It has been estimated that 1.7 billion people have tuberculosis (TB) infection; yet current tests are unable to predict which people are at highest risk of developing TB disease, which can be life-threatening. THWART-TB is a prospective longitudinal cohort study of health workers (HWs) in Cape Town, South Africa, where our preliminary data reveals HWs have a high annual TB infection risk (34%). This cohort, who will undergo frequent serial evaluation (every 3 months) with a combination of novel assays never previously evaluated together, presents a unique opportunity to evaluate immune responses at the time of initial infection and to characterize the dynamic profile of these immune responses over time in a high-risk population. The knowledge generated will improve our understanding of TB infection and help to identify which people exposed to TB may remain at risk, enabling us to better target preventive strategies.

Tuberculosis (TB) remains a leading infectious cause of death in South Africa and globally.1.7 billion people worldwide are estimated to have been infected with TB (LTBI). However, current LTBI tests cannot distinguish between current infection versus a persistent immune response to a cleared infection and have a low predictive value to identify which people are at future risk of developing active TB disease. Moreover, LTBI following exposure to Mycobacterium tuberculosis (Mtb) is not a steady state process. The dynamic host-pathogen interactions that lead to bacterial clearance, suppression, or disease are not understood. The investigators propose to establish a prospective longitudinal cohort study of health workers (HWs) in Cape Town, South Africa, where previous data demonstrated HWs have a high annual TB infection risk (34%). Our fundamentally innovative approach will characterize early TB infection using serial testing every 3 months for one year with a combination of established and novel assays never previously evaluated together. This presents a unique opportunity to evaluate host and pathogen responses at the time of initial infection and to characterize the dynamic profile of these responses over time in a high-risk population, establishing a longitudinal platform for future studies, including through biobanked specimens. This study will generate critical data of local relevance given the devastating ongoing impact of TB in South Africa.

The investigators hypothesize that Mtb persistence or clearance in the first year after incident infection (determined by follow up interferon gamma release assay (IGRA) after a new IGRA conversion) correlates with dynamic changes in host blood transcriptional markers of incipient and active TB, Mtb antibody responses and Mtb DNA detection.

Aim 1: To evaluate the temporal dynamics of established and novel interferon-gamma based tests for latent TB infection. The investigators hypothesize high-frequency serial IGRA testing will enable us to identify how often sustained conversions and reversions occur after early TB infection (based on initial IGRA conversion) over 1 year follow up. The investigators will compare the performance of established and novel IGRAs and new LTBI tests.

Aim 2: To evaluate the temporal dynamics of host responses to TB based on RNA biosignatures and Mtb antibodies. The investigators hypothesize that sustained IGRA conversion may predict seroconversion and a contemporary rise in host-response blood transcriptional biomarkers of TB and will evaluate how these profiles change over time

Aim 3: To evaluate the temporal dynamics of novel assays to detect pathogen-directed Mtb DNA markers of early infection. The investigators hypothesize IGRA conversion, seroconversion, or rise in host-response blood transcriptional biomarkers of TB will predict detection of Mtb DNA using a range of novel assays to identify a pathogen-derived marker of early infection that is complementary to evaluation of the host immune response.

The investigators will conduct a prospective cohort study recruiting HWs at Tygerberg Hospital in Cape Town, where our prior study demonstrated the feasibility of recruiting this population. The investigators will recruit equal numbers of men and women and ensure participant diversity reflective of the South African population. The investigators will conduct serial testing every 3 months (based on a systematic review suggesting this testing interval may be optimal while being pragmatically feasible) with a combination of established and novel assays chosen to evaluate host and pathogen-derived signatures never evaluated before in parallel to identify correlates of risk and protection: IGRAs, novel LTBI tests, blood RNA biosignatures, Mtb-specific antibody responses and Mtb DNA detection assays. HWs are a unique population to understand serial host and pathogen dynamics including whether tests revert to negative i.e. whether initial IGRA conversions are transient versus persistent, and whether re-conversions may potentially represent reinfection given high exposure risk.

Inclusion Criteria:

• ≥18 years old
• Health worker
• Able to provide informed consent

Exclusion Criteria:

• Prior history of TB or known prior positive IGRA
• Current or prior history of taking anti-TB treatment

The study population will be health workers (primarily clinical but may include support staff) who are >18 years of age.