Comparative value of sputum smear examination and culture examination in assessing the progress of tuberculous patients receiving chemotherapy

Bacteriological response is generally considered the best criterion for assessing the efficacy of chemotherapy in patients with pulmonary tuberculosis. The bacteriological methods most commonly used are examination of sputum smears for tubercle bacilli, culture of bacilli from sputum specimens, and drug-sensitivity tests on positive cultures. Culture examination, though more sensitive than smear examination in detecting tubercle bacilli, is time-consuming and economically impracticable as a routine method in most developing countries. A study was therefore undertaken at the Tuberculosis Chemotherapy Centre, Madras, to determine the relative value of smear examination and culture examination in predicting the outcome of treatment and assessing the efficacy of chemotherapeutic regimens in 515 patients (all with bacteriologically confirmed disease and isoniazid-sensitive organisms on admission) receiving isoniazid, alone or with sodium PAS. The results showed that the value of smear examination of overnight sputum specimens at monthly intervals closely approached that of culture examination in assessing the progress of the patients, the percentages of correct predictions by smear and by culture being of the same order. Smear examination was slightly less effective than culture examination in detecting differences in the efficacies of regimens, but it has been estimated that this disadvantage can usually be compensated for by increasing the study population by about 20%.