Utility of Rt epidemic trend categories for influenza surveillance: alignment with observed emergency department trends across two influenza seasons in the United States

CDC has estimated the time-varying reproduction number (Rt) for influenza in the United States since 2023, translating the posterior probability that Rt exceeds one, P(R_t>1), into epidemic trend categories (growing, likely growing, not changing, likely declining, declining). If Rt reliably indicates infection dynamics, growing or declining trends should precede corresponding changes in influenza-related emergency department (ED) visits, accounting for the lag between infection and care-seeking. However, because these categories reflect confidence in the direction of change rather than magnitu

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