Background Tuberculosis (TB) remains one of the most common causes of death from an infectious disease. Late sputum culture conversion among Multi-Drug Resistant Tuberculosis (MDR-TB) patients poses a risk for poor treatment outcomes. The study aimed to determine the incidence and factors associated with late sputum culture conversion among MDR- TB patients on treatment at the tuberculosis (TB) unit of Mulago National Referral Hospital. Methods A retrospective cohort study of 255 MDR-TB patient records between January 1st 2012 to December 31st 2018 were reviewed. Consecutive sampling was employed. Demographic characteristics, clinical factors and social factors were studied. STATA version 15 was used for analysis. Incidence was calculated as the ratio of MDR -TB patients with late sputum culture conversion result to the total number of participants studied. Factors associated were evaluated using generalized linear model (GLM) with Poisson family and log link using robust standard errors to adjust for over inflated variances. Results The incidence of late sputum culture conversion was 32% (95% CI 26.3- 37.8). increasing age in years (incidence rate ratio IRR 1.004, 95%CI 1.000 1.008, P value 0.044), increasing weight (IRR 0.995, 95% CI 0.991- 0.999, P value 0.020) and 9-12 months multi drug tuberculosis MDR-TB regimen (IRR 0.893, 95% CI 0.805- 0.989, P value 0.030) were factors associated with late sputum culture conversion. Conclusions: The incidence of late sputum culture conversion among MDR-TB patients on treatment was high (32%), occurring in about three out of every ten patients. Increasing weight, increasing age and 9-12 months MDR-TB drug regimen were significantly associated. Isolation of patients for a minimum of two months to minimize community transmission, starting eligible patients on the 9-12months MDR-TB regimen and categorization of patients into high-risk groups (elderly and underweight) with special targeted packages. Background Tuberculosis (TB) remains one of the most common causes of death from an infectious disease worldwide (Murray et al., 2014). In 2019, an estimated 3.3% of new TB cases and 18% of previously treated cases had MDR/RR-TB equivalent to an estimated 465 000 (range, 400 000– 535 000) incident cases of rifampicin resistant TB; 78% had multidrug resistant TB (WHO, 2020).

The authors have declared no competing interest.

NO -The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Permission to the study and Letter for waiver of consent to use the tuberculosis unit register was granted by Makerere University Clinical Epidemiology Unit. Ethical approval from School of Medicine Research and Ethics Committee (SOMREC) and Mulago national referral hospital administrative approval.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes