Clinical utility of a nested nucleic acid amplification format in comparison to viral culture for the diagnosis of mucosal herpes simplex infection in a genitourinary medicine setting

BACKGROUND Nested nucleic acid amplification tests are often thought too sensitive or prone to generating false positive results for routine use. The current study investigated the specificity and clinical utility of a routine multiplex nested assay for mucosal herpetic infections. METHODS Ninety patients, categorised into those clinically diagnosed to (a) have and (b) not have herpetic infection, were enrolled. Swabs from oral and ano-genital sites were assayed by the nested assay and culture and the results assessed against clinical evaluation for diagnosing herpetic infections; cell content was also recorded. RESULTS Twenty-six and 64 patients were thought to (a) have and (b) not have mucosal herpetic infection. Taking the clinical evaluation as indicating the presence of herpetic infection, the nested polymerase chain reaction and culture had respective sensitivities of 19/26 (73%) and 12/26 (46%) (Chi2 p = 0.02). There was no significant difference in specificities between nPCR62/64 (97%) and culture 63/64 (98%) (Chi2 p = 1.0). Cell content was important for viral detection by nPCR (Chi2 p = 0.07) but not culture. Nesting was found necessary for sensitivity and did not reduce specificity. Assay under-performance appeared related to sub-optimal cell content (20%) but may have reflected clinical over-diagnosis. The results suggest the need for validating specimen cell quality. CONCLUSIONS This study questions the value of routine laboratory confirmation of mucosal herpetic infection. The adoption of a more discriminatory usage of laboratory diagnostic facilities for genital herpetic infection, taking account of cell content, and restricting it to those cases where it actually affects patient management, may be warranted.