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Home / The International Journal of Tuberculosis and Lung Disease, Volume 16, Number 11

Grading of a positive sputum smear and the risk of Mycobacterium tuberculosis transmission

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SETTING: After the diagnosis of a case of tuberculosis (TB), contact tracing is directed by the risk of transmission, for which sputum acid-fast bacilli (AFB) staining results are highly relevant. Limited data are available on the effect of the degree of acid-fast positivity, of a polymerase chain reaction (PCR) result or of bronchoalveolar lavage (BAL) fluid results on the risk of transmission.

OBJECTIVES: To investigate factors associated with TB transmission, focusing on quantitative sputum smear results.

DESIGN: Retrospective study of contact investigations performed over a period of 5 years in a Dutch Municipal Health Service among all index patients with TB, and the tuberculin skin test and chest radiography results in contacts. Three definitions of transmission were used: ≥1 or ≥5 contacts with positive TST or active TB in contacts.

RESULTS: The highest (+4/+5) sputum AFB grades were associated with the highest relative risk (≥8) of extensive transmission or active TB among contacts. Novel risk factors observed were employment or school attendance, positive PCR of sputum and positive AFB staining of BAL fluid. Pulmonary symptoms, infiltrate or cavity and positive AFB sputum stain were also associated with transmission, confirming previous studies.

CONCLUSION: The risk factors observed in this study may aid in the extension of contact investigations.

Keywords: PCR; acid-fast staining; bronchoalveolar lavage; contact investigation; tuberculin skin test

Document Type: Research Article

Affiliations: 1: Department of Infectious Diseases, Leiden University Medical Centre, Leiden, The Netherlands 2: Municipal Health Service (GG&GD), Division of Tuberculosis Control, Utrecht, The Netherlands 3: Department of Clinical Epidemiology, Leiden University Medical Centre, Leiden, The Netherlands 4: National Mycobacteria Reference Laboratory, National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands 5: National Mycobacteria Reference Laboratory, National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands; Department of Clinical Microbiology and Department of Pulmonary Diseases, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

Publication date: 01 November 2012

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  • The International Journal of Tuberculosis and Lung Disease (IJTLD) is for clinical research and epidemiological studies on lung health, including articles on TB, TB-HIV and respiratory diseases such as COVID-19, asthma, COPD, child lung health and the hazards of tobacco and air pollution. Individuals and institutes can subscribe to the IJTLD online or in print – simply email us at [email protected] for details.

    The IJTLD is dedicated to understanding lung disease and to the dissemination of knowledge leading to better lung health. To allow us to share scientific research as rapidly as possible, the IJTLD is fast-tracking the publication of certain articles as preprints prior to their publication. Read fast-track articles.

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