Spectrum of mycotic keratitis and their antifungal susceptibility pattern in a tertiary care hospital, Chennai

INTRODUCTION: One of the predominant causes of blindness in the developing world is keratitis causing prolonged morbidity. Mycotic keratitis is an important ophthalmological problem, especially in outdoor workers in the tropics. In different studies conducted in various parts of India, it accounts for 6 to 50% of all cases of keratitis. Trauma with vegetable matter or organic matter or soil, indiscriminate use of topical antibiotics and topical corticosteroids are the predominating cause of keratitis. For clinical purpose, the corneal smear result is more important as it allows the determination of initial therapy. Timely diagnosis and aggressive early treatment can prevent sight threatening complications caused by keratitis. Standardized antifungal susceptibility tests have become essential tool to guide the treatment of mycotic keratitis. The purpose of this study is to identify, isolate and do antifungal susceptibility of obtained fungal isolates in patients with mycotic keratitis in a tertiary care hospital, Chennai. MATERIALS AND METHODS: In the present cross sectional study, Corneal scrapings from 100 patients with clinically suspected mycotic keratitis were obtained by Bard Parker knife / surgical blade no.15 from base to edge of ulcer as much as possible under aseptic precautions after instilling 4% xylocaine under slit lamp examination by an Ophthalmologist. One part of scrapings was used for direct microscopic examination by subjecting it to10% KOH wet mount and Grams staining to identify fungal elements. Other part of scrapings is used for culture in two Sabouraud Dextrose agar (SDA) without cycloheximide but containing Gentamycin 10 μg /ml and kept in room temperature at 27oc and at 37oc for 2 to 8weeks, but observed daily. Initial growth was usually observed within 3 days to 1 week. Growth obtained was stained with lactophenol cotton blue and identified by it’s morphology. All isolates were subjected to antifungal susceptibility tests by micro broth dilution tests. Collected data were be analysed statistically. RESULTS: A total of 100 patients with clinically suspected mycotic keratitis were included in the study and 35 (35%) out of 100 fungal isolates were identified and isolated. Patients with the age group between 41 – 50 years (43%) were commonly affected. Male preponderence was seen in this study of mycotic keratitis (74.3%). Incidence of fungal keratitis was more in the rural than urban population (66%). Majority of the patients were agricultural labourers (54.29%). Trauma with vegetative matter was found to be the common predisposing factor (68.5%) in the development of mycotic keratitis. Majority of isolates belonged to the genus Aspergillus spp (74%) followed by Fusarium spp (17%) and Curvularia spp (9%). The frequently isolated pathogen among the genus Aspergillus was Aspergillus fumigatus (40%) followed by Aspergillus niger and Aspergillus terreus. The sensitivity of 10% KOH mount was found to be 91%. The specificity of KOH preparation was 77%. The positive predictive value of KOH preparation was 68%. The negative predictive value of KOH preparation was 79%. In antifungal susceptibility by Broth Micro dilution method, Amphotericin B showed MIC ≤2μg/ml in 33(94.2%), which was a significant finding among 35 fungal isolates. Voriconazole showed MIC ≤2μg/ml in 31(88.5%) out of 35 fungal isolates. Itraconazole showed MIC ≤ 2μg/ml in 23 (66%) out of 35 fungal isolates. Fluconazole showed MIC ≤2μg/ml in 10 (28.5%) out of 35 fungal isolates. Fluconazole showed MIC ≥ 2μg/ml in 25 (71.3%) of the fungal isolates. Compared to Fluconazole, the MIC for Amphotericin B, voriconazole, Itraconazole was low. CONCLUSION: Fungal keratitis is one of the most important cause of preventable blindness in the developing world. It was predominant in males of rural background with vegetative matter induced ocular trauma as the major predisposing factor. A simple 10% KOH mount preparation was highly beneficial as rapid screening test for diagnosis. Among the isolates, Aspergillus spp were the most common agent causing mycotic keratitis. From the study, the vital role of microbiological evaluation in the management of mycotic keratitis is clearly evident, since the clinical features alone are not adequate to confirm infection. The clinicians and microbiologists should work hand in hand to prevent blindness due to mycotic keratitis. The awareness among the public about the ocular hygiene and protection from occupational hazard needs to be emphazied along with their early visit to the hospital in case of any ocular trauma and disease.