Viral findings in children under the age of two years with expiratory difficulties.

Viral findings were prospectively studied in lower respiratory tract infections in small children with and without expiratory difficulties. On first admission, a viral aetiology was found in 71 of 127 children (56%). On re-admission, a viral etiology was found in only two of 31 cases (6%). Respiratory syncytial viruses (RSV) were responsible for 71% of the cases with viral diagnoses. A recently-developed method for the direct detection of viral antigens in nasopharyngeal specimens by radio-immunoassay was more sensitive than complement fixation serology, especially in patients aged less than six months. Viral diagnosis was reached using this new method alone in 43% of infections caused by RSV and in 27% of infections caused by other viruses. In children under six months, RSV were found in 89% by direct antigen detection and in 22% by serology. We suggest that direct antigen detection should be used as the primary virological method in small children with lower respiratory tract infections. The aetiological agents were the same in cases with and without expiratory difficulties, RSV being found in about 40% of children in both instances. It is concluded that host factors are critical to the development of expiratory difficulties.