Baseline predictors of sputum culture conversion in pulmonary tuberculosis : importance of cavities, smoking, time to detection and W-Beijing genotype
Date
2012-01-04
Journal Title
Journal ISSN
Volume Title
Publisher
PLOS
Abstract
Background: Time to detection (TTD) on automated liquid mycobacterial cultures is an emerging biomarker of tuberculosis
outcomes. The M. tuberculosis W-Beijing genotype is spreading globally, indicating a selective advantage. There is a paucity
of data on the association between baseline TTD and W-Beijing genotype and tuberculosis outcomes.
Aim: To assess baseline predictors of failure of sputum culture conversion, within the first 2 months of antitubercular
therapy, in participants with pulmonary tuberculosis.
Design: Between May 2005 and August 2008 we conducted a prospective cohort study of time to sputum culture
conversion in ambulatory participants with first episodes of smear and culture positive pulmonary tuberculosis attending
two primary care clinics in Cape Town, South Africa. Rifampicin resistance (diagnosed on phenotypic susceptibility testing)
was an exclusion criterion. Sputum was collected weekly for 8 weeks for mycobacterial culture on liquid media (BACTEC
MGIT 960). Due to missing data, multiple imputation was performed. Time to sputum culture conversion was analysed using
a Cox-proportional hazards model. Bayesian model averaging determined the posterior effect probability for each variable.
Results: 113 participants were enrolled (30.1% female, 10.5% HIV-infected, 44.2% W-Beijing genotype, and 89% cavities). On
Kaplan Meier analysis 50.4% of participants underwent sputum culture conversion by 8 weeks. The following baseline
factors were associated with slower sputum culture conversion: TTD (adjusted hazard ratio (aHR) = 1.11, 95% CI 1.02; 1.2),
lung cavities (aHR = 0.13, 95% CI 0.02; 0.95), ever smoking (aHR = 0.32, 95% CI 0.1; 1.02) and the W-Beijing genotype
(aHR = 0.51, 95% CI 0.25; 1.07). On Bayesian model averaging, posterior probability effects were strong for TTD, lung
cavitation and smoking and moderate for W-Beijing genotype.
Conclusion: We found that baseline TTD, smoking, cavities and W-Beijing genotype were associated with delayed 2 month
sputum culture. Larger studies are needed to confirm the relationship between the W-Beijing genotype and sputum culture
conversion.
Description
Keywords
Mycobacterial cultures, Time to detection (TTD), M. tuberculosis W-Beijing genotype, Sputum culture conversion, Genotype-environment interaction, Mycobacterium tuberculosis -- Diagnosis, W-Beijing genotype
Citation
Visser M. E., Stead M. C., Walzl G. Warren R. Schomaker M. et al. (2012) Baseline Predictors of Sputum Culture Conversion in Pulmonary Tuberculosis: Importance of Cavities, Smoking, Time to Detection and W-Beijing Genotype. PLoS ONE 7(1): e29588.