Novel inflammatory markers, clinical risk factors and virus type associated with severe respiratory syncytial virus infection.

Background: Virus-induced inflammation contributes to respiratory syncytial virus (RSV) pathogenesis. We sought to determine the specific mediators that are associated with more severe illness in young children.

Methods: Children ≤ 5 years of age seen in our emergency department for respiratory symptoms from September 1998 to May 2008 were eligible for enrollment. Nasopharyngeal wash samples were collected from all eligible patients, and clinical data were recorded. Individuals were included in this study if nasopharyngeal wash samples were positive for RSV only. Patients enrolled in the study were stratified by disease severity, defined as mild (not hospitalized), moderate (hospitalized) or severe (requiring intensive care unit stay). Concentrations of individual inflammatory biomarkers in nasopharyngeal wash fluids were determined using the Luminex human 30-plex assay.

Results: Eight hundred fifty-one patients met study criteria: 268 (31.5%) with mild, 503 (59.1%) with moderate and 80 (9.4%) with severe illness. As expected, illness severity was directly associated with young age, prematurity, heart or lung disease, infection with RSV group A and elevated concentrations of interleukin (IL)-2R, IL-6, CXCL8, tumor necrosis factor-α, interferon-α, CCL3, CCL4 and CCL2. In addition, we report several novel and mechanistically important inflammatory biomarkers of severe RSV disease, including IL-1β, IL1-RA, IL-7, epidermal growth factor and hepatocyte growth factor.

Conclusions: In a large, longitudinal study (10 years, 851 enrolled patients) limited to RSV infection only, in which well-known risk factors are confirmed, we identified 5 novel biomarkers specifically of severe disease. These markers may ultimately serve to elucidate disease mechanisms.