Severity of respiratory syncytial virus disease related to type and genotype of virus and to cytokine values in nasopharyngeal secretions

Background Investigations concerning the severity of respiratory syncytial virus (RSV) disease as related to (1) RSV type and genotype determined resp ectively by PCR and restriction enzyme analysis and (2) interleukin 6 (IL-6 ) and turner necrosis factor alpha (TNF-alpha) values in samples of nasopha ryngeal secretion (NPS) have not been previously reported. Methods. We prospectively studied 105 RSV infections in the lower respirato ry tract of infants and young children admitted to a pediatric department i n Copenhagen during three winter seasons, 1993, 1994 and 1995, RSV strains were typed and genotyped, respectively, by PCR and nucleic acid restriction analysis and correlated to the severity of the disease. The ratio IL-6:TNF-alpha, determined from IL-6- and TNF-alpha values in sam ples of NPS, was related to the severity of the disease. Concentrations of IL-6 and of TNF-alpha were determined in serum samples taken during 5 weeks after the onset of illness. Results. Type B infections produced more severe disease than did type A inf ections, as assessed on the length of the hospital stay, use of respiratory support and the presence of an infiltrate on a chest radiograph, This diff erence was age-related. It was observed in infants 0 to 5 months old, but n ot in older age groups. Type B genotype B1122 produced more severe disease than type A genotype A2311 in infants 0 to 11 months old. Increased serum concentrations of IL-6 and TNF-alpha were detected in sampl es taken 1 to 2 days after the onset of illness. Whereas TNF-alpha serum co ncentrations remained high, IL-6 serum concentrations decreased during the following 3 to 4 weeks. The IL-6:TNF-alpha ratio in samples of NPS was related to the severity of t he disease. A high ratio was related to a low severity. Conclusions. The severity of disease in patients admitted with acute RSV in fections can be correlated to the RSV type as determined by PCR, to the RSV genotype as determined by nucleic acid restriction analysis and to the rat io IL-6:TNF-alpha in NPS.