Pathogen-Specific Temporal Coupling Between Outpatient Influenza-like Illness and Hospitalized Severe Acute Respiratory Infection Positivity in China: A National Sentinel Surveillance Time-Series Study

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Outpatient influenza-like illness (ILI) and hospitalized severe acute respiratory infection (SARI) surveillance measure respiratory-pathogen activity in distinct clinical settings. We analyzed 95 epidemiological weeks (2024-W46 to 2026-W36) of national China CDC positivity data for ten respiratory viruses and Mycoplasma pneumoniae. For each pathogen, weekly change in SARI positivity was regressed on ILI changes at lags 1–4, with adjustment for four SARI autoregressive lags and annual seasonality. Inference used Newey–West covariance, joint lag tests, and Benjamini–Hochberg false-discovery-rate correction; reverse-direction, specification, recursive block-bootstrap, prewhitened cross-correlation, rolling-coefficient, and rolling-origin forecast analyses were secondary. Asymptotic forward lag blocks were FDR-significant for ten pathogens, whereas recursive block-bootstrap inference supported six: influenza virus, respiratory syncytial virus, human metapneumovirus, parainfluenza virus, common human coronavirus, and rhinovirus. No augmented model showed FDR-significant evidence of improved forecast error at 1-, 2-, or 4-week horizons; with only 35–38 forecast origins, modest incremental value could not be excluded. National ILI and SARI positivity series showed pathogen-specific temporal coupling, but this 95-week record did not establish fixed lead times or incremental prospective forecasting value in this dataset.