Local social contact patterns shape tuberculosis control effectiveness

Tuberculosis transmission is influenced by a mix of social, environmental and biological factors, including the number of people someone meets and how long they spend together indoors. Kate E LeGrand and colleagues point out that data on these social contacts can reveal likely transmission patterns, but that such data are often only used in mathematical modelling and not more broadly in public health planning. To explore how contact patterns could inform prevention and care, the researchers collected social contact information in three South African communities of similar size: an urban township, a peri-urban clinic catchment area, and a rural clinic catchment area. Participants were asked about the congregate settings they visited over a 24-hour period, how long they spent there, and their estimates of how many people were present. The team used that information to estimate where contact hours—time spent in proximity to others—occurred: inside the home, in congregate settings outside the home, and outside the participants’ own communities. This approach was designed to highlight three decision points for TB control: household contact tracing, infection prevention and control in communal spaces, and contamination risks in cluster trials.

The survey measured total contact hours and how those hours were distributed across places people spend time. On average participants reported 27.0 contact hours in the rural community, 55.2 in the peri-urban area, and 73.0 in the urban township. A large share of contact hours in the rural and peri-urban communities took place inside the home: 76.8% and 71.7% respectively, compared with 48.6% in the urban community. Where people spent their non-household contact time also differed by setting. Urban participants spent the largest share of contact hours in retail and office settings (19.9%), peri-urban participants in community-service buildings (20.4%), and rural participants in other people’s homes (25.5%). Movement beyond the local community was highest in the urban group, with 67.0% of contact hours occurring outside the participant’s community, compared with 38.8% in the rural area and 21.5% in the peri-urban area. These patterns were estimated from participants’ reports of places visited, visit durations, and numbers of people present over a single day.

These differences in social contact patterns have direct implications for tuberculosis prevention, detection, and research design. Where household contact hours are highest—such as the rural community in this study—household contact tracing is likely to find more exposed people and could be a particularly efficient way to identify and treat infections. In settings where people mix more in varied public or communal spaces, prioritising infection prevention and control (IPC) measures in the specific congregate locations most visited may increase overall impact. The finding that urban participants spent a large share of contact hours outside their home and outside their community also matters for planning outreach and for understanding how infections can spread across neighborhoods. For cluster randomised trials, knowing local contact patterns can help design clusters to reduce contamination between study arms. Overall, the work suggests that using simple social contact surveys to map where and how people spend time together can help tailor TB interventions to local realities and make prevention and care more effective.