Hospital SARS-CoV-2 surveillance across inpatient testing, fever clinic, and general outpatient settings: positivity, Ct gradients, and short-lag warning signals.

Background: Hospital-based SARS-CoV-2 surveillance needs to distinguish front-end detection settings from inpatient testing burden and evaluate whether outpatient virological signals can provide early warning for downstream hospital pressure. Methods: We conducted a single-center retrospective observational study using all SARS-CoV-2 nucleic acid test records from Zhengdong Campus, The First Affiliated Hospital of Zhengzhou University, between 20 December 2022 and 31 December 2025. The unit of analysis was individual test specimens, classified into fever clinic, general outpatient, and inpatient testing groups. Statistical analyses included chi-square tests, non-parametric tests, logistic regression, and time-lagged correlation analyses. Results: Among 24,751 tests, 5,000 were positive (overall positivity 20.2%). Positivity was highest in the fever clinic (26.9%), followed by general outpatient (23.5%) and inpatient settings (16.3%). Among 4,134 positive tests with available cycle threshold (Ct) values, median Ct was highest in inpatients (30.0) and lower in fever clinic (28.0) and general outpatient (27.0) settings. The proportion of general outpatient positives with Ct < 25 showed the strongest overall association with subsequent inpatient positivity at a lag of 2 biweekly intervals. Outpatient settings concentrated stronger virological signals, while inpatient testing carried the largest absolute burden of positive results. Conclusion: The general outpatient clinic functions as a meaningful front-end surveillance interface rather than a low-risk background category. Monitoring low-Ct enrichment in outpatient settings can provide a pragmatic early warning for short-term inpatient pressure, supporting broader outpatient-focused hospital infection prevention strategies.