Neil M. Ampel, MD reviewing Jones-López EC et al. Clin Infect Dis 2016 Jul 1.

In a Ugandan study, contacts exposed to patients with ≥10 CFU of M. tuberculosis in a cough aerosol culture had excess risk for active tuberculosis.

Among individuals exposed to pulmonary tuberculosis (TB), rates of infection and disease vary substantially. The number of colony forming units (CFUs) in cough aerosols from persons with pulmonary TB has been shown to predict new infection among close contacts better than sputum acid-fast bacillus (AFB) smears. Are household contacts of TB patients with high aerosol production at greater risk for progressing than contacts of patients with low or negative aerosol production? To answer this question, investigators enrolled 85 consecutive adult patients in Uganda with pulmonary TB and their 369 household contacts. Patients coughed into an aerosol sampling system for culture of Mycobacterium tuberculosis. Results were considered negative, low aerosol (1–9 CFUs), or high aerosol (≥10 CFUs). Participants were followed for a median of 3.9 years.

Occurrence of TB skin test indurations ≥10 mm was more likely among contacts of high-aerosol cases than among contacts of negative or low-aerosol cases (94% vs. 80%; P=0.002). In adjusted analysis, the odds ratio of a contact developing active TB following exposure to a high-aerosol case was 6.0 (P=0.01); however, this odds ratio in a contact was 8.2 if the time-to-growth from the case's sputum culture was <6 days (P=0.04).

CITATION(S):

Jones-López EC et al. Cough aerosols of Mycobacterium tuberculosis in the prediction of incident tuberculosis disease in household contacts. Clin Infect Dis 2016 Jul 1; 63:10. 

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