Background: Cough is the major determinant of tuberculosis transmission. Despite this, there is a paucity of information regarding characteristics of cough frequency throughout the day and in response to tuberculosis therapy. Here we evaluate the circadian cycle of cough; cough frequency risk factors; and the impact of appropriate treatment on cough and bacillary load. Methods: We prospectively evaluated HIV-negative adults (n=64) with a new diagnosis of culture-proven, drug-susceptible pulmonary tuberculosis immediately prior to treatment and repeatedly until treatment day 62. At each time-point, participant cough was recorded (n=670) and analyzed using the Cayetano Cough Monitor. Consecutive coughs at least 2-seconds apart were counted as separate cough episodes. Sputum samples (n=426) were tested with microscopic-observation drug-susceptibility broth culture, and in culture-positive samples (n=252) the time to culture positivity was used to estimate bacillary load. Results: The highest cough frequency occurred from 1-2 p.m., and the lowest from 1-2 a.m. (2.4 versus 1.1 cough episodes/hour, respectively). Cough frequency was higher among participants who had higher sputum bacillary load (p<0.01). Pre-treatment median cough episodes/hour was 2.3 (IQR=1.2-4.1), which at 14 treatment days decreased to 0.48 (IQR=0.0-1.4) and at the end of the study decreased to 0.18 (IQR=0.0-0.59), both reductions p<0.001. By 14 treatment days, the probability of culture conversion was 29% (95% CI=19-41%). Conclusions: Coughs were most frequent during daytime. Two weeks of appropriate treatment significantly reduced cough frequency and made one-third of participants achieve culture conversion. Thus treatment by two weeks considerably diminishes but not eliminates the potential for airborne tuberculosis transmission.
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