Researchers at Seoul National University and other centers in Korea examined the clinical characteristics of enteroviral meningitis in 390 infants and children; 16-18% were without CSF pleocytosis. Enteroviral meningitis was diagnosed by nested RT-PCR assay in 277 cases and by GeneXpert assay in 113. CSF culture performed in 273 patients (70% of total) was positive in 104 cases (38% of those tested). Of the 390 with enteroviral meningitis, 71 (18%) did not have pleocytosis. The proportion without pleocytosis among neonates aged 0-27 days was 77%; in infants 28-55 days it was 44%; 56 days to 1 year, 30%; toddlers 2-4 years, 10%; and children 5-18 years, 6%. The proportion of patients without pleocytosis decreased significantly with age (p<0.001). Absence of CSF pleocytosis was associated with younger age, lower peripheral white blood cell count, and shorter interval between onset and lumbar puncture. 
COMMENT. CSF enterovirus PCR testing is recommended to evaluate suspected enteroviral meningitis, especially in young infants, even though pleocytosis is absent. The authors hypothesize that if the time from onset of meningitis to LP is short, the immunological response that recruits WBCs to CSF may not be complete, with absence of the expected pleocytosis.