One of the pillars of the SAFE strategy for trachoma control is the use of mass drug administration (MDA) using azithromycin (Zithromax®) donated by Pfizer Inc. Azithromycin is very effective for curing infections with ocular Chlamydia trachomatis with a single oral dose. Unusually for the administration of antibiotics, MDA is offered to all members of a defined population without first making an individual diagnosis for each recipient. This is done, in part, because the clinical signs of trachoma do not always mean that C. trachomatis is present and an accurate test for infection is costly and time-consuming to conduct. As a result, members of a defined population (the ‘target population’) are offered treatment whether they have a confirmed current infection or not.