Abstract
Background:Tuberculosis (TB) is predominantly an airborne disease. However, quantitative and qualitative analysis of bio-aerosols containing the aetiological agent, Mycobacterium tuberculosis (Mtb), has proven very challenging. Our objective is to sample bio-aerosols from newly diagnosed TB patients for detection and enumeration of Mtb bacilli. Methods:We monitored each of 35 newly diagnosed, GeneXpert sputum-positive, TB patients during 1 hour confinement in a custom-built Respiratory Aerosol Sampling Chamber (RASC). The RASC (a small clean-room of 1.4m ) incorporates aerodynamic particle size detection, viable and non-viable sampling devices, real-time CO 2 monitoring, and cough sound-recording. Microbiological culture and droplet digital polymerase chain reaction (ddPCR) were used to detect Mtb in each of the bio-aerosol collection devices. Results: Mtb was detected in 27/35 (77.1%) of aerosol samples; 15/35 (42.8%) samples were positive by mycobacterial culture and 25/27 (92.96%) were positive by ddPCR. Culturability of collected bacilli was not predicted by radiographic evidence of pulmonary cavitation, sputum smear positivity. A correlation was found between cough rate and culturable bioaerosol. Mtb was detected on all viable cascade impactor stages with a peak at aerosol sizes 2.0-3.5μm. This suggests a median of 0.09 CFU/litre of exhaled air (IQR: 0.07 to 0.3 CFU/l) for the aerosol culture positives and an estimated median concentration of 4.5x10 CFU/ml (IQR: 2.9x10 -5.6x10 ) of exhaled particulate bio-aerosol. Conclusions: Mtb was identified in bio-aerosols exhaled by the majority of untreated TB patients using the RASC. Molecular detection was more sensitive than mycobacterial culture on solid media, suggesting that further studies are required to determine whether this reflects a significant proportion of differentially detectablebacilli in these samples.
Highlights
Tuberculosis (TB) has surpassed HIV/AIDS as a global killer with more than 4000 daily deaths[1]
Baseline characteristics and microbiological results A total of 35 participants were recruited for this study (Table 1), all of whom had drug-sensitive pulmonary TB defined by a positive GeneXpert sputum
15 participants (42.9%) had a positive bio-aerosol mycobacterial culture, which was defined as one or more colony forming units (CFU) detected on any of the sampling devices (Figure 1A). 59 CFU exhibited the morphologies and growth rates characteristic of Mycobacterium tuberculosis (Mtb) grown in vitro on solid media, and this was confirmed by RD9 genotype in 37 cases
Summary
Tuberculosis (TB) has surpassed HIV/AIDS as a global killer with more than 4000 daily deaths[1]. Venting exhaled air from pulmonary TB patients over a guinea pig facility resulted in infection of the animals leading to the concept of infectious ‘quanta’ (the dose of infectious air required to cause an infection). These pioneering studies indicated that quanta production was extremely infrequent and definitively attributable to only a small minority of patients. Mtb was detected on all viable cascade impactor stages with a peak at aerosol sizes 2.0-3.5μm This suggests a median of 0.09 CFU/litre of exhaled air (IQR: 0.07 to 0.3 CFU/l) for the aerosol culture positives and an estimated median concentration of 4.5x10 7 CFU/ml (IQR: 2.9x10 7-5.6x10 7) of exhaled particulate bio-aerosol. Molecular detection was more sensitive than mycobacterial culture on solid media, suggesting that further studies are required to determine whether this reflects a significant proportion of
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