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J. Freidlin, N. Acharya, V. Cevallos, T. P. Margolis; Does Asymptomatic Shedding of HSV on the Ocular Surface Lead to False Positive PCR Lab Testing?. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4749.
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As assayed by polymerase chain reaction (PCR), Kaufman et al (IOVS 2005) recently reported an unexpectedly high rate of herpes simplex virus (HSV) shedding on the ocular surface of patients without active corneal disease. In light of this, we reviewed our clinical lab experience for evidence of an unexpectedly high rate of false positives in a CLIA-certified PCR-based assay of corneal scrapings used to diagnose HSV infection.
We identified all corneal specimens in our clinical laboratory database that were tested for HSV DNA by PCR from August 1, 2000 to October 31, 2006. Our assay amplifies a highly conserved 179 base pair region of HSV-1 and HSV-2 DNA polymerase. Amplified viral DNA is detected by ethidium bromide stained gel electrophoresis and confirmed by restriction digest with AciI. Assay sensitivity is between 10 and 100 copies of the viral genome. The charts of all patients that tested positive for HSV DNA were reviewed to determine the clinical findings and medication use at the time of sample collection. Patients were considered to have a clinical picture consistent with HSV infection if any two of the following were present: typical dendritiform or geographic epithelial lesions, interstitial keratitis, neurotrophic cornea, endotheliitis, iridocyclitis, or response to antiviral medications.
Out of 206 corneal tissue samples, 23 (11.2%) tested positive for HSV DNA by PCR. Of these 23 patients, 22 (95.7%) were judged to have a clinical presentation typical of HSV infection. The remaining patient presented late in the course of her disease with atypical necrotizing keratitis, failed to respond to antiviral medications, and went on to perforation. Nine of the 23 patients (39.1%) who tested positive were taking antiviral medications at the time their corneas were sampled.
In our CLIA-certified clinical lab, positive test results for HSV DNA predict a clinical picture consistent with HSV corneal infection. These data suggest that asymptomatic ocular shedding of HSV does not contribute to an unacceptable rate of false positive results when testing is performed with a properly calibrated PCR-based assay.
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