Bacterial keratitis in Christchurch, New Zealand, 1997-2001

Purpose: To identify which organisms cause bacterial keratitis in a local community and to determine how patients with suspected bacterial keratitis should be initially treated. Methods: The results of all corneal scrapes performed in the ophthalmology department of Christchurch Hospital between 1997 and 2001 were reviewed. All samples were collected at the 'bedside' by a technician from the microbiology department and were processed immediately. Results: Eighty-seven corneal scrapes were performed on 78 patients. There was a positive Gram stain in 43.7% (38/87) of scrapes. There was a positive culture in 58.6% (51/87) of scrapes. The commonest Gram-positive organisms were coagulase negative Staphylococci (19.4%) and Corynebacterium spp. (16.1%). The commonest Gram-negative organisms were Moraxella spp. (19.4%) and Pseudomonas aeruginosa (3.2%). Every Gram-positive organism was sensitive to chloramphenicol and every Gram-negative organism was sensitive to ciprofloxacin. In contrast, 89% of Gram-negative organisms were sensitive to chloramphenicol and 88% of Gram-positive organisms were sensitive to ciprofloxacin. Conclusion: The results are very different to those reported by other centres. Most notably, a much higher incidence of infection by Corynebacterium spp. and Moraxella spp. and a lower incidence of Pseudomonas aeruginosa was found. In this centre it appears appropriate to initially treat patients with Gram-positive organisms with chloramphenicol and patients with Gram-negative organisms with ciprofloxacin. Patients with a negative Gram stain should be treated with alternating chloramphenicol and ciprofloxacin while awaiting culture results.