Detection of aerosolized Mycobacterium tuberculosis DNA from adults being investigated for pulmonary tuberculosis using an electrostatic sampler in a South African primary care setting

Background Non-sputum-based diagnosis of tuberculosis is a public health priority. Little is known about the feasibility of detecting Mycobacterium tuberculosis complex (Mtb) DNA in respiratory aerosols in primary care, its diagnostic value, and clinical and microbiological characteristics associated with detection. Methods We recruited symptomatic adults self-presenting to South African primary care clinics with a sputum Xpert MTB/RIF Ultra (Ultra) result. Cough aerosols were collected on-site using TB Hotspot detectOR (THOR), a novel electrostatic aerosol sampler, and tested by Ultra. Environmental and laboratory controls were collected. Predictors of aerosol Mtb DNA (AMD) detection were assessed. Results Amongst 137 participants, 71 (52%) had medium or high and 34 (25%), had negative sputum Ultra semi-quantitative results. Compared to sputum Ultra detection, AMD detection sensitivity and specificity was 46.6% (95%CI: 42.5, 50.7) and 76.5% (95%CI: 70.4, 82.5) respectively. Sensitivity was higher in people with a sputum-Ultra semi-quantitation category of high (56.9%; 95%CI: 51.1, 62.7). Factors associated with AMD detection were male sex with sputum Ultra semi-quantitative result medium or greater (aRR 3.26; 95%CI: 1.11, 9.55; p=0.024) and reported fever (aRR 0.58; 95%CI: 0.29, 1.07; p=0.099). Sputum-to-aerosol ratios were ≥ 0.75 in three participants, suggesting a high capacity to expel Mtb DNA. Despite rigorous decontamination, AMD was detected from 30% of environmental samples highlighting THOR’s potent sampling capability and potential nosocomial transmission risks. Conclusions Electrostatic aerosol sampling is feasible in primary care to detect people with infectious tuberculosis. Deployment of this and other practical aerosol sampling tools might help to characterize predictors of tuberculosis transmission.