Repeat Molecular Testing for Respiratory Pathogens: Diagnostic Gain or Diminishing Returns?

Background: Upper respiratory tract infections are common, and the ability to accurately and rapidly diagnose the causative pathogen has important implications for patient management. Methods: We evaluated the test-ordering practices for 2 commonly utilized nucleic acid amplification tests (NAATs) for the detection of respiratory pathogens: the Xpert Flu Assay for influenza A/B (Flu assay) and the Biofire FilmArray respiratory panel assay (RP assay), which detects 20 different targets. Our study examined repeat testing; that is, testing within 7 days from an initial test. Results: Our study found that repeat testing is common for each of the individual assays: 3.0% of all Flu assays and 10.0% of all RP assays were repeat testing. Of repeat testing, 8/293 (2.7%) of repeat Flu assays and 75/1257 (6.0%) of RP assays resulted diagnostic gains, i.e., new detections. However, for the RP assay, these new detections were not always clinically actionable. The most frequently discrepant organisms were rhinovirus/enterovirus (28/102, 27.5%), followed by respiratory syncytial virus (12/102, 11.8%) and coronavirus OC43 (11/102, 10.8%). Furthermore, there were 3,336 instances in which a patient was tested using both a Flu assay and RP assay, of which only 44 (1.3%) had discrepant influenza results. Conclusions: Our findings suggest opportunities exist to better guide ordering practices for respiratory pathogen testing, including limiting repeat testing, with the goal of optimization of clinical yield, and diagnostic stewardship.