Evaluation of tear samples for Herpes Simplex Virus 1 (HSV) detection in suspected cases of viral keratitis using PCR assay and conventional laboratory diagnostic tools

Background Herpes Simplex Virus (HSV) keratitis is a leading cause of corneal blindness. Definitive laboratory diagnosis is essential for timely management. Collection of corneal scrapings in patients with advanced epithelial keratitis and corneal thinning poses perforation risks; tear fluid is a feasible and convenient alternative but has not been widely evaluated for HSV detection. Methods Tear fluid alone (229) or along with corneal scrapings (153) from patients of suspected herpetic keratitis was tested for HSV-1 antigen by indirect immunofluorescence assay, virus isolation in Hep 2 cells and PCR to amplify the 111 bp region of the thymidine kinase (tk) coding gene and the 144 bp region from the DNA polymerase coding gene of HSV. Results HSV 1 antigen was detected in 31/229 (13.53%) tear specimen and 35/153 (22.87%) corneal scrapings in immunofluorescence assay; virus was isolated from 12/229 (5.2%) tear and 17/153 (11.11%) corneal scrapings, and PCR was positive for both the genes in 32/229 (13.97%) tear specimen and 56/153 (36.66%) corneal scrapings. Conclusion Corneal scrapings yielded a significantly better HSV positivity than tears in both the PCR assay (p<0.0005) and immunofluorescence assay. PCR was much more sensitive than immunofluorescence and virus isolation. However, tears should be tested for definitive laboratory diagnosis of HSV infection whenever corneal scraping collection is not possible.