Broad multiplex respiratory panel implementation and antibiotic prescribing in US emergency and urgent care...

To evaluate the association between department-level implementation of broad multiplex respiratory pathogen panels and antibacterial prescribing.

Retrospective repeated cross-sectional staggered-adoption study with cohort-stacked difference-in-differences models.

US emergency and urgent-care departments contributing deidentified electronic health record data to Epic Cosmos, 2016-2025.

Adults with acute respiratory illness without a concurrent clear nonrespiratory bacterial indication.

Incident implementation was the first sustained increase in strict panel use from below 2% to at least 10%, with complete 8-quarter preimplementation and postimplementation windows. Adopters were compared with contemporaneous nonadopters and not-yet-adopters. The primary outcome was a same-day systemic oral or enteral antibacterial order after emergency department discharge.

Among 55,059,432 eligible encounters, 32 adopting departments in 9 cohorts were compared with 1,075 departments, yielding 114,832 department-quarter observations. Implementation was associated with a 23.53-percentage-point increase in panel use (95% CI, 20.32 to 26.74) and a 1.21-percentage-point reduction in same-day antibacterial prescribing (95% CI, -2.37 to -0.05; P = .041), a 5.7% relative decrease. However, alternative 5, 15, and 20% thresholds were not statistically significant, unrestricted analyses were null, and several preimplementation diagnostics rejected flat trends.

Sustained panel implementation was associated with a small reduction in antibiotic prescribing. Threshold sensitivity and mixed preimplementation diagnostics limit causal interpretation and support integrating testing into broader diagnostic-stewardship workflows.