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Comparative Analysis of Bacterial Isolation Rates From Corneal Scrapes and Corneal Impression Membranes in Suspected
Khayam Naderi1, Rebecca Gorton2, Neil Stone3
1Department of Ophthalmology, Moorfields Eye Hospital, London, United Kingdom.
Purpose:
Corneal impression membranes (CIMs) are an easier and safer method to obtain samples in microbial keratitis than corneal scrapes (CS). This study compares the level of agreement in the isolation rates of bacteria using CIM and CS in patients with suspected microbial keratitis.
Methods:
Retrospective review of 116 consecutive patients with suspected microbial keratitis requiring corneal sampling. Both CS and CIM were performed for each case. The level of agreement in microbial isolation rates between the paired samples was compared using Cohen kappa.
Results:
Microorganisms were isolated from 74/116 (63.8%) of CIM samples and in 84/116 (72.4%) of CS samples (P = 0.12). The commonest bacterial isolates were Pseudomonas aeruginosa [20.0% (CIM) vs. 20.7% (CS); P = 0.87] and Staphylococcus species. The commonest coagulase-negative Staphylococcus species were Staphylococcus epidermidis (24.1% vs. 25.9%; P = 0.88) and Staphylococcus warneri (3.4% vs. 7.8%; P = 0.25). Staphylococcus aureus was isolatedin 6.9% versus 7.8% (P = 1.00). There was no isolation of fungi or acanthamoeba in any of the 116 CIM or CS samples. Mixed growth was found in 14.7% of CIM samples and 28.4% of CS samples (P = 0.02). The level of agreement between CIM and CS was 0.89 (P < 0.001) for Pseudomonas aeruginosa, 0.04 (P = 0.71) for Staphylococcus epidermidis, 0.56 (P < 0.001) for Staphylococcus aureus, and 0.11 (P = 0.19) for Staphylococcus warneri.
Conclusions:
CIM is an effective method in collecting corneal samples in patients with suspected microbial keratitis, with a high level of agreement with CS in the isolation of Pseudomonas aeruginosa, and a moderate level of agreement in the isolation of Staphylococcus aureus.
Insights
Corneal impression membranes (CIMs) show high agreement with corneal scrapes (CS) for isolating Pseudomonas aeruginosa and moderate agreement for Staphylococcus aureus in suspected microbial keratitis cases.
Area of Science:
- Ophthalmology
- Microbiology
- Medical Diagnostics
Background:
- Microbial keratitis diagnosis relies on accurate corneal sampling.
- Corneal scrapes (CS) are standard but can be invasive.
- Corneal impression membranes (CIMs) offer a potentially safer alternative.
Purpose of the Study:
- To compare the diagnostic agreement between CIM and CS for bacterial isolation in suspected microbial keratitis.
- To evaluate the efficacy of CIM as a sampling method in clinical practice.
Main Methods:
- Retrospective analysis of 116 patients with suspected microbial keratitis.
- Paired corneal sampling using both CS and CIM for each patient.
- Comparison of microbial isolation rates and agreement using Cohen kappa statistic.
Main Results:
- Microorganisms isolated in 63.8% of CIM samples and 72.4% of CS samples.
- High agreement (kappa=0.89) for Pseudomonas aeruginosa isolation between CIM and CS.
- Moderate agreement (kappa=0.56) for Staphylococcus aureus isolation; low agreement for S. epidermidis.
Conclusions:
- Corneal impression membranes (CIMs) are effective for corneal sample collection in microbial keratitis.
- CIM demonstrates high diagnostic agreement with corneal scrapes (CS) for P. aeruginosa.
- CIM shows moderate agreement with CS for S. aureus, suggesting its utility in diagnosing specific bacterial keratitis.
