Herpes simplex virus (HSV) infections of the central nervous system (CNS) are associated with significant morbidity and mortality rates in children. This study assessed the impact of a direct HSV (dHSV) PCR assay on the time to result reporting and the duration of acyclovir therapy for children with signs and symptoms of meningitis and encephalitis. A total of 363 patients with HSV PCR results from cerebrospinal fluid (CSF) samples were included in this retrospective analysis, divided into preimplementation and postimplementation groups. For the preimplementation group, CSF testing was performed using a laboratory-developed real-time PCR assay; for the postimplementation group, CSF samples were tested using a direct sampleto-answer assay. All CSF samples were negative for HSV. Over 60% of patients from both groups were prescribed acyclovir. The average HSV PCR test turnaround time for the postimplementation group was reduced by 14.5 h (23.6 h versus 9.1 h; P Ͻ 0.001). Furthermore, 79 patients (43.6%) in the postimplementation group had dHSV PCR results reported Ͻ4 h after specimen collection. The mean time from specimen collection to acyclovir discontinuation was 17.1 h shorter in the postimplementation group (31.1 h versus 14 h; P Ͻ 0.001). The median duration of acyclovir therapy was also significantly reduced in the postimplementation group (29.2 h versus 14.3 h; P ϭ 0.01). Our investigation suggests that implementation of rapid HSV PCR testing can decrease turnaround times and the duration of unnecessary acyclovir therapy.KEYWORDS HSV, acyclovir, encephalitis, herpes simplex virus, meningitis, rapid diagnosis, toxicity H erpes simplex viruses (HSVs) are important causes of meningitis and encephalitis, particularly among children and immunocompromised patients (1). The HSV infection rate among neonates is estimated to be 1 case per 32,000 deliveries, and approximately 1,500 cases of neonatal HSV disease occur annually in the United States (2, 3). Prompt initiation of antiviral therapy is paramount, as mortality rates for disseminated neonatal infections can be as high as 80% if the infections are left untreated; 70% of survivors are left with detrimental neurological sequelae (4-6).Patients with HSV meningitis and encephalitis typically have initial presentations of headache, fever, and altered mental status. However, neonates with HSV central nervous system (CNS) infections may have nonspecific presentations, including lethargy, irritability, poor oral intake, and temperature instability (7). Cutaneous vesicular lesions may be indicative of HSV infections in infants, but the absence of vesicular rash does not preclude neonatal HSV CNS infection in 35% of cases (8). Other infectious etiologies associated with CNS infections can present with similar symptoms (9). Thus, laboratory testing of cerebrospinal fluid (CSF) samples is necessary to confirm the diagnoses.