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 mono-therapy while awaiting culture results.