Bacterial keratitis in Christchurch, New Zealand, 1997-2001

To identify which organisms cause bacterial keratitis in a local community and to determine how patients with suspected bacterial keratitis should be initially treated.

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.

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.

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.