Hospitalization cost estimates of respiratory syncytial virus and influenza infections in adults in Spain, 2016-2019.

Respiratory syncytial virus (RSV) is increasingly a recognized cause of severe respiratory infection among adults. This retrospective observational study compared the costs of RSV and influenza hospitalizations in adults aged ≥18 years admitted to the Spanish National Healthcare System between 2016 and 2019. Mean costs per hospitalization episode were compared using a multivariable log-gamma generalized linear model adjusted by age, risk group and calendar year. Total annual hospitalization costs were estimated from population incidence rates (for RSV we used model-based rates reported in a published study due to the substantial under-ascertainment of cases) and the mean cost per episode. ICD-10 codes identified a total of 11,662 adults hospitalized with RSV and 79,319 with influenza. The mean length of stay was longer for RSV than for influenza in low-risk patients aged 60-79 years, moderate-risk patients (those with chronic medical conditions) aged ≥50 years and in high-risk (those with immunocompromising conditions) patients aged <80 years. There were no differences in intensive care unit (ICU) admission (except for higher admission in high-risk RSV patients aged 70-79 years), ICU stay or in-hospital case fatality rate. Mean costs per hospitalization episode were also similar: RSV €3870 (95 % CI 3773-3942) vs influenza €3888 (95 % CI 3836-3931). Total annual costs for RSV-attributable hospitalizations were estimated at M€194, twice than that of influenza (M€83). Annual costs increased by 11 % over the study period for RSV and by 47 % for influenza. In 2019, adults aged ≥60 years and ≥ 70 years contributed 91 % and 82 %, respectively, of the total RSV-attributable hospitalization costs in adults. RSV has a significant economic burden to the Spanish National Healthcare System, likely greater than influenza. Efficacious RSV vaccines and antivirals have the potential for high public health impact.