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Rationale: The diagnosis of latent tuberculosis (TB) infection (LTBI) is complicated by the absence of a gold standard. Discordance between tuberculin skin tests (TST) and interferon gamma release assays (IGRA) occurs in 10-20% of individuals, but the underlying mechanisms are poorly understood., Methods: We analyzed data from a prospective household contact study that included cough aerosol culture results from index cases, environmental and contact factors. We assessed contacts for LTBI using TST and IGRA at baseline and six weeks. We examined TST/IGRA discordance in qualitative and quantitative analyses, and used multivariable logistic regression analysis with generalized estimating equations to analyze predictors of discordance., Measurements and Results: We included 96 TB patients and 384 contacts. Discordance decreased from 15% at baseline to 8% by six weeks. In adjusted analyses, discordance was related to less crowding (p = 0.004), non-cavitary disease (OR 1.41, 95% CI: 1.02-1.96; p = 0.03), and marginally with BCG vaccination in contacts (OR 1.40, 95% CI: 0.99-1.98, p = 0.06)., Conclusions: We observed significant individual variability and temporal dynamism in TST and IGRA results in household contacts of pulmonary TB cases. Discordance was associated with a less intense infectious exposure, and marginally associated with a BCG-mediated delay in IGRA conversion. Cough aerosols provide an additional dimension to the assessment of infectiousness and risk of infection in contacts.

Rationale: The degree to which tuberculosis (TB) is transmitted between persons is variable. Identifying the factors that contribute to transmission could provide new opportunities for TB control. Transmission is influenced by host, bacterial and environmental factors. However, distinguishing their individual effects is problematic because measures of disease severity are tightly correlated, and assessing the virulence of Mycobacterium tuberculosis isolates is complicated by epidemiological and clinical confounders., Objectives: To overcome these problems, we investigated factors potentially associated with TB transmission within households., Methods: We evaluated patients with smear-positive (≥2+), pulmonary TB and classified M. tuberculosis strains into single nucleotide polymorphism genetic cluster groups (SCG). We recorded index case, household contact, and environmental characteristics and tested contacts with tuberculin skin test (TST) and interferon-gamma release assay. Households were classified as high (≥70% of contacts with TST≥10 mm) and low (≤40%) transmission. We used logistic regression to determine independent predictors., Result: From March 2008 to June 2012, we screened 293 TB patients to enroll 124 index cases and their 731 contacts. There were 23 low and 73 high transmission households. Index case factors associated with high transmission were severity of cough as measured by a visual analog cough scale (VACS) and the Leicester Cough Questionnaire (LCQ), and cavitation on chest radiograph. SCG 3b strains tended to be more prevalent in low (27.3%) than in high (12.5%) transmission households (p = 0.11). In adjusted models, only VACS (p<0.001) remained significant. SCG was associated with bilateral disease on chest radiograph (p = 0.002) and marginally associated with LCQ sores (p = 0.058), with group 3b patients having weaker cough., Conclusions: We found differential transmission among otherwise clinically similar patients with advanced TB disease. We propose that distinct strains may cause differing patterns of cough strength and cavitation in the host leading to diverging infectiousness. Larger studies are needed to verify this hypothesis.

Rationale: Airborne transmission of Mycobacterium tuberculosis results from incompletely characterized host, bacterial, and environmental factors. Sputum smear microscopy is associated with considerable variability in transmission., Objectives: To evaluate the use of cough-generated aerosols of M. tuberculosis to predict recent transmission., Methods: Patients with pulmonary tuberculosis (TB) underwent a standard evaluation and collection of cough aerosol cultures of M. tuberculosis. We assessed household contacts for new M. tuberculosis infection. We used multivariable logistic regression analysis with cluster adjustment to analyze predictors of new infection., Measurements and Main Results: From May 2009 to January 2011, we enrolled 96 sputum culture-positive index TB cases and their 442 contacts. Only 43 (45%) patients with TB yielded M. tuberculosis in aerosols. Contacts of patients with TB who produced high aerosols (≥10 CFU) were more likely to have a new infection compared with contacts from low-aerosol (1-9 CFU) and aerosol-negative cases (69%, 25%, and 30%, respectively; P = 0.009). A high-aerosol patient with TB was the only predictor of new M. tuberculosis infection in unadjusted (odds ratio, 5.18; 95% confidence interval, 1.52-17.61) and adjusted analyses (odds ratio, 4.81; 95% confidence interval, 1.20-19.23). Contacts of patients with TB with no aerosols versus low and high aerosols had differential tuberculin skin test and interferon-γ release assay responses., Conclusions: Cough aerosols of M. tuberculosis are produced by a minority of patients with TB but predict transmission better than sputum smear microscopy or culture. Cough aerosols may help identify the most infectious patients with TB and thus improve the cost-effectiveness of TB control programs.