Variations in the pathophysiology of respiratory syncytial virus infection depend on the age at onset.

Background: Lower respiratory tract infections due to respiratory syncytial virus are associated with morbidity and mortality in infants and children. Thus precise elucidation of respiratory syncytial virus lower respiratory tract infection pathophysiology is important.

Methods: Medical records of hospitalized patients were reviewed. Patients were divided into three groups. Group I: patients who improved without oxygen supply. Group II: patients who received oxygen supply, but not nasal high-flow cannula therapy. Group III: patients who received nasal high-flow cannula. Patients were also divided by age group into the <6 months and ≥6 months groups. Parameters for differentiating the severity among groups were then evaluated. Further, serum concentration of high-mobility group box-1 and several cytokines (Inerleukin-6, soluble tumor necrosis factor receptor-1/2, Interleukin-18, Interferon-gamma responsive protein-100) were evaluated.

Results: One hundred eighty-nine were enrolled. An analysis of variance for those <6 months showed overall differences including younger age, lower pH, and increased partial pressure of carbon dioxide (pCO2), bicarbonate (HCO3-), and base excess at the time of admission. On the other hand, analysis of variance for ≥6 months revealed that, in addition to a lower pH and increased pCO2, patients showed differences including decreased serum total protein and albumin, and increased aspartate aminotransferase (AST), alanin aminotransferase (ALT), lactate dehydrogenase (LDH), Ferritin and C-reactive protein (CRP) levels. Further, evaluation of serum cytokines showed that IL-6, s tumor necrotizing factor receptor-1/2, and high-mobility group box-1 were higher in Group II/III among the ≥6 months age group, but not for those in the <6 months group.

Conclusions: The pathophysiology of severe respiratory syncytial virus lower respiratory tract infection varies according to the age at onset. In late infancy and childhood, a certain proportion of patients show a hyperinflammatory status.