BACKGROUND: The size and concentration of exhaled bioaerosols may influence TB transmission risk. This study piloted bioaerosol measurement in patients with TB and assessed variability in bioaerosol production during normal tidal breathing. Understanding this may provide a tool for assessing heterogeneity in infectivity and may inform mathematical models of TB control practices and policies. METHODS: Optical particle counter technology was used to measure aerosol size and concentration in exhaled air (range 0.3-20 µm in diameter) during 15 tidal breaths across four groups over time: healthy/uninfected, healthy/Mycobacterium tuberculosis-infected, patients with extrathoracic TB and patients with intrathoracic TB. High-particle production was defined as any 1-5 µm sized bioaerosol count above the median count among all participants (median count=2 counts/L). RESULTS: Data from 188 participants were obtained pretreatment (baseline). Bioaerosol production varied considerably between individuals. Multivariable analysis showed intrathoracic TB was associated with a 3½-fold increase in odds of high production of 1-5 µm bioaerosols (adjusted OR: 3.5; 95% CI 1.6 to 7.8; p=0.002) compared with healthy/uninfected individuals. CONCLUSIONS: We provide the first evidence that intrathoracic TB increases bioaerosol production in a particle size range that could plausibly transport M. tuberculosis. There is substantial variation in production within patients with TB that may conceivably relate to the degree of infectivity. Further data is needed to determine if high bioaerosol production during tidal breathing is associated with infectiousness.