Customised 96-ocular TaqMan (iCAM) microarray PCR card for rapid diagnosis of microbial keratitis

Abstract

Aim To validate the diagnostic performance of a custom 96-micro-organism TaqMan PCR card (iCAM) for microbial keratitis (MK) from a single corneal epithelial sample.Methods Patients over the age of 18 referred to Cambridge University Hospital with MK were recruited in this single-site prospective cohort study between September 2021 and January 2023. An ocular-specific, customised microarray card (iCAM) was constructed according to primer and probe nucleotide sequences developed in our department to detect bacteria, viruses, Acanthamoeba and fungi commonly implicated in MK using a single corneal epithelial sample. Part of the corneal epithelial sample was taken for conventional cultures per local protocol, followed by iCAM array. Microbial detection rate and positive predictive value (PPV) were evaluated.Results 38 corneal epithelial samples from 32 patients with MK and 4 control samples from healthy participants were obtained from 36 consecutive patients. A causative microbe was isolated in 15/34 samples (44%) using the iCAM test, compared with 15 by conventional methods (44%). iCAM test processing time varied between 6 and 24 hours compared with up to 7 days for conventional tests. Combined, the microbial detection rate was 65%, with the correlation between methods at 62%. The iCAM test could detect all major micro-organism groups with 56% sensitivity and 60% PPV.Conclusions The iCAM test can detect bacterial, fungal, viral and protozoan organisms using one corneal epithelial sample. The limitations include small patient cohort size and reduced volume of available corneal epithelial sample when shared between the iCAM PCR test and conventional culture methods utilised in the study. A multicentre trial is being planned to validate the clinical impact of using iCAM test on accuracy of diagnosis, early institution of appropriate antimicrobials and clinical outcomes.Trial registration number ISRCTN17422545.