Previous tuberculosis modifies spirometry outcomes among small-scale gemstone miners in Tanzania: a cross-sectional, clinic-based study

TL;DR

Previous tuberculosis significantly worsens lung function in small-scale gemstone miners in Tanzania, even after accounting for silica exposure.

Contribution

This study quantifies the impact of previous TB on spirometry outcomes in miners using a clinic-based cohort and statistical modeling.

Findings

Miners with previous TB had 51% moderate FEV1 reductions compared to 18% without TB.

TB-positive miners with 10 years of work lost ~1400 mls of FEV1 compared to ~700 mls in TB-negative miners.

Abnormal spirometry remains significant even after accounting for potential silicosis.

Abstract

Small-scale miners are known to experience high silica exposures, associated with high rates of silicosis and Tuberculosis (TB). TB has been shown to worsen underlying impairment of lung function in miners. We describe the spirometry outcomes, according to previous TB status, among a large cohort of small-scale miners attending a screening centre.

We collected cross-sectional spirometry and clinical data from consecutive miners and ex-miners, with negative Xpert TB results, attending a screening clinic in Northern Tanzania, between February 2018 and December 2020. Spirometry values assessed using the ATS/ERS 2019 quality criteria and compared with GLI 2022 global (GLIgl) reference values. We used multiple linear regression to model excess Forced Expiratory Volume in 1 s (FEV1) and Forced Vital Capacity (FVC) loss using an a priori interaction between duration of work and previous TB.

Of 542 participants with spirometry results, 80 (15%) reported previous TB. At least moderate (z-score ≤−2.5) FEV1 reductions were present in 51% of participants with previous TB and 18% of those without previous TB. For FVC, respective values were 34% and 10%. A miner with TB and 10 years of work was modelled to have lost 1405 (95% CI 1134 to 1676) mls of FEV1 and 1342 (95% CI 1042 to 1641) mls of FVC compared with GLIgl reference values. For miners without previous TB, the corresponding excess FEV1 and FVC losses were 693 (95% CI 581 to 804) mls and 624 (95% CI 504 to 743) mls, respectively.

Unmeasured silicosis may partially explain some of the observed effect of previous TB. However, this does not change our observation of a clinically significant burden of abnormal spirometry in a clinic-based population of small-scale miners. Reducing silica exposures and preventing TB are key to improving lung health in miners.

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