Microbial keratitis in Waikato, New Zealand.

Background: Bacterial keratitis is a potentially sight-threatening condition. This study is performed to identify the common causative organisms for bacterial keratitis in Waikato region and the antibiotic sensitivities to these organisms.

Design: Retrospective, observational, case series.

Participants: The microbiology records of all patients with bacterial keratitis who presented to the Ophthalmology department, Waikato Hospital, New Zealand between January 2003 and December 2007.

Methods: The corneal scrape results were reviewed. Antibiotic sensitivity for the organism was tested following National Committee for Clinical Laboratory Standards (NCCLS) method.

Main Outcome Measures: In vitro laboratory susceptibility testing of ocular isolates to various antibiotics.

Results: A total of 265 scrapes were performed. Gram stain was positive in 35 (13.2%) eyes. Positive culture was seen in 174 (65.6%) scrapes; 78.2% were Gram-positive and 20.2% were Gram-negative organisms. Most common Gram-positive organisms were coagulase-negative Staphylococci (40.8%) and Staphylococcus aureus (11.5%). Most common Gram-negative organisms were Moraxalla species (8.0%) and Pseudomonas aeroginosa (3.4%). Of the bacterial organisms 99% were sensitive to ciprofloxacin. All Gram-negative organisms and 95.5% Gram-positive organisms were sensitive to tobramycin; 96.6% Gram-positive organisms and 98.3% Gram-negative organisms were sensitive to cefuroxime.

Conclusions: Our results are comparable to other regions in New Zealand but the incidence of coagulase-negative Staphylococcus is much higher in this region compared with other New Zealand studies. It seems appropriate to start patients with corneal ulcers initially on fluoroquinolone monotherapy while awaiting culture results.