Face-mask sampling or sputum to diagnose lung tuberculosis?
Authors: Graham H Bothamley, Viktoria Spong
Journal: The Lancet Infectious Diseases (2020)

More than a third of people estimated to have tuberculosis in 2018 were undiagnosed or detected but not notified.1WHOGlobal tuberculosis report.https://apps.who.int/iris/bitstream/handle/10665/329368/9789241565714-eng.pdfDate: 2019Date accessed: January 16, 2020Google Scholar In India, a review of the Revised National Tuberculosis Control programme in 2013 estimated that 72% of individuals with tuberculosis reached a diagnostic centre, 60% were diagnosed, and 53% registered for treatment.2Subbaraman R Nathavitharana RR Satyanarayana S et al.The tuberculosis cascade of care in India's public sector: a systematic review and meta-analysis.PLoS One. 2017; 12e0183240PubMed Google Scholar To improve this situation, people who fear they might have tuberculosis should have access to cheap diagnostic tests, which can be posted or otherwise delivered to a laboratory and that provide sufficient information so the individual can receive the result and begin treatment if needed. In The Lancet Infectious Diseases, Caroline Williams and colleagues have assessed the effectiveness of face-mask sampling as a diagnostic method for tuberculosis.3Williams CM Abdulwhhab M Birring SS et al.Exhaled Mycobacterium tuberculosis output and detection of subclinical disease by face-mask sampling: prospective observational studies.Lancet Infect Dis. 2020; (published online Feb 18.)http://dx.doi.org/10.1016/S1473-3099(19)30707-8Summary Full Text Full Text PDF PubMed Scopus (46) Google Scholar Their approach could be a possible solution to a patient-led test. Most participants were happy to wear a face mask overnight; however, interruptions for face-mask changes in the protocol led to withdrawals from the study. Early disease that could only be detected by specialist radiology (PET-CT scans) was recognised by face-mask sampling in patients with symptoms suggesting tuberculosis, although most had HIV co-infection, a well known cause of a positive sputum smear or culture with an apparently normal chest radiograph.4Aderaye G Bruchfeld J Assefa G et al.The relationship between disease pattern and disease burden by chest radiography, M tuberculosis load, and HIV status in patients with pulmonary tuberculosis in Addis Ababa.Infection. 2004; 32: 333-338Crossref PubMed Scopus (44) Google Scholar What are the problems with sputum sampling? First, the diagnosis of tuberculosis needs to be considered by a health-care worker; access to health care and the cost of diagnostic tests for tuberculosis are limitations. Many people who think they might have been in contact with tuberculosis perceive a barrier in approaching health-care workers, either from cost, time constraints, concerns about loss of anonymity, or that attendance at a clinic will actually give them tuberculosis if they did not have it in the first place. Much emphasis has been placed on ensuring that sputum is not saliva and comes from deep within the chest.5Toman K What are the main causes of false-positive and false-negative sputum smears?.in: Frieden T Toman's tuberculosis: case detection, treatment, and monitoring—questions and answers. World Health Organization, Geneva2004: 23-27Google Scholar Sputum is difficult to obtain from those who are very unwell. Many patients require sputum induction to produce a sample for the laboratory. Negative pressure ventilation for infection control and the nebuliser and its supplies are expensive. The patient is left alone in the room and has to follow detailed instructions. Barriers in language and understanding mean that sputum may be swallowed or vomited and relatives might not want to leave the room. The process can take 40 min or more. The molecular assay Xpert MTB/RIF Ultra is widely available. However, the result can take more than 2 h to be ready, and the patient might not want to stay at the clinic for that period to receive the result. Sputum can be stored in tubes containing cetylpyridinium or alcohol for later testing with the Xpert assay.6N'Dira Sanoussi C de Jong BC Affolabi D Meehan CJ Odoun M Rigouts L Storage of sputum in cetylpyridinium chloride, OMNIgene.SPUTUM, and ethanol is compatible with molecular tuberculosis diagnostic testing.J Clin Microbiol. 2019; 57: e00275-e00319PubMed Google Scholar Containers can be made available at a pharmacist with a requirement to complete details for return of the result, but sputum samples might not be of good quality. If the Xpert test were positive, both a notification and information where to obtain treatment should follow automatically. Data from Williams and colleagues' study are preliminary.3Williams CM Abdulwhhab M Birring SS et al.Exhaled Mycobacterium tuberculosis output and detection of subclinical disease by face-mask sampling: prospective observational studies.Lancet Infect Dis. 2020; (published online Feb 18.)http://dx.doi.org/10.1016/S1473-3099(19)30707-8Summary Full Text Full Text PDF PubMed Scopus (46) Google Scholar They studied 24 patients with known positive cultures in a 24-h longitudinal study and 20 patients with symptoms of tuberculosis in an active case-finding pilot study. Of the 20 patients in the pilot study, eight were thought to have tuberculosis after testing, of whom six were exclusively positive from face-mask sampling. Four of these six participants had normal findings on chest radiography but lesions were present after more specialist radiology. Can the same sensitivity be achieved by face-mask sampling overnight or after 1 h? For an HIV-infected population, does the test serve better than a urine test for lipoarabinomannan?7Shah M Hanrahan C Wang ZY et al.Lateral flow urine lipoarabinomannan assay for detecting active tuberculosis in HIV-positive adults.Cochrane Database Syst Rev. 2016; 5CD011420Google Scholar, 8Gupta-Wright A Corbett EL van Oosterhout JJ et al.Rapid urine-based screening for tuberculosis in HIV-positive patients admitted to hospital in Africa (STAMP): a pragmatic, multicentre, parallel-group, double-blind, randomised controlled trial.Lancet. 2018; 392: 292-301Summary Full Text Full Text PDF PubMed Scopus (118) Google Scholar Does the test work well in a population without HIV co-infection? Could contacts be assessed by such a non-invasive technique?9Esmail H Lai RP Lesosky M et al.Characterization of progressive HIV-associated tuberculosis using 2-dexoy-2-[18F]fluoro-D-glucose positron emission and computed tomography.Nat Med. 2016; 22: 1090-1093Crossref PubMed Scopus (117) Google Scholar Cost will be an important factor in the future use of face-mask sampling. Polyvinyl alcohol, used in the face mask, is a plastic but can be degraded by Gram-negative bacteria (eg, pseudomonads), some Gram-positive bacteria, and lipolytic fungi,10Kawai F Hu X Biochemistry of microbial polyvinyl alcohol degradation.Appl Microbiol Biotech. 2009; 84: 227Crossref PubMed Scopus (135) Google Scholar assuaging potential environmental concerns over its use. New ideas to tackle early diagnosis of tuberculosis are needed, and face-mask sampling represents an interesting and innovative approach. We declare no competing interests. Exhaled Mycobacterium tuberculosis output and detection of subclinical disease by face-mask sampling: prospective observational studiesFace-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. Full-Text PDF Open Access