Diagnosis of Fungal Keratitis in Low-Income Countries: Evaluation of Smear Microscopy, Culture, and In Vivo Confocal Microscopy in Nepal
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Date
2022
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Fungi
Abstract
Clinically diagnosing fungal keratitis (FK) is challenging; diagnosis can be assisted by
investigations including in vivo confocal microscopy (IVCM), smear microscopy, and culture. The
aim of this study was to estimate the sensitivity in detecting fungal keratitis (FK) using IVCM, smear
microscopy, and culture in a setting with a high prevalence of FK. In this cross-sectional study
nested within a prospective cohort study, consecutive microbial keratitis (MK) patients attending a
tertiary-referral eye hospital in south-eastern Nepal between June 2019 and November 2020 were
recruited. IVCM and corneal scrapes for smear microscopy and culture were performed using
a standardised protocol. Smear microscopy was performed using potassium hydroxide (KOH),
Gram stain, and calcofluor white. The primary outcomes were sensitivities with 95% confidence
intervals [95% CI] for IVCM, smear microscopy and culture, and for each different microscopy stain
independently, to detect FK compared to a composite referent. We enrolled 642 patients with MK;
468/642 (72.9%) were filamentous FK, 32/642 (5.0%) were bacterial keratitis and 64/642 (10.0%) were
mixed bacterial-filamentous FK, with one yeast infection (0.16%). No organism was identified in
77/642 (12.0%). Smear microscopy had the highest sensitivity (90.7% [87.9–93.1%]), followed by
IVCM (89.8% [86.9–92.3%]) and culture (75.7% [71.8–79.3%]). Of the three smear microscopy stains,
KOH had the highest sensitivity (85.3% [81.9–88.4%]), followed by Gram stain (83.2% [79.7–86.4%])
and calcofluor white (79.1% [75.4–82.5%]). Smear microscopy and IVCM were the most sensitive
tools for identifying FK in our cohort. In low-resource settings we recommend clinicians perform
corneal scrapes for microscopy using KOH and Gram staining. Culture remains an important tool to
diagnose bacterial infection, identify causative fungi and enable antimicrobial susceptibility testing.
Description
Keywords
Microbial keratitis, Fungal keratitis, In vivo confocal microscopy, Diagnosis, Microbiology, Nepal, Cornea, Culture, Microscopy
Citation
Hoffman, J.J.; Yadav, R.; Sanyam, S.D.; Chaudhary, P.; Roshan, A.; Singh, S.K.; Arunga, S.; Hu, V.H.; Macleod, D.; Leck, A.; et al. Diagnosis of Fungal Keratitis in Low-Income Countries: Evaluation of Smear Microscopy, Culture, and In Vivo Confocal Microscopy in Nepal. J. Fungi 2022, 8, 955. https://doi.org/ 10.3390/jof8090955