Exhaled Mycobacterium tuberculosis output and detection of subclinical disease by face-mask sampling: prospective observational studies

Abstract

Background: Tuberculosis remains a global health challenge, with early diagnosis key to its reduction. Face-mask sampling detects exhaled Mycobacterium tuberculosis. We aimed to investigate bacillary output from patients with pulmonary tuberculosis and to assess the potential of face-mask sampling as a diagnostic method in active case-finding.

Methods: We did a 24-h longitudinal study in patients from three hospitals in Pretoria, South Africa, with microbiologically confirmed pulmonary tuberculosis. Patients underwent 1 h of face-mask sampling eight times over a 24-h period, with contemporaneous sputum sampling. M tuberculosis was detected by quantitative PCR. We also did an active case-finding pilot study in inhabitants of an informal settlement near Pretoria. We enrolled individuals with symptoms of tuberculosis on the WHO screening questionnaire. Participants provided sputum and face-mask samples that were tested with the molecular assay Xpert MTB/RIF Ultra. Sputum-negative and face-mask-positive individuals were followed up prospectively for 20 weeks by bronchoscopy, PET-CT, and further sputum analysis to validate the diagnosis.

Findings: Between Sept 22, 2015, and Dec 3, 2015, 78 patients with pulmonary tuberculosis were screened for the longitudinal study, of whom 24 completed the study (20 had HIV co-infection). M tuberculosis was detected in 166 (86%) of 192 face-mask samples and 38 (21%) of 184 assessable sputum samples obtained over a 24-h period. Exhaled M tuberculosis output showed no diurnal pattern and did not associate with cough frequency, sputum bacillary content, or chest radiographic disease severity. On May 16, 2018, 45 individuals were screened for the prospective active case-finding pilot study, of whom 20 had tuberculosis symptoms and were willing to take part. Eight participants were diagnosed prospectively with pulmonary tuberculosis, of whom six were exclusively face-mask positive at screening. Four of these participants (three of whom were HIV-positive) had normal findings on chest radiography but had treatment-responsive early tuberculosis-compatible lesions on PET-CT scans, with Xpert-positive sputum samples after 6 weeks.

Interpretation: Face-mask sampling offers a highly efficient and non-invasive method for detecting exhaled M tuberculosis, informing the presence of active infection both with greater consistency and at an earlier disease stage than with sputum samples. The approach shows potential for diagnosis and screening, particularly in difficult-to-reach communities.

Funding: Wellcome Trust, CARA (Council for At-Risk Academics), University of Leicester, the UK Medical Research Council, and the National Institute for Health Research. VIDEO ABSTRACT.

Figure 1

Longitudinal study profile Patients all had pulmonary tuberculosis confirmed by sputum acid-fast bacilli smear or molecular assay with Xpert MTB/RIF.

Figure 2

Mycobacterial output in face-mask and sputum samples, with cough counts over 24 h Cumulative Mycobacterium tuberculosis output in 21 patients (A); three of 24 patients who completed the study were excluded from this analysis because of an error in the processing of their sputum samples. Pattern of M tuberculosis output and cough count over 24 h (B).

Figure 3

Active case-finding pilot study profile Patients were all living in an informal settlement and were screened with the WHO tuberculosis symptom screening questionnaire. Xpert=molecular assay Xpert MTB/RIF Ultra. *Follow-up at 6 weeks consisted of repeat Xpert analysis of face-mask and sputum samples, bronchoalveolar lavage with Xpert analysis, chest radiography, and PET-CT. Follow-up at 20 weeks consisted of repeat Xpert analysis of face-mask and sputum samples, propidium monoazide and Xpert analysis of face-mask samples, and repeat PET-CT.

Figure 4

PET-CT images from four patients investigated for tuberculosis Four patients who were face-mask-positive but sputum-negative for Mycobacterium tuberculosis at screening were followed up for 20 weeks. Matched 6-week (left) and 20-week (right) images for each patient (A–D). CT images are shown in the upper windows, PET scans in the middle windows, and the fused dataset in the lower windows. (A–C) Arrows show parenchymal lung changes (tree and bud) with associated increased F-fluorodeoxyglucose uptake on the 6-week scan, which resolved completely at 20 weeks. (D) Arrows show mediastinal and left hilar lymph nodes, which were active on the 6-week scan and resolved completely at 20 weeks.