Burden of disease and cost of illness of infants less than 6 months of age hospitalised with respiratory syncytial virus in Denmark - a 10-year national register-based study.

Background: Respiratory syncytial virus (RSV) is the most common cause of hospitalisation in infants aged ≤ 6 months in Western countries. Nearly 1,500 infants under six months of age are hospitalised with RSV annually in Denmark. This nationwide study describes the healthcare resource utilisation and costs related to RSV hospitalisation in this vulnerable age group.

Methods: RSV cases were identified in the Danish National Patient Register. Infants were included if they at the age of 0-5 months had a (1) respiratory related hospital admission (duration > 12 h), (2) within 10 days of a positive RSV test, (3) between January 2013 and December 2022. Each case was matched with five individuals never diagnosed with RSV on age, sex, region of residence, birth (pre/full term), number of siblings < 7 years old, and parents' education. An episode of RSV was defined as the seven days prior to hospitalisation to 30 days after initial hospitalisation. Study outcomes included contacts with hospital and primary care, and total healthcare costs defined as the sum cost of hospital care, primary care, and prescription medicine. Cost and contacts attributable to RSV was calculated in a diff-in-diff framework, as the difference between case and reference group.

Results: The study population comprised of 8,428 RSV cases and 41,725 reference individuals. Cases generated 1.58 (p < 0.001) attributable inpatient contacts, 0.84 (p < 0.001) outpatient contacts, and 1.19 (p < 0.001) primary care contacts during their RSV episode. An additional 0.6 (p < 0.001) inpatient, 1.08 (p < 0.001) outpatient and 2.42 (p < 0.001) primary care contacts were attributed to RSV in the year following the RSV episode. Total cost of an RSV episode was EUR 2,997 (p < 0.001) with an additional EUR 1,428 (p < 0.001) in the following year.

Conclusion: RSV hospitalisations of infants are associated with substantial healthcare utilisation and costs. The same pattern was observed in the year following the RSV episode. If the new RSV prevention options are introduced nationwide, the overall burden of RSV is expected to be substantially reduced in the future.