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Abstract
Introduction All pulmonary tuberculosis (PTB) cases are presumed to be infectious to some degree. This spectrum of infectiousness is independently described by both the acid-fast bacilli smear and radiographic findings. Smear-positive patients with chest radiographic findings that are typical for adult-type PTB are believed to be most infectious.
Hypothesis Characterisation of the presumed most infectious PTB case is possible by reference to readily available clinical features and laboratory results.
Methods Retrospective cohort study of adult, culture-positive PTB cases (151 smear-positive; 162 smear-negative) diagnosed between 1 January 2013 and 30 April 2017 in Canada. We describe cases according to demographic, clinical and laboratory features. We use multivariable multinomial logistic regression to estimate the relative risk ratio (RRR) with 95% CI of features associated with an outcome of smear-positive PTB, characterised by ‘typical’ chest radiograph findings.
Results Being Canadian-born, symptomatic, having a subacute duration of symptoms and broad-spectrum antibiotic prescriptions were all more commonly associated with smear-positive than smear-negative disease (36% vs 20%; 95% vs 63%; 88% vs 54%; and 59% vs 28%, respectively). After combining smear status and radiographic features, we show that smear-positive patients with typical chest radiographs were younger, had a longer duration of symptoms (RRR 2.41; 95% CI 1.01 to 5.74 and 2.93; 95% CI 1.20 to 7.11, respectively) and were less likely to be foreign-born, or have a moderate to high-risk factor for reactivation (RRR 0.40; 95% CI 0.17 to 0.92 and 0.18; 95% CI 0.04 to 0.71, respectively) compared with smear-negative patients with atypical chest radiograph findings.
Conclusion A clear picture of the presumed most infectious PTB case emerges from available historical and laboratory information; vigilance for this presentation by front-line providers will support elimination strategies aimed at reducing transmission.
- tuberculosis
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Footnotes
Contributors CH and RL conceived this study. CH analysed and interpreted the data and provided initial drafts. JB interpreted the radiographs and was involved in critical review. AD and AS provided assistance with statistical methods and critical reviews. MLE and CP abstracted and collated relevant clinical data and provided critical reviews. RL interpreted the chest radiographs and provided expert oversight and critical reviews for all the drafts.
Funding An Alberta Lung Association/Respiratory Health Strategic Clinical Health Network Studentship, and the University of Alberta Pulmonary Research Group award provided financial support to the lead author for her studies, of which this work represents one part.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. All data are available upon reasonable request made to the corresponding author. Subsequent secondary analyses will be subject to appropriate REB approvals as necessary.