The incidence of fungal keratitis in Zagazig University Hospitals, Egypt and the value of direct microscopy and PCR technique in rapid diagnosis

Abstract

Objective: To determine the frequency and risk factors of fungal keratitis (FK) and the value of direct microscopy and PCR techniques of corneal smears as appropriate diagnostic methods. Methods: The keratitis cases in Ophthalmology Department of Zagazig University Hospitals, between January and June 2012 were enrolled. Corneal samples were examined by direct microscopic examination of wet mount preparation with KOH (10%), PCR technique and cultured simultaneously. The corneal smear and PCR findings were compared to the culture results to analyze specificity, sensitivity and predictive values of these techniques. Results: A total of 350 patients diagnosed as keratitis and 60 of them were included in the study by a systemic random sampling method. The FK was proven in 33 (55%) cases with culture results. Ocular trauma (63.6%) was the most prevalent predisposing factor. The cultures revealed that the most frequent fungal pathogen were Penicillium spp. (24.2%) followed by Aspergillus fumigatus (21.2%). Direct microscopic examination had a sensitivity of 100%, specificity of 66.7%, a positive predictive value (PPV) of 78.6% and a negative predictive value (NPV) of 100%. PCR had a sensitivity of 100%, specificity of 88.9%, a PPV of 91.7% and a NPV of 100%. Conclusion: Although, PCR is able to detect fungi in a high proportion of culture negative cases, it is difficult to be used as a routine diagnostic test due to the economic reasons. Therefore, we strongly recommend the use of direct microscopy of corneal smear as a rapid, economic and sensitive method for screening of FK.

Keywords

• Fungal keratitis, incidence, predisposing factors, rapid diagnose, direct microscopy, PCR

The incidence of fungal keratitis in Zagazig University Hospitals, Egypt and the value of direct microscopy and PCR technique in rapid diagnosis

Öz

Amaç: Fungal keratit (FK) sıklığının, risk faktörlerinin ve korneal örneklerin direkt mikroskopi ile incelenmesi ve PCR tekniğinin tanı değerinin araştırılması.Yöntemler: Mısır’da, Zagazig Üniversitesi Hastaneleri Göz Hastalıkları Departmanı’nda Ocak-Haziran 2012 arasında keratit tanısı alan hastalar çalışmaya alındı. Korneal örnekler %10 KOH preparasyon yöntemi ile direkt mikroskopi ile incelendi, ayrıca örnekler PCR ile fungal DNA varlığı açısından test edildi vekültür plaklarına ekim yapıldı. Korneal smear direkt mikroskopi ve PCR bulguları kültür sonuçları ile testlerin duyarlılığı, güvenirliği, uygunluğu ve tahmin değerleri açısından karşılaştırıldı.Bulgular: Çalışma süresince toplam 350 hasta keratit olarak değerlendirilerek bunlardan 60 tanesi rastgele örnekleme yöntemiyle çalışmaya dâhil edildi. Toplam 60 hastanın 33’ünde (% 55,0) kültürde fungus üremesi ile FK tanısı doğrulandı. Göz travması en sık predispozan faktör olarak değerlendirildi (% 63,6). En sık fungal ajan Penicillium spp. idi (% 24,2) ve bunu Aspergillus fumigatus (% 21,2) takip etti. Direkt mikroskopinin FK tanısında duyarlılığı % 100, özgüllüğü %66,7, pozitif tahmin değeri (PPV) % 78,6 ve negatif tahmin değeri (NPV) % 100 olarak hesaplandı. PCR tekniğinin ise duyarlılığı % 100, özgüllüğü % 88,9, PPV % 91,7 ve NPV % 100 olarak hesaplandı.Sonuçlar: FK tanısında PCR, kültür negatif olgularda önemli oranda fungal etiyolojiyi gösterebilmesine rağmen, pahalı olması sebebiyle FK tanısında rutin tanısal test yöntemi olarak kullanılamayacağını, bunun yerine daha ekonomik, daha hızlı ve duyarlı bir yöntem olan korneal örneklerin direkt mikroskopik incelemesinin daha uygun olduğunu düşünüyoruz

Anahtar Kelimeler

• Fungal keratit, insidans, predispozan faktörler, hızlı tanı, direkt mikroskopi, PCR

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