project taking a whole systems approach to tuberculosis infection prevention and control (IPC), we aimed to evaluate the potential impact of conventional and novel IPC measures on Mtb transmission to patients and other clinic attendees.

Methods: An individual-based model of patient movements through clinics, ventilation in waiting areas, and Mtb transmission was developed, and parameterised using empirical data from eight clinics in two provinces in South Africa. Seven interventions-codeveloped with health professionals and policy-makers-were simulated: (1) queue management systems with outdoor waiting areas, (2) ultraviolet germicidal irradiation (UVGI) systems, (3) appointment systems, (4) opening windows and doors, (5) surgical mask wearing by clinic attendees, (6) simple clinic retrofits and (7) increased coverage of long antiretroviral therapy prescriptions and community medicine collection points through the Central Chronic Medicine Dispensing and Distribution (CCMDD) service.

Results: In the model, (1) outdoor waiting areas reduced the transmission to clinic attendees by 83% (IQR 76%-88%), (2) UVGI by 77% (IQR 64%-85%), (3) appointment systems by 62% (IQR 45%-75%), (4) opening windows and doors by 55% (IQR 25%-72%), (5) masks by 47% (IQR 42%-50%), (6) clinic retrofits by 45% (IQR 16%-64%) and (7) increasing the coverage of CCMDD by 22% (IQR 12%-32%).

Conclusions: The majority of the interventions achieved median reductions in the rate of transmission to clinic attendees of at least 45%, meaning that a range of highly effective intervention options are available, that can be tailored to the local context. Measures that are not traditionally considered to be IPC interventions, such as appointment systems, may be as effective as more traditional IPC measures, such as mask wearing.

Keywords: health systems; mathematical modelling; tuberculosis.

Figure 1

Example illustration of the movement of two hypothetical patients through a clinic in the model. The blue and green shadings indicate different waiting areas.

Figure 2

Estimated reduction in the rate of Mycobacterium tuberculosis transmission to patients in clinics, by province and intervention. The central line indicates the median, the box range the IQR, the whiskers the most extreme value within 1.5 * IQR from the box, and the points outlying values. In the queue management intervention in KwaZulu-Natal, 1.3% of points were below −20%, with a minimum of −162%. In the appointment system intervention in KwaZulu-Natal, 1.3% of points were below −20%, with a minimum of −83%. These points are not shown on the graph. The appointment system intervention was not modelled in Western Cape, due to the presence of existing appointment systems. CCMDD, Central Chronic Medicine Dispensing and Distribution; UVGI, ultraviolet germicidal irradiation.

Figure 3

Number of patients in the clinic over time in the baseline, appointments, and CCMDD interventions, and the mean rate of transmission to each patient in the clinic over time in all scenarios, for clinic 1. The black line shows the median result, the dark red band the IQR and the light red band the 95% plausible range. For interventions where a plot of the number of patients over time is not shown, the intervention has no effect on patient numbers. Transmission rates are relative to the highest transmission rate in any scenario at any point in time. Figures for the other clinics are shown in the supplemental material. CCMDD, Central Chronic Medicine Dispensing and Distribution; UVGI, ultraviolet germicidal irradiation.