Role of Viral Load and Host Cytokines in Determining the Disease Severity of Respiratory Syncytial Virus-Associated Acute Lower Respiratory Tract Infections in Children.

Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infections (ALRTIs). In this study, we aimed to evaluate the role of viral load, cytokines, matrix metalloproteinase 9 (MMP-9), and tissue inhibitor of metalloproteinase 1 (TIMP-1) in determining the severity of RSV disease and identify potential biomarkers of disease severity. A total of 142 patients with RSV infection (aged between 2 months and 5 years) who presented with ALRTI between December 2013 and March 2016 were enrolled. Their nasopharyngeal aspirates were subjected to RSV viral load quantification, and local cytokine levels of interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), IL-17A, interferon γ (IFN-γ), and IL-10 were determined using a cytokine bead array. The levels of MMP-9 and TIMP-1 in 109 aspirates were calculated using Quantikine ELISA. These parameters were compared for different disease severity categories. A higher viral load and increased levels of TNF-α, MMP-9, and MMP-9:TIMP-1 were associated with greater severity of disease; whereas levels of IL-17A, IFN-γ, and IFN-γ:IL-10 were associated with disease resolution. When defining the transition from non-severe to severe disease, MMP-9 had a sensitivity and specificity of 89.7% and 85.4%, respectively. Moreover, MMP-9:TIMP-1 had a sensitivity and specificity of 87.2% and 76.8%, respectively. Hence, MMP-9, MMP-9:TIMP-1, TNF-α, and IL-10 could serve as potential biomarkers for disease progression in RSV-infected children.