Quantification of airborne Mycobacterium tuberculosis in health care setting using real-time qPCR coupled to an air-sampling filter method

Mycobacterium tuberculosis infection remains one of the major public health issues worldwide. Current qualitative assays ( only positive or negative results) do not provide comprehensive information regarding health risk of M. tuberculosis. This study attempted to develop a quantitative assay to measure air concentration of M. tuberculosis in a health care setting. A total of 22 air samples were taken from the negative pressure isolation rooms of tuberculosis patients. The air was filtered through a Nuclepore filter with sampling time of 8 h. The DNA of M. tuberculosis in these airborne samples was then analyzed by the ABI 7700 real-time quantitative polymerase chain reaction (real-time qPCR) system. The real-time qPCR method could perform measurements of counts in a dynamic range of over 6 orders with a high sensitivity. The measured M. tuberculosis concentrations varied widely, from 1.43 x 10 copies/m(3) to 2.06 x 10(5) copies/m(3). Comparisons among airborne M. tuberculosis levels, sputum smear, results, and sputum culture results showed moderate correlations. The filter/real-time qPCR method proved extremely sensitive and rapid for quantifying airborne M. tuberculosis. In addition, it is a powerful sampling tool that has potential applications as an investigational device, which might be valuable in conducting studies that validate the efficacy of engineering controls and work practices.