Interrupting Transmission of Tuberculosis Key to Containing Global Epidemic

Findings recently published in The New England Journal of Medicine suggest increasing focus on interruption of transmission, rather than inadequate treatment of multidrug resistant (MDR) tuberculosis, not just in healthcare settings but also within social networks, is paramount to curtailing this worldwide epidemic and succession of extensively drug-resistant (XDR) tuberculosis.¹

KwaZulu-Natal, population 10.3 million, was identified by the South African government as having the highest rates of tuberculosis (1076 cases per 100,000 population) and HIV infection (prevalence, 16.9%) in South Africa. This gave a team funded by the National Institute of Allergy and Infectious Disease (NIAID) and others, a demographic area of approximately 94,361 square kilometers – roughly the size of Portugal – in which to study primary networks of participants newly diagnosed with XDR tuberculosis from May 2011 to August 2014 in rural and urban areas.

Each home of the 404 study participants was given a GPS coordinate as were 53 hospitals where patients were admitted before or after their diagnosis, however, diagnoses were made across the region at 212 healthcare facilities located across all 11 districts of KwaZulu-Natal.  A person-to-person link was identified in 59 participants who formed 25 social networks.  Social networks of note were found to include networks of multiple family homes, workplaces in common, churches, bars, nightclubs, prisons, beauty salons, restaurants and various other areas of social contact named by participants to identify significant pathways of transmission.

The use of multiple genotyping methods in combination with network and epidemiologic analysis as used in this study was proven to be an effective method for exposing transmission as the primary driver in XDR tuberculosis across the region, rather than inadequate treatment of acquired resistant MDR tuberculosis, as is the common assumption. 

In this study, acquired resistance MDR tuberculosis accounted for only 31% of the cases of XDR tuberculosis. The incidence of XDR tuberculosis in South Africa (2.8 cases per 100,000 population) is on par with the incidence of all forms of tuberculosis in the United States.²

The study investigators state limitations of the study include the inability to enroll all participants with XDR tuberculosis because of large case numbers during the study period, limited use of culture and drug-susceptibility testing, and an underestimation of transmission links between patients not enrolled in the study and study participants. Despite these limitations, the methodology and results successfully identified 30% of enrolled patients who formed an epidemiologic cluster.

References

1. Shah NS, Auld SC, Brust JC, et al. Transmission of extensively drug-resistant tuberculosis in South Africa. N Engl J Med. 2017;376:243-253. doi:10.1056/NEJMoa1604544.
2. Salinas JL, Mindra G, Haddad MB, Pratt R, Price SF, Langer AJ. Leveling of tuberculosis incidence – United States, 2013-2015. MMWR Morb Mortal Wkly Rep. 2016;65:273-278. doi:10.15585/mmwr.mm6511a2