Respiratory syncytial virus (RSV) is a common respiratory virus that can cause severe disease, particularly in older adults and adults with underlying medical conditions. However, RSV infections often go underdiagnosed due to infrequent testing and assay sensitivity limitations. To better understand RSV epidemiology and disease burden, we investigated respiratory virus testing patterns and characteristics associated with RSV testing among United States (US) adults aged ≥ 50 years with acute respiratory illnesses (ARIs). This was a retrospective study using Optum® electronic health records data from 2015 to 2023. Medically-attended ARIs were identified among adults aged ≥ 50 years; percentages of ARIs tested for RSV and other respiratory viruses were calculated and stratified by epidemiological year (EY) and most intensive care setting during the ARI episode. Patient, provider, and ARI characteristics associated with the likelihood of RSV testing were assessed using multivariable logistic regression models. Among 22,475,891 included ARIs, RSV testing occurred in 2.4% (n = 530,452) of episodes. RSV testing increased over time (1.3-5.9% from 2016-2017 to 2022-2023 EYs), though it remained markedly lower than influenza (5.8-15.1%; 2016-2017 to 2022-2023 EYs) and SARS-CoV-2 (5.8-22.6%; 2019-2020 to 2022-2023 EYs) testing. By most intensive level of care received, RSV testing from 2016-2023 was more frequent in inpatient (9.5-27.5%) and emergency department (ED; 1.4-17.9%) settings than the outpatient setting (0.3-1.4%). Among included covariates in adjusted analyses, most intensive care setting ED: 9.3-fold, inpatient: 31.2-fold (versus outpatient) and healthcare organization (0.02-13.8-fold) were most significantly associated with likelihood of RSV testing. The likelihood of RSV testing varied significantly by most intensive care setting and healthcare organization. Despite increasing RSV testing over time, RSV remains infrequently tested among US adults. Under-detection of medically-attended RSV cases should be accounted for when estimating RSV disease burden and the potential impact of RSV prevention strategies. A Graphical Abstract is available for this article.
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