Respiratory syncytial virus neutralizing activity in nasopharyngeal secretions.

Nasopharyngeal secretions were taken during the acute phase of illness from 30 children admitted to hospital with lower respiratory tract infections. The presence of neutralizing activity in secretions taken at the onset of illness was demonstrated in 11 out of 15 patients (73%) with bronchiolitis caused by R.S. virus, as compared with 4 out of 9 patients (44%) with R.S. virus infections other than bronchiolitis, and 1 out of 6 without R.S. virus infection. Second secretions were taken 7 days later from 10 of the children with R.S. virus infection. Eight of these paired secretions showed an increase of neutralizing activity against R.S. virus. It is suggested that the neutralizing activity, found in secretions taken at the onset of illness, may be a result of previous infection with R.S. virus.