Comparison of Nested PCR and Culture Identification of
Pythium insidiosum in Patients with Pythium Keratitis
Panida Kosrirukvongs MD*, Angkana Chaiprasert MD**,
Chayamon Canyuk MD*, Wanchai Wanachiwanawin MD***
Affiliation :
* Department of Ophthalmology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
** Department of Microbiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
*** Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Background : Delayed diagnosis can lead to the development of endophthalmitis and blindness, which is difficult to manage
because of the lack of an effective antimicrobial agent.
Objective : Comparing the nested polymerase chain reaction (PCR) technique with the standard diagnostic culture method
for Pythium insidiosum.
Material and Method: Eighty-three patients with suspected fungal keratitis were enrolled in this observational, cross-
sectional study from the Faculty of Medicine Siriraj Hospital between February 2011 and February 2014. Patient symptoms,
associated diseases, duration of ulcers, precipitating causes, best-corrected visual acuity, intraocular pressure, and other
clinical findings were recorded. Corneal scrapings were taken for Gram staining, bacterial and fungal cultures, staining
with potassium hydroxide preparation, and DNA extraction for nested PCR. The sensitivity, specificity, accuracy, and
agreement of the nested PCR analysis and culture diagnosis of P. insidiosum were compared.
Results : Five patients had a positive result for nested PCR amplification of P. insidiosum, while only one of these was also
positive for culture growth of Pythium. Nested PCR sensitivity was 50% (95% confidence interval [95% CI] 1.3-98.7),
specificity 94.7% (95% CI 86.9-98.5), and accuracy 93.5% (95% CI 85.7-97.2) with a fair agreement (kappa 0.258, p =
0.011).
Conclusion : Therefore, nested PCR may be an appropriate test for P. insidiosum in diagnosing Pythium keratitis with high
accuracy, despite small amounts of corneal specimen.
Keywords : Accuracy, Nested PCR, Pythium insidiosum keratitis, Sensitivity, Specificity
All Articles
Download