Mycobacterium tuberculosis cough aerosol culture status associates with host characteristics and inflammatory profiles

Abstract

Interrupting transmission events is critical to tuberculosis control. Cough-generated aerosol cultures predict tuberculosis transmission better than microbiological or clinical markers. We hypothesize that highly infectious individuals with pulmonary tuberculosis (positive for cough aerosol cultures) have elevated inflammatory markers and unique transcriptional profiles compared to less infectious individuals. We performed a prospective, longitudinal study using cough aerosol sampling system. We enrolled 142 participants with treatment-naïve pulmonary tuberculosis in Kenya and assessed the association of clinical, microbiologic, and immunologic characteristics with Mycobacterium tuberculosis aerosolization and transmission in 129 household members. Contacts of the forty-three aerosol culture-positive participants (30%) are more likely to have a positive interferon-gamma release assay (85% vs 53%, P = 0.006) and higher median IFNγ level (P < 0.001, 4.28 IU/ml (1.77-5.91) vs. 0.71 (0.01-3.56)) compared to aerosol culture-negative individuals. We find that higher bacillary burden, younger age, larger mean upper arm circumference, and host inflammatory profiles, including elevated serum C-reactive protein and lower plasma TNF levels, associate with positive cough aerosol cultures. Notably, we find pre-treatment whole blood transcriptional profiles associate with aerosol culture status, independent of bacillary load. These findings suggest that tuberculosis infectiousness is associated with epidemiologic characteristics and inflammatory signatures and that these features may identify highly infectious persons.

Fig. 1. Association of blood and sputum inflammatory and microbiologic markers with cough aerosol culture positivity.

Inflammatory and microbiologic markers were measured in blood and sputum at baseline visits and correlated with cough aerosol culture positivity. a Serum CRP, Blood WBC, sputum bacillary load determined by GeneXpert Ct value, and sputum culture time to detection (n = 99 CAC-; n = 43 CAC + ). b–d Sputum and plasma cytokines measured by ELISA; CXCL8, IL1B, IL6, and TNF measurements at diagnosis were correlated with cough aerosol culture positivity (b), bacillary (c), and chest x-ray lung cavitation load (panels b-d: sputum CXCL8: n = 81 CAC-, n = 37 CAC +; sputum IL1B: n = 80 CAC-, n = 37 CAC +; sputum IL6: n = 82 CAC-, n = 38 CAC +; plasma IL6 & TNF: n = 91 CAC-, n = 41 CAC +) (d). For c, d cough aerosol culture-positive and cough aerosol culture-negative individuals are depicted with red or black circles, respectively. Figures (a), (b), and (d) are Tukey-style box plot statistics with the median line, hinges indicating the 1st and 3rd quartiles, and whiskers extending to maximum and minimum values within 1.5x the interquartile range of the upper and lower hinges. The graphs in (c) display the linear model fit to the data with shaded error regions indicating the 95% confidence interval of the fit. Analyses shown in 1(a) panels reflect bivariate logistic regression described in Table 1, those shown in 1(b) and 1(d) panels used two-sided Wilcoxon rank sum test with continuity correction, and 1(c) panels reflect linear models fit to log10 transformed cytokine concentration. ELISA was performed with technical duplicates on the same sample with highly discordant samples removed from further analysis; results were averaged for each participant. Gray circle, unknown cough aerosol culture status. Source data are provided as a Source Data file. *p < 0.05, **p < 0.01, ***p < 0.001.

Fig. 2. Whole blood transcriptional signatures and association with cough aerosol culture positivity and bacillary burden.

a Differential gene expression associated with cough aerosol culture positivity and bacillary load. The volcano plot shows the gene-wise covariate-adjusted log2 fold change associated with each effect as well as each gene’s Benjamini-Hochberg adjusted false discovery rate (FDR). b Distributions of unadjusted p-values (x-axis) and FDR (y-axis) for each effect. c Gene set enrichment of Hallmark pathways in differential gene expression of cough aerosol culture positivity (red) and bacillary load (yellow). Displayed at left are all pathways for which any effect showed enrichment at an FDR threshold of 0.2. For each effect, pathways with an enrichment FDR < 0.2 are indicated with solid points while open points reflect FDR > = 0.2; diamond-shaped points locate two pathways uniquely enriched in the expression signal associated with cough aerosol culture positivity. Pathways are organized by their maximum enrichment score for any of the two effects. The Venn diagram at right displays the number of pathways enriched in each effect at FDR < 0.2 with stratification by concordance of directionality of effect. d Leading edge genes driving enrichment of Hallmark pathways uniquely associated with cough aerosol culture-positive status. Points indicate the adjusted fold change associated with cough aerosol culture positivity (y position is arbitrary jitter), are colored according to the sign of FC, and filled/labeled points indicate leading edge genes in the GSEA analysis. Gray violins indicate the distribution of FC values within each pathway, and a rug plot along the x-axis indicates the full distribution of FCs estimates for the cough aerosol culture-positive effect. Black curves indicate the running enrichment score deviation from zero along the y-axis. Source data are provided as a Source Data file.