How can herpes simplex be diagnosed when vesicle roofs have come off?

Viral culture is the optimal method for diagnosing herpes simplex virus (HSV) infection, especially when the vesicle roofs have come off. This technique involves swabbing the base of an ulcer or lesion to collect fluid or tissue. Even after the vesicles rupture, the virus can still be isolated from the remaining fluid or cells at the site, making viral culture a reliable option for confirmation of HSV, as it allows for the direct detection of the virus.

Furthermore, viral culture is specific and sensitive for HSV, which is crucial in differentiating it from other herpesviruses. Although other methods such as serologic testing can confirm a past or current infection by detecting antibodies against the virus, they do not provide immediate evidence of an active infection and are less useful in acute settings. Tzanck smear, while historically used, lacks specificity and sensitivity compared to viral culture, as it may show polytypic giant cells that can be seen in other conditions. Skin biopsy, although it can provide diagnostic information, is more invasive and not typically utilized for this purpose in standard practice for herpes infections.

Thus, in cases where vesicles have ruptured, viral culture remains the best approach for diagnosing herpes simplex virus.