ObjectiveExploring the influencing factors of acute phase (≤ 21 days) seizures and epilepsy in patients with Herpes simplex virus encephalitis (HSE) in our hospital, including emergency and inpatient wards, mainly from the perspective of the number of mNGS of Herpes simplex virus (HSV) in cerebrospinal fluid. MethodsFrom January to Octomber 2023, 28 emergency and inpatient patients in our hospital were collected, excepted clinical datas were not detailed. In the end, 24 patients with HSE diagnosed were included in the study, and their clinical datas were collected, including age, gender, acute encephalitis syndrome, the form of the seizure and the number of seizures, time of lumbar puncture, and various indicators of cerebrospinal fluid [pressure, protein, cell count (mononuclear and multinucleated cells), metagenomic Next-generation sequencing (mNGS), neural autoantibodied associated with autoimmune encephalitis], electroencephalogram, cranial imaging examination reports, and treatment plans.ResultsA total of 24 patients were enrolled, including 9 patients with a history of hypertension and 4 patients with a history of diabetes. There were 18 males and 6 females, with an average age of (53.17±17.19) years. The maximum age was 73 years old, and the minimum age was 21 years old. Among the 24 patients, one patient first presented to the local hospital and then transferred to our hospital for lumbar puncture, so the time from the onset of the disease to lumbar puncture was 30 days, and the other patient’s family members refused to complete lumbar puncture at first,so the time of lumbar puncture was 14 days from the onset of the disease. The remaining 22 patients were all completed lumbar puncture within 7 days of onset, and all emergency patients completed lumbar puncture within 24 hours of admission to the Emergency Department. mNGS results: 23 cases were HSV-1, and the remaining 1 case was HSV- 2. There were a total of 6 cases of seizures and epilepy in the acute phase (≤21 days), with focal or generalized seizures or epileptic status as the main form, and 2 cases of seizures occurred. Among these 8 patients, 5 showed lesions in the frontal and temporal lobes on enhanced cranial MRI, while the other 3 showed no specific features. At the same time, mNGS of cerebrospinal fluid suggested that the sequence number of HSV was greater than 3 000 was related with seizures and epilepsy with acute HSE. Conclusion Seizures and epileysy in acute HSE were related with the presences of intracranial cortical involvement,and the number of viral sequences in mNGS was closely related to acute phase seizures and epilepsy.