Author summary Why was this study done? Though cited in many countries’ national guidance, the evidence that individuals with pulmonary tuberculosis (TB) are rendered non-infectious by 2 weeks of effective TB treatment is challenged. This systematic review was commissioned by the World Health Organization to provide evidence to inform TB infection prevention and control guidelines. We sought to synthesise the available data on the clearance of potentially infectious TB bacteria from the sputum of patients after starting effective treatment. What did the researchers do and find? We performed systematic searches of literature databases to identify relevant articles, using predetermined inclusion criteria. Extracted data were synthesised using narrative summaries and meta-analyses. A minority of patients had clearance of TB bacteria from sputum at 2 weeks of effective treatment, as assessed by either sputum smear or culture. As expected, the proportion having cleared TB bacteria from sputum increased over time; however, at 2 months of treatment 12% and 41% of patients still had viable TB bacteria present, as assessed by solid and liquid culture, respectively. What do these findings mean? The presence of viable TB bacteria in the sputum of pulmonary TB patients beyond 2 weeks of effective treatment suggests individuals may be infectious for longer than this interval. TB transmission requires the presence of viable mycobacteria in sputum and a mechanism for aerosol or droplet spread. Understanding how other factors, such as the presence of cough, change during treatment is also important for TB infection prevention and control.