Microbiological diagnosis of infective keratitis: comparative evaluation of direct microscopy and culture results

Abstract

Aims: To determine the sensitivity, specificity and predictive values of potassium hydroxide (KOH) wet mount, Gram stain, Giemsa stain and Kinyoun's acid-fast stain in the diagnosis of infective keratitis. Methods: A retrospective analysis of all patients with clinically diagnosed infective keratitis presenting between September 1999 and September 2002 was carried out. Corneal scrapes were taken and subjected to direct microscopy and culture. Results: 3298 eyes of 3295 consecutive patients with infective keratitis were evaluated, of which 1138 (34.51%) eyes had fungal growth alone, 1069 (32.41%) had bacterial growth alone, 33 (1%) had Acanthamoeba growth alone, 83 (2.5%) had mixed microbial growth and the remaining 975 (29.56%) had no growth. The sensitivity of KOH wet mount was higher (99.3%; 95% confidence interval (CI) 98.6 to 99.6) in the detection of fungi, 100% (95% CI 90.4 to 100) in the detection of Nocardia and 91.4% (95% CI 75.8 to 97) in the detection of Acanthamoeba) than that of Gram-stained smears (89.2% (95% CI 87.3 to 90.8) in fungi, 87% (95% CI 73.0 to 94.6) in Nocardia and 60% (95% CI 42.2 to 75.6) in the detection of Acanthamoeba) in the detection of fungi, Nocardia and Acanthamoeba. 1764 of 3295 (53.54%) patients presented more than 7 days after onset of illness and 84.69% of the eyes had corneal ulcers with size .2 mm in diameter. Positivities of KOH (44.46%; p,0.001) and Gram-stained smears (77.37%; p,0.001) were found to be higher among eyes with larger ulcers (.2 mm) than among eyes with smaller ulcers (,2 mm). Conclusion: KOH smear is of greater diagnostic value in the management of infective keratitis, and it is recommended in all clinics without exception for establishing timely treatment.

PCR-RFLP as a useful tool for diagnosis of invasive mycoses in a healthcare facility in the North of Brazil

“…The identification of H. capsulatum is undoubtedly the most time consuming with cultivation requiring, on average 25 d to develop visible growth. Subsequent identification is micro morphological, confirmatory assay identification (pleomorphism test) may take over 25 d [7,8,18]. An attractive possibility for the use of PCR-RFLP, therefore, consists in the identification of colonies obtained from clinical samples.…”

“…The MALDI-TOF technique is being used as an alternative to precocious identification of fungal species; however, it is still not a reality in Brasil [5,6]. To overcome these limitations, molecular approaches can be used for the detection and identification of pathogenic fungi [7,8].…”

Fungal Corneal Ulcers: A Prospective Study on the Causative Fungus and the Response to the Present Treatment Protocol

“…20 Various studies revealed the utility of KOH preparation in fungal corneal ulcers. 8,18,20,21,22 The sensitivity of KOH preparation has been found to be variable ranging between 33-94% as reported by various studies. The sensitivity and specificity of KOH preparation in our study was 45.45% and 75% respectively.…”

Evaluation of Intracameral Amphotericin B in the Management of Fungal Keratitis: Randomized Controlled Trial

“…For various reasons, the positivity of smears is always higher compared with that of cultures. [17][18][19] The sensitivity of KOH preparation has been reported to range from 94.3% to 100%. 8,19,20 These studies recommend that all smear-positive cases of mycotic keratitis be treated accordingly, despite negative culture reports.…”