Abstract
BACKGROUND: Respiratory syncytial virus (RSV) incidence among adults in Finland remains underreported, mostly due to non-specific RSV symptoms, infrequent standard-of-care testing, and reduced sensitivity of single-specimen nasal/nasopharyngeal RT-PCR testing among adults. We retrospectively estimated RSV-attributable incidence of all-cause respiratory hospitalizations and mortality in adults in Finland between 2011 and 2019. METHODS: We estimated incidence using time-series modeling by comparing the week-to-week variability in RSV diagnosis trends with the week-to-week variability in the events with any respiratory diagnosis. Weekly aggregated data on all-cause respiratory hospitalizations and deaths (J00-J99) were obtained from the Care Register for Health Care (HILMO) and Statistics Finland, respectively. Hospitalization data on RSV and influenza were obtained from HILMO. Data on all-cause respiratory diseases for age groups that showed a seasonal pattern were included in a hierarchical Bayesian model, sharing information across the age groups while accounting for seasonal fluctuations, and RSV and influenza circulation. RESULTS: The highest annual incidence rates of RSV-attributable respiratory hospitalizations were observed in adults aged ≥ 75 years (range 145-240 hospitalizations per 100,000 person-years), on average 7-fold higher than in adults aged 45-64 years (range 19-37 hospitalizations per 100,000 person-years). A biennial (low-high incidence) fluctuation of all-cause respiratory hospitalization incidence and mortality rate was observed in all age groups. A seasonal pattern for all-cause respiratory deaths was observed only for adults aged ≥ 75 years, who had an estimated RSV-attributable mortality rate of 8-14 deaths per 100,000 person-years. RSV-attributable deaths accounted for 3-5% of all all-cause respiratory deaths in this age group. CONCLUSIONS: Respiratory morbidity and mortality associated with RSV infection among adults in Finland are substantial, particularly for those aged ≥ 75 years. Newly introduced RSV vaccines, which appear effective for the oldest adults, could have a substantial impact on this respiratory disease burden.