Review of epidemiological features, microbiological diagnosis and treatment outcome of microbial keratitis: Experience of over a decade

Abstract

Purpose:To review the epidemiological characteristics, microbiological profile, and treatment outcome of patients with suspected microbial keratitis.Materials and Methods:Retrospective analysis of a non-comparative series from the database was done. All the patients presenting with corneal stromal infiltrate underwent standard microbiologic evaluation of their corneal scrapings, and smear and culture-guided antimicrobial therapy.Results:Out of 5897 suspected cases of microbial keratitis 3563 (60.4%) were culture-proven (bacterial – 1849, 51.9%; fungal – 1360, 38.2%; Acanthamoeba – 86, 2.4%; mixed – 268, 7.5%). Patients with agriculture-based activities were at 1.33 times (CI 1.16–1.51) greater risk of developing microbial keratitis and patients with ocular trauma were 5.33 times (CI 6.41–6.44) more likely to develop microbial keratitis. Potassium hydroxide with calcofluor white was most sensitive for detecting fungi (90.6%) and Acanthamoeba (84.0%) in corneal scrapings, however, Gram stain had a low sensitivity of 56.6% in detection of bacteria. Majority of the bacterial infections were caused by Staphylococcus epidermidis (42.3%) and Fusarium species (36.6%) was the leading cause of fungal infections. A significantly larger number of patients (691/1360, 50.8%) with fungal keratitis required surgical intervention compared to bacterial (799/1849, 43.2%) and Acanthamoeba (15/86, 17.4%) keratitis. Corneal healed scar was achieved in 75.5%, 64.8%, and 90.0% of patients with bacterial, fungal, and Acanthamoeba keratitis respectively.Conclusions:While diagnostic and treatment modalities are well in place the final outcome is suboptimal in fungal keratitis. With more effective treatment available for bacterial and Acanthamoeba keratitis, the treatment of fungal keratitis is truly a challenge.

Update on the Management of Infectious Keratitis

“…Giemsa has a sensitivity of 40–85% for diagnosing fungal cases. 16–18 Blood and chocolate agar are most commonly used to culture bacteria, while Sabouraud’s agar or potato dextrose are best for isolating fungus, and non-nutrient agar with Escherichia Coli overlay can be used to culture Acanthameoba . Thioglycollate broth is another option to identify aerobic or facultatively anaerobic bacteria, but contaminant is a problem and often it is difficult to determine if isolated organisms are the etiology of infection.…”

Prospective Study of the Diagnostic Accuracy of the In Vivo Laser Scanning Confocal Microscope for Severe Microbial Keratitis

“…Culture-positivity rates in MK vary widely, from 40% to 73% in different settings, most likely because of the small size of corneal-scrape samples, prior antimicrobial treatment inhibiting microbial growth, and the fastidious nature of some organisms requiring special growth media (e.g., fungi and Acanthamoeba ) 4, 5, 6, 7. Direct visualization of fungal filaments or Acanthamoeba cysts in corneal scrapings using light microscopy can give a higher detection rate when compared with culture alone, 8 but it relies on the availability of trained, experienced observers who may not be present in some health care settings.…”

Role of host-defence peptides in eye diseases

“…Fungi are a significant cause of keratitis particularly in warm humid climates and developing countries where they may account for 40% or more of microbial keratitis cases [48, 60-63]. Common culprits are Fusarium solani , Aspergillus fumigatus and Candia albicans [61,63-68].…”

“…Common culprits are Fusarium solani , Aspergillus fumigatus and Candia albicans [61,63-68]. These infections are very difficult treat and are characterized by corneal edema and ulceration leading to scarring, and profound vision loss.…”