Table 1_Temporal association between influenza A and B positivity and fever-clinic visit burden in Shanghai, China, 2022–2025: a retrospective time-series study.docx

Additional analyses excluded 2022, evaluated adjacent 0–21-day influenza A leads, and used Newey–West autocorrelation-robust inference.</p>Results<p>We included 254,346 fever-clinic visits and 303,597 outpatient influenza testing episodes. Overall influenza positivity was 33.96%, with 84,819 influenza A-positive and 18,504 influenza B-positive episodes. Influenza A was the main contributor to increased overall activity, particularly in 2023 and 2025.

Peak correlations occurred at −12 days for overall influenza positivity and −15 days for influenza A positivity, whereas influenza B peaked at the positive boundary of the primary window. In the extended analysis, the influenza B peak shifted to +50 days, indicating no stable leading relationship. High-burden days were preceded by higher overall influenza and influenza A positivity than reference days.

In the conventional testing-volume-adjusted model, influenza A positivity at a 15-day lead was associated with daily fever-clinic visits, but this association was attenuated after exclusion of 2022 and was no longer statistically significant with Newey–West inference. Adjacent-lag analyses did not identify a robust positive day-specific association after false discovery rate correction.</p>Conclusion<p>Outpatient influenza A positivity showed clearer temporal alignment with subsequent fever-clinic burden than influenza B. Although the fixed 15-day estimate was sensitive to period restriction and residual serial correlation, influenza A positivity may still serve as a complementary hospital-level surveillance indicator rather than a stand-alone forecasting tool.</p>