Denominator and Workflow Dependence of Age-Specific Viral Detection in Cerebrospinal Fluid

Longitudinal cerebrospinal fluid PCR archives may show apparent age patterns shaped jointly by underlying disease processes and testing architecture. We examined how apparent viral detection patterns varied with denominator choice, target availability, and reconstructed testing configurations among patients tested at a Korean tertiary-care hospital from 2006 to 2026. Clinical diagnoses and adjudication were unavailable, and workflows were reconstructed from reporting configurations rather than definitive platform identifiers. The archive contained 30,481 target-level results from 5353 patient-date episodes in 4560 patients. We summarized per-target positivity, viral-positive composition, and contextual pooled target-level positivity. Human herpesvirus-6 target-level positivity peaked at 31.9% (272/854) at age 1–4 years and comprised 75.8% (91/120) of infant and 84.0% (272/324) of 1–4-year viral-positive detections. However, HHV-6 was represented in 79.9% and 96.1% of episodes in these groups, whereas enterovirus was represented in only 14.4% and 3.9%. VZV was the most frequently detected adult viral target in the full archive, although rankings varied by period. Apparent age patterns were therefore conditioned by target availability, denominator choice, and evolving workflows and should not be interpreted as clinically adjudicated CNS infection epidemiology.