To evaluate the utility of quantitative herpes simplex virus (HSV) polymerase chain reaction (PCR) levels for prognosis and management of neonatal HSV disease.

Clinical and virologic data were abstracted by medical record review from neonatal HSV cases treated at Seattle Children's Hospital between 1993 and 2012. HSV PCR results from plasma (n = 47), cerebrospinal fluid (n = 56), or both (n = 40) at the time of diagnosis were available from 63 infants; 26 with skin-eye-mouth (SEM), 18 with central nervous system (CNS), and 19 with disseminated (DIS) disease.

Plasma HSV PCR was positive in 78% of the infants with SEM, 64% with CNS and 100% with DIS disease. Mean plasma viral level was 2.8 log₁₀ copies/mL in SEM, 2.2 log₁₀ copies/mL in CNS, and 7.2 log₁₀ copies/mL in DIS infants. The HSV levels were higher among infants who died compared with surviving infants, 8.1 log₁₀ copies/mL (range 7.7-8.6) vs 3.8 log10 copies/mL (range 0.0-8.6), P = .001, however, level of HSV DNA in the cerebrospinal fluid or in plasma did not correlate with neurologic outcome. Dynamics of HSV clearance from plasma during high-dose acyclovir treatment showed single-phase exponential decay with a median viral half-life of 1.26 days (range: 0.8-1.51).

Plasma HSV levels correlate with clinical presentation of neonatal HSV disease and mortality, but not neurologic outcome.