The objective of the study was to identify the extent and cause of an outbreak of epidemic keratoconjunctivitis (EKC). The study design was active case finding and a case-control study of clinic patients who developed symptoms of EKC between 31 December 2005 and 31 March 2006. The main outcome measures were clinical procedures carried out and clinicians seen during clinic visit. Significantly more cases than controls had tonometry with instillation of anaesthetic drops (OR 16·5, 95% CI 3·9–145·1, P<0·01), optical coherence tomography (OR 4·7, 95% CI 1·2–21·9, P=0·01), or instillation of dilating drops by an orthoptist (OR 2·3, 95% CI 1·1–4·7, P=0·01). Significantly more cases than controls were seen by one orthoptist (OR 21·8, 95% CI 8·2–60·0, P<0·01). Transmission of EKC within the clinic was probably due to contamination of either or both the anaesthetic drops and the tonometer head in the room used by an orthoptist. A comprehensive suite of strategies is required to prevent healthcare-associated EKC.