RESULTS: 61.2% of our RSV patients had bronchiolitis, while the remainder had RSV pneumonia. The mean duration of oxygen support was 7.0 days ± 0.9 days, while the mean length of hospitalization was 9.8 ± 1.2 days. In this cohort of patients, 29%, 23% and 48% of RSV patients were admitted to the ICU, SCU and Respiratory Floor, respectively. High levels of active MMP-9 (endogenously present) were measured in the nasal secretions of hospitalized infants and children, during the first day of their hospital admission (regardless of unit). Total MMP-9 (includes pro-MMP-9) was similarly increased, and compared to the controls, higher MMP-9:TIMP-1 ratios were consistently measured in the nasal secretions. In contrast to the control subjects, higher levels of nasal IL-1, IL-4, IL-8 and IL-10 were measured in RSV patients. INFs (α/γ) were also increased, likely representing the host response to the RSV infection. Patients who had the longest duration of oxygen requirement had the highest levels of nasal MMP-9 activity. In the control non-RSV group, no correlation was observed between all the measured biomarkers and clinical markers of disease severity and outcome measures.