# The Role of Community Networks in the Transmission and Persistence of M. tuberculosis in Urban Africa with Endemic Tuberculosis

## TL;DR

This study explores how community networks contribute to the spread of tuberculosis in urban Africa, finding that transmission often occurs through weak social ties and geographic hubs.

## Contribution

The study introduces a novel population-based framework to analyze M. tuberculosis transmission through community contact networks.

## Key findings

- Transmission often occurs among contacts with weak or distant ties to the index case.
- Geographic structural holes in the network may link cases with unknown contacts.
- Social networks alone are insufficient to explain the full pattern of tuberculosis transmission.

## Abstract

Tuberculosis persists today in many resource-limited countries in the southern hemisphere because unobserved transmission of M. tuberculosis occurs in undefined contact networks of infectious cases.

To study the transmission dynamics of M. tuberculosis in an African city with endemic tuberculosis, we built out a sociocentric network in the Lubaga Division of Kampala, Uganda, using the personal networks of 130 index cases and 123 community controls frequency-matched by age, sex, and parish. Clusters of genetically related strains were identified using whole genome sequencing was from 99 isolates of the cases. The social distance between cases with related pairs was estimated from the sociocentic network.

We found that characteristics of this sociocentric network account, in part, for tuberculosis persistence. These characteristics included highly connected network members, or hubs, where mixing among contacts may occur; predominant transmission among contacts with weak, or distant, ties to the index case; and geographic structural holes in the network that may link cases with these unknown contacts.

These findings suggest that active case finding within the social networks of index cases may result in marginal gains in reducing transmission of tuberculosis. To achieve greater gains, transmission in the community may be reduced through population-based strategies that disrupt transmission in geographic hubs of transmission where mixing may occur between infectious cases and community contacts.

This research was conducted with support from the National Institute of Health (AI093856, AI147319, P30 AI 68386, D43TW010045, D43TW012481).

The current study used a population-based, novel framework to identify patterns of M. tuberculosis transmission through community contact networks. We found that social networks are not sufficient to explain the extent or pattern of tuberculosis transmission in the community. The findings suggest that tuberculosis control interventions that focus on households alone or social networks identified by index cases may produce only marginal gains in reducing the epidemic of tuberculosis.