12-year analysis of the microbiological profile of infectious keratitis (IK) in Cork, Ireland

To determine the frequency and causative pathogens of infectious keratitis (IK) at Cork University Hospital, Ireland.

A retrospective review was performed of IK cases undergoing corneal scraping / swabs between 2010-2022. Specimens were identified from the laboratory information system. Microbiological profiles were analysed using culture and/or polymerase chain reaction (PCR) testing for Acanthamoeba, herpes simplex virus (HSV), and varicella zoster virus (VZV).

A total of 319 specimens from 288 patients were analysed (mean age 52.0 ± 25.6 years). Overall, 189 specimens (60%) were culture positive. Polymicrobial growth was identified in 48 cases (15%). Of 198 isolates, the most frequently identified organisms were coagulase-negative staphylococci (33%), Staphylococcus aureus (17%), Pseudomonas aeruginosa (12%), Streptococcus pneumoniae (8%), and Gram-negative bacilli (8%). Fungal pathogens accounted for 4% of isolates, while mixed skin flora was reported in 8%. Gram staining was performed on 105 samples, with 22 positive results-68% were concordant with culture. Viral PCR testing was performed on 48 samples, identifying HSV-1 in 5 cases (10%) and VZV in 2 cases (4%). Acanthamoeba testing was performed on 387 specimens from 319 patients, with Acanthamoeba spp. detected in 33 cases (10%).

This is the largest study describing the microbiological profile of IK in Ireland. A high culture-positive rate (60%) with a high rate of isolation of multiple organisms (15%) were observed, likely influenced by skin commensal contaminants such as coagulase-negative Staphylococci. The proportion of Pseudomonas aeruginosa (12%) was lower than expected. No significant antimicrobial resistant isolates were identified, supporting current empiric antimicrobial treatment strategies.