Comparison of Sputum-Culture Conversion for Mycobacterium bovis and M. tuberculosis

Abstract

Current US guidelines recommend longer treatment for tuberculosis (TB) caused by pyrazinamide-resistant organisms (e.g., Mycobacterium bovis) than for M. tuberculosis TB. We compared treatment response times for patients with M. bovis TB and M. tuberculosis TB reported in the United States during 2006-2013. We included culture-positive, pulmonary TB patients with genotyping results who received standard 4-drug treatment at the time of diagnosis. Time to sputum-culture conversion was defined as time between treatment start date and date of first consistently culture-negative sputum. We analyzed 297 case-patients with M. bovis TB and 30,848 case-patients with M. tuberculosis TB. After 2 months of treatment, 71% of M. bovis and 65% of M. tuberculosis TB patients showed conversion of sputum cultures to negative. Likelihood of culture conversion was higher for M. bovis than for M. tuberculosis, even after controlling for treatment administration type, sex, and a composite indicator of bacillary burden.

Keywords: Mycobacterium bovis; Mycobacterium tuberculosis; bacteria; disease; sputum; sputum-culture conversion; tuberculosis; tuberculosis and other mycobacteria.

Figure 1

Selection of tuberculosis cases for analysis of sputum-culture conversion, United States, 2006–2013. Analysis included cases of culture-positive disease. A total of 61% of case-patients with M. bovis TB and 63% of case-patients with M. tuberculosis TB met analytic requirements for inclusion. PZA, pyrazinamide; TB, tuberculosis. Mycobacterium tuberculosis with pyrazinamide resistance (n = 757).

Figure 2

Time to sputum-culture conversion for case-patients with Mycobacterium bovis and M. tuberculosis TB, United States, 2006–2013. At day 0, a total of 297 persons had culture-positive M. bovis TB and 30,848 had culture-positive M. tuberculosis TB; at day 20, a total of 239 persons had culture-positive M. bovis TB and 25,363 had culture-positive M. tuberculosis TB; at day 40, a total of 143 persons had culture-positive M. bovis TB and 17,882 had culture-positive M. tuberculosis TB; at day 60, a total of 85 persons had culture-positive M. bovis TB and 10,853 had culture-positive M. tuberculosis TB; and at day 80, a total of 47 persons had culture-positive M. bovis TB and 6,084 had culture-positive M. tuberculosis TB. TB, tuberculosis.