Primary orofacial herpes is readily identified by clinical examination of persons with no previous history of lesions and contact with an individual with known HSV-1 infection. The appearance and distribution of sores in these individuals typically presents as multiple, round, superficial oral ulcers, accompanied by acute gingivitis. Adults with non-typical presentation are more difficult to diagnose. Prodromal symptoms that occur before the appearance of herpetic lesions help differentiate HSV symptoms from the similar symptoms of other disorders, such as allergicstomatitis. When lesions do not appear inside the mouth primary orofacial herpes is sometimes mistaken for impetigo, a bacterial infection. Common mouth ulcers (aphthous ulcer) also resemble intraoral herpes, but do not present a vesicular stage.
Genital herpes can be more difficult to diagnose than oral herpes since most HSV-2-infected persons have no classical symptoms. Further confusing diagnosis, several other conditions resemble genital herpes, including lichen planus, atopic dermatitis, and urethritis. Laboratorytesting is often used to confirm a diagnosis of genital herpes. Laboratory tests include: culture of the virus, direct fluorescent antibody (DFA) studies to detect virus, skin biopsy, and polymerase chain reaction (PCR) to test for presence of viral DNA. Although these procedures produce highly sensitive and specific diagnoses, their high costs and time constraints discourage their regular use in clinical practice.
Serological tests for antibodies to HSV are rarely useful to diagnosis and not routinely used in clinical practice, but are important in epidemiological studies. Serologic assays cannot differentiate between antibodies generated in response to a genital versus or an oral HSV infection, and as such cannot confirm the site of infection. Absence of antibody to HSV-2 does not exclude genital infection because of the increasing incidence of genital infections caused by HSV-1.