Our results show that the sensitivities of the SV and TC techniques are comparable (83.3%) and suitable for the isolation of HSV-1 using corneal scrapings for the laboratory diagnosis of HSK. Sensitivity of SV has been reported to be in the range of 70–98% in comparison with TC in the isolation of HSV . We found no difference in the sensitivity of these two techniques, suggesting that both techniques can be used for the laboratory diagnosis of HSK using corneal scrapings.
There are a number of studies comparing these two techniques and other techniques as well for the detection of HSV infections [6, 8, 11, 12] with varied results. This may be attributed to the variety of specimens processed, time of collection of specimens, sample collection method, disease pathogenesis and the cell line employed. To the best of our knowledge based on a MEDLINE search, there are no reports comparing the sensitivities of a 24 h SV and the TC, especially for the diagnosis of HSK using corneal scrapings.
As mentioned earlier, HSK is a potentially blinding ocular infection warranting a prompt antiviral therapy. Towards this end, we chose a 24 h SV, since a confirmatory report can be provided the next day following the day of specimen collection (approximately within 3 Oh). Tube cultures were terminated the fifth day since our earlier observations (unpublished data) showed that more than 95% of our virus strains were isolated from cases of HSK in less than five days in TC using either vero/A549/HEp2 or BHK 21 cells. We preferred to use vero cells since our experience suggested that this cell line performed better than the others we had used (over a two-year period) for the isolation of HSV-1 from cases of HSK.
A study by Walpita et al. showed that the shell vial assay was more sensitive than the conventional tube culture for the detection of HSV from ocular infections  using conjunctival swabs. The details of various ocular infections (Keratitis, conjunctivitis, keratouveitis etc.) they have included in their study have not been provided. These authors have considered the results of a 48 h SV and the TC were processed for 21 days. Our results cannot be directly compared with that of these authors. Nevertheless, both the studies suggest that SV is a suitable alternative to TC for the isolation of HSV. Further, our study confirms that SV can be employed for the diagnosis of HSK, especially using corneal scrapings. We believe that corneal scraping is a more suitable specimen than conjunctival swab for the laboratory diagnosis of HSK, since a large number of cells can be collected by scraping.
The rate of isolation of HSV-1 in our study was only 32.3% while the viral antigen detection assay was more sensitive (72.9%). However, this technique has its own disadvantages including false positivity. In general, the rates of isolation of HSV-1 in cultures from corneal specimens have been low , irrespective of the cell line used. A recent study has reported that isolates from herpetic keratitis grow better in corneal epithelial cells and rabbit corneal epithelial cells may be more suitable for isolating HSV from the cornea . Employing such cell lines of corneal origin may prove beneficial in improving the rates of HSV-1 isolation for the laboratory diagnosis of HSK. Such studies are being done in our laboratory using a recently described immortalized human corneal epithelial cell line employing the shell vial assay .
In conclusion, our data suggest that in comparison to TC which is cumbersome, expensive and time consuming, SV is a rapid culture assay, is much simpler, easy to perform and economical for the isolation of HSV-1 from corneal scrapings, for a confirmatory laboratory diagnosis of HSK.