Quantification of M. tuberculosis DNA in Sputum During the Treatment of Pulmonary Tuberculosis.
The most common laboratory measures of response to therapy for patients with pulmonary tuberculosis are conversion of acid-fast bacilli (AFB) sputum smear to negative, or culture positive sputum to negative. AFB enumeration lacks sensitivity and specificity and the culture of M. tuberculosis (MTB) bacteria can take weeks. Quantitative estimates of MTB DNA in sputum have been shown to correlate with numbers of viable bacilli before the onset of chemotherapy (1-3). Once effective treatment has been initiated, DNA levels remain high in comparison to viable MTB counts in a majority of smear-positive patients and thus do not serve as a marker for the bactericidal response observed in sputa.