Time to Sputum Culture Conversion and the Intensive Phase Treatment Outcomes in South African Patients with Rifampicin Mono-Resistant Tuberculosis

Background: Sputum culture conversion from positive to negative is an important indicator of the efficacy of tuberculosis treatment and has been used to predict outcomes of tuberculosis therapy. Therefore, the aim of this study was to determine the time to sputum culture conversion and the outcomes of intensive phase treatment among patients with Rifampicin mono-resistant tuberculosis (RMR-TB) in South Africa.

Methods: This was a retrospective cohort study involving 335 RMR-TB patients who were treated between January 2009 and 31 December 2015 at Brewelskoof Hospital in the Western Cape Province, South Africa. The cohort consisted of male and female patients aged 18 to 65 years old. The patient’s demographic and clinical characteristics were extracted from their medical records. Data analyses performed included descriptive statistics, chi-square tests, ANOVA, Kaplan–Meier survival analysis to assess the time to sputum culture conversion and intensive phase treatment outcomes. All statistical analyses were performed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA).

Results: Of 335 patients diagnosed with RMR-TB, 196 (58.51%) were male. A total of 267 patients (79.70%) achieved sputum culture conversion within six months of treatment, whereas 68 patients (20.30%) did not. The overall median time to sputum culture conversion was 35 days (IQR 21 - 59). Significant disparities were observed in the mean duration to sputum culture conversion by HIV status (p= 0.0205). Factors associated with prolonged time to sputum culture conversion included a positive baseline smear (p=0.0097), prior administration of Antiretroviral therapy before tuberculosis diagnosis (p=0.0288), and current antiretroviral use (p=0.0388). The mean time to sputum culture conversion was significantly longer in the low-risk (62.29 ± 10.12 days) and moderate-risk (50.40 ± 7.06 days) groups compared to the high-risk group (32.35 ± 3.03 days) (p = 0.0032). Notably, over 40% of RMR-TB patients experienced suboptimal intensive phase treatment outcomes.

Conclusion: The study findings indicated that patients diagnosed with RMR-TB experience shorter time to sputum culture conversion and have higher rates of unfavourable intensive phase treatment outcomes. This is indicative of the important role rifampicin plays in drug-resistant tuberculosis therapy and the need for special attention and close monitoring of RMR-TB patients during the intensive phase treatment.