Viral loads of herpes simplex virus in clinical samples--a 5-year retrospective analysis

Viral loads of herpes simplex virus (HSV) are not monitored usually for the effective clinical management of HSV-related diseases. However, recently, there has been more interest about the typical HSV levels in clinical specimens, and how such data may improve understanding of the behavior of this virus in such clinical presentations, particularly in immunocompromised patients, where more prolonged therapy using higher doses of antiviral drugs may be required. Using an in-house quantitative HSV-1/HSV-2 polymerase chain reaction assay, an observational, retrospective 5-year analysis of diagnostic, quantitative HSV-1 and HSV-2 DNA levels was conducted. The results (all in median log(10) DNA copies/ml), including perhaps the first quantitative comparison of cerebrospinal fluid (CSF) HSV viral loads, were as follows: CSF: HSV-1, 3.40 (range 2.30-8.98) versus HSV-2, 3.60 (range 2.31-6.86) (P=0.559); plasma: HSV-1, 3.20 (range 2.23-5.51) versus HSV-2, 3.20 (range 3.18-3.41) (P=0.905); genital swabs: HSV-1, 6.79 (range 2.28-8.48) versus HSV-2, 6.97 (range 3.40-9.66) (P=0.810); oral swabs: HSV-1, 7.28 (range 2.46-10.04) versus HSV-2, 5.62 (range 4.60-6.63) (P=0.529). Note that with the samples usually collected for HSV testing (i.e., CSF, plasma, oral, and genital swabs) there was no significant difference in the viral loads between HSV-1 and HSV-2 types, nor between immunocompetent and immunocompromised patients for each of these different HSV types. Indeed, even between immunocompromised patients with similar diseases, for these samples, the HSV loads were found to vary considerably. These findings may therefore limit the usefulness of monitoring HSV loads in everyday clinical practice.