Time to Detection in Culture Supports Prediction of Low Transmissibility of Tuberculosis and Discontinuation of Isolation for Low-Risk Patients With A Single AFB-Negative and NAAT-Negative Respiratory Specimen

Abstract

For 94 patients with culture-positive pulmonary tuberculosis, time-to-detection (TTD), acid-fast bacilli (AFB) smear, and nucleic acid amplification test (NAAT) results were reviewed. All 12 patients whose first specimen was negative by AFB smear and NAAT had prolonged TTD, indicating low transmissibility and supporting discontinuing isolation for low-risk patients.Infect Control Hosp Epidemiol 2018;39:619-621.

Time to Detection of Growth for Mycobacterium tuberculosis in a Low Incidence Area

“…In this study, TDG exceeded the 4-5 week duration reported by several authors as sufficient for identifying all culture positive samples (Pfyffer and Wittwer, 2012;Tyrrell et al, 2012;Ogwang et al, 2015;Khan et al, 2018). Indeed, 90 th centile for TDG of all samples was 55 days, and even 58 days in smear negative cases.…”

“…The rationale of this selection of samples was as follows: 1/large scale implementation of Xpert/MTB-RIF has increased same-day diagnosis, with a diagnostic sensitivity exceeding 80% in culture positive samples, irrespective of microscopy ( Boehme et al, 2011 ; Khan et al, 2018 ); 2/in patients who do not have a same-day diagnosis by Xpert/MTB-RIF (negative test or not performed because of sample size), and who will eventually become culture positive, TDG determines when a diagnosis MTB can either be confirmed (as well as drug sensitivity profile), or reasonably excluded (treatment will most often have been started based on clinical suspicion). Our focus was therefore on TDG for all culture positive clinical samples fulfilling these criteria.…”

“…TDG is inversely correlated with number of acid-fast bacilli (AFB) on sputum smears ( Perrin et al, 2007 ; Bark et al, 2011 ; Olaru et al, 2014 ), number of colony forming units in sputum specimens ( Diacon et al, 2014 ) and risk of relapse after therapy in clinical trials ( Bark et al, 2012 ). Baseline TDG is also correlated to time to conversion ( Visser et al, 2012 ) and inversely related to transmissibility ( Khan et al, 2018 ). TDG in treatment-naïve subjects are, as expected, lower in smear positive and NAAT positive subjects ( Khan et al, 2018 ) with median values ranging between 5 ( Bisognin et al, 2020 ; Ma et al, 2020 ) and 23 days ( Boehme et al, 2011 ; Bark et al, 2012 ; Pfyffer and Wittwer, 2012 ; Tyrrell et al, 2012 ; Visser et al, 2012 ; Olaru et al, 2014 ; Ogwang et al, 2015 ; Diriba et al, 2017 ; Khan et al, 2018 ; Zhao et al, 2019 ).…”

“…Baseline TDG is also correlated to time to conversion ( Visser et al, 2012 ) and inversely related to transmissibility ( Khan et al, 2018 ). TDG in treatment-naïve subjects are, as expected, lower in smear positive and NAAT positive subjects ( Khan et al, 2018 ) with median values ranging between 5 ( Bisognin et al, 2020 ; Ma et al, 2020 ) and 23 days ( Boehme et al, 2011 ; Bark et al, 2012 ; Pfyffer and Wittwer, 2012 ; Tyrrell et al, 2012 ; Visser et al, 2012 ; Olaru et al, 2014 ; Ogwang et al, 2015 ; Diriba et al, 2017 ; Khan et al, 2018 ; Zhao et al, 2019 ). A few recent studies suggest that, in the majority of clinical samples, growth of MTB could be detected within 28 days of incubation ( Pfyffer and Wittwer, 2012 ; Ogwang et al, 2015 ).…”