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Journal of Clinical Microbiology, May 2009, p. 1314-1318, Vol. 47, No. 5
0095-1137/09/$08.00+0     doi:10.1128/JCM.00173-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Laboratory Diagnosis of Amoebic Keratitis: Comparison of Four Diagnostic Methods for Different Types of Clinical Specimens{triangledown}

Andrea K. Boggild,1,{dagger}* Donald S. Martin,2,{dagger} Theresa YuLing Lee,2 Billy Yu,2 and Donald E. Low2,3,4

Tropical Diseases Unit, Toronto General Hospital, Toronto, Ontario, Canada M5G 2C4,1 Parasitology Laboratory, Ontario Agency for Health Protection and Promotion, Etobicoke, Ontario, Canada M9P 3T1,2 Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada,3 Department of Microbiology, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X54

Received 27 January 2009/ Returned for modification 9 March 2009/ Accepted 16 March 2009

Amoebic keratitis causes significant ocular morbidity in contact lens wearers. Current diagnostic methods for amoebic keratitis are insensitive and labor-intensive and have poor turnaround time. We evaluated four laboratory methods for detection of acanthamoebae in clinical specimens. Deidentified, delinked consecutive specimens from patients with suspected amoebic keratitis were assayed for acanthamoebae by direct smear analysis, culture, and PCR using two different primer sets specific for Acanthamoeba ribosomal DNA. The consensus reference standard was considered fulfilled when the results for any two of the four tests were positive, and the outcome measures were sensitivity and specificity. Of 107 specimens assayed over an 18-month period, 20 were positive for acanthamoebae. The sensitivity and specificity of each assay were as follows, respectively: for smear analysis, 55% (95% confidence interval [CI], 33.2 to 76.8%) and 100%; for culture, 73.7% (95% CI, 54.4 to 93.0%) and 100%; for PCR using Nelson primers, 90% (95% CI, 76.9 to 100%) and 90.8% (95% CI, 84.7 to 96.9%); and for PCR using JDP primers, 65% (95% CI, 44.1 to 85.9%) and 100%. Nelson primer PCR demonstrated a single-organism level of analytic sensitivity. The performance characteristics of the assays varied by specimen type, with contact lenses and casings showing the highest rates of detectable acanthamoebae and the highest diagnostic sensitivities for direct smear analysis, culture, and JDP primer PCR, though these results are based on small numbers and should be interpreted cautiously. These findings have important implications for clinicians collecting diagnostic specimens and for diagnostic laboratories, especially in outbreak situations.

* Corresponding author. Mailing address: Tropical Diseases Unit, Toronto General Hospital, 200 Elizabeth Street, North Wing, 13th Floor, Room 1350, Toronto, Ontario, Canada M5G 2C4. Phone: (416) 340-3675. Fax: (647) 439-0827. E-mail: andrea.boggild{at}utoronto.ca

{triangledown} Published ahead of print on 25 March 2009.

{dagger} A.K.B. and D.S.M. contributed equally.

Journal of Clinical Microbiology, May 2009, p. 1314-1318, Vol. 47, No. 5
0095-1137/09/$08.00+0     doi:10.1128/JCM.00173-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Dua, H. S., Aralikatti, A., Said, D. G. (2009). Rapid diagnosis of Acanthamoeba keratitis. Br J Ophthalmol 93: 1555-1556 [Full Text]  


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