Epidemiology of RSV in Adults and Children with Medically-Attended Acute Respiratory Illness over Three Seasons.

BACKGROUND:Data on the true prevalence of RSV among medically-attended acute respiratory illnesses (MAARI) has been limited by the lack of regular clinical testing of mild to moderate illnesses. Here we present a prospective evaluation of the epidemiology of RSV-associated MAARI across age groups and multimorbidity status over three seasons, which is informative in light of the recommendations for shared decision-making for vaccination in older adults. METHODS:Ambulatory patients ≥6 months of age meeting a common MAARI case definition were prospectively enrolled in the Michigan Ford Influenza Vaccine Effectiveness (MFIVE) study, a subsite of the US Influenza Vaccine Effectiveness Network. All participants were tested by nasal-throat swab for RSV and influenza, including subtype, independently from clinician-directed testing. Participant illness characteristics and calculated Multimorbidity-Weighted Index (MWI) were collected by in-person survey and electronic medical record review. RESULTS:Over three surveillance seasons (fall 2017 to spring 2020), 9.9% (n=441) of 4,442 participants had RSV detected. RSV-associated MAARI was more prevalent than influenza for participants 6 months-4 years of age. Adults with RSV-MAARI had higher median MWI scores overall compared to influenza-MAARI and controls with neither virus (1.62, 0.40, and 0.64, respectively). CONCLUSIONS:RSV is a significant, underrecognized cause of MAARI in both children and adults presenting for ambulatory care. Multimorbidity is an important contributor to RSV-associated MAARI in outpatient adults, providing information to support shared clinical decision-making for vaccination.