Optimal tuberculosis case detection by direct sputum smear microscopy: how much better is more?

Reading more than 100 fields per smear or examining a third sputum has insufficient marginal returns to justify the workload. Examining morning samples only is more efficient, and their collection does not necessarily inconvenience patients. Treatment can be started on the basis of one positive smear. Provided that a well functioning system of smear-microscopy quality control is in place, we propose a strategy based on examination of two morning sputum samples for negative suspects, with the diagnosis based on a single positive result.