(A-347) Patient and Epidemiological Factors Associated with Respiratory Syncytial Virus (RSV) Testing in Adults Hospitalized with RSV-Like Illness, 2023–2024 Respiratory Season

Background: Real-world vaccine effectiveness (VE) evaluations using test-negative designs require testing among symptomatic persons presenting for medical care. Understanding factors associated with respiratory syncytial virus (RSV) testing will assist with interpretation of results from RSV VE studies that use test-negative designs.

Objectives: To assess patient-level, facility-level, and calendar time factors associated with clinician-ordered RSV testing in patients admitted to a hospital with an RSV-like illness (RLI).

Methods: We included adults aged ≥50 years with a diagnosis code consistent with RLI during a hospitalization from October 1, 2023, to March 31, 2024 at participating VISION partner sites in the US. The outcome was any RSV testing between 10 days prior to 72 hours following hospitalization. Variables included in the factor analysis were site, tertiary or community hospital, urban or rural facility, encounter month, age, sex, race and ethnicity, Medicaid status, body mass index, Social Vulnerability Index (SVI), any underlying medical conditions, immunocompromising conditions including HIV infection, and history of RSV vaccination. Factors were selected using a random forest model based on permutation variable importance measures. Adjusted odds ratios (aORs) with 95% confidence intervals (CIs) for RSV testing were estimated using a multivariable logistic regression model.

Results: Among 73,684 hospitalizations with an RLI diagnosis during the study period, 29,250 (39.7%) had RSV testing. The odds of RSV testing were higher in patients who were aged ≥75 years (aOR: 1.18, 95% CI: 1.13–1.24) vs. 50–59 years, who were female (aOR: 1.07, 95% CI: 1.04–1.11), Hispanic (aOR: 1.14, 95% CI: 1.06–1.22) vs. Non-Hispanic White, hospitalized in large metro areas (aOR: 1.13, 95% CI: 1.09–1.18), admitted in January (aOR: 1.84, 95% CI: 1.74–1.94) vs. October, and insured by Medicaid (aOR: 1.07, 95% CI: 1.02–1.12). Patients residing in the most vulnerable neighborhoods, SVI quartile 4 (aOR: 0.91, 95% CI: 0.85–0.97) vs. SVI quartile 1, those admitted to tertiary hospitals (aOR: 0.87, 95% CI: 0.83–0.91), and those with underlying medical conditions (aOR: 0.70, 95% CI: 0.66–0.74) had lower odds of having an RSV test.

Conclusions: Multiple factors influenced RSV testing among adults ≥50 years admitted with an RLI. This work will help quantify selection bias and inform interpretation of RSV VE estimates.