Incidence of respiratory syncytial virus-associated hospitalization among adults in Ontario, Canada, 2017-2019

Background — Respiratory syncytial virus (RSV) causes substantial morbidity and mortality among adults. Given recent RSV vaccine authorizations, data on groups at highest risk are needed to support vaccine program decision making.

Methods — We identified adults aged ≥ 18 years hospitalized with laboratory-confirmed RSV and hospitalizations with RSV-related diagnostic codes in Ontario, Canada (2017–2019). We calculated incidence of hospitalization with 95% confidence intervals (CIs) using Poisson regression stratified by demographic and clinical risk factors, and substratified by age. We reported secondary outcomes including the proportion of individuals with fatal outcomes.

Results — Over 2 respiratory virus seasons, we identified 3928 RSV-associated hospitalizations. Incidence increased steadily with age from 2.0 (95% CI, 1.8–2.3) per 100 000 for those aged 18–49 years to 43.7 (95% CI, 41.0–46.6) per 100 000 for those aged 70–79 years, with a sharp increase to 134.7 (95% CI, 128.6–141.1) per 100 000 for those aged ≥ 80 years. Incidence was higher for those with comorbidities, including chronic kidney disease (receiving dialysis) (494.7; 95% CI, 410.7–595.8) and transplant recipients (370.9; 95% CI, 318.0–432.6), as well as for those living in lower (22.4; 95% CI, 21.1–23.7) versus higher-income neighborhoods (11.8; 95% CI, 10.8–12.8). Among those hospitalized, 10.3% (n = 403) died within 30 days of admission, and 93.1% of deaths occurred in those aged ≥ 60 years. Of survivors, 44.6% of community-dwelling adults aged ≥ 60 years had functional decline requiring formal supports at discharge.

Discussion — We found a substantial burden of RSV among older adults, particularly among those with preexisting medical conditions and those of lower socioeconomic status. These results will inform equitable vaccine recommendations for adults.