Virological studies were done in a group of 112 infants under one year of age hospitalized with acute lower respiratory infections and in 41 healthy controls of the same age. Samples of nasopharyngeal aspirates were taken in both groups. Smears for immunofluorescencc of respiratory syncytial virus (RSV), parainfluenza type 3 virus, adenovirus and direct viral isolation technics were performed. Matched samples for serology were also done in 38 cases. Virological studies were positive in 72.3 percent of patients; in 82.7 percent of them RSV was demostrated while in 16.0 percent there were viral associations. The Virological studies in the control group were positive in 36.6 percent of cases for RSV and cytomegalovirus. This results confirms the role of RSV in the etiology of bronchopneumonia in infants under one year of age. (Key woids: respiratory tract infections, pneumonia viral, respiratory syncytial virus, para influenza type 3 virus, adeno viruses).

This study viral on participation in low acute respiratory tract infections (ARI) in 344 infants under 2 year of age was carried between years 1983 through 1985, by means of antigen detection and serological tests. A global positive isolation, was confirmed in 59.6% of cases (n = 205) with respiratory syncytial virus (RSV: n = 134; 65.4%), adenovirus (Ad: n = 41; 20.0%) and parainfluenza viruses (PI: n = 25; 12.7%) as the most commonly found agents. Mixed viral infections were detected in 16.6% of cases (n = 34). RSV showed the highest prevalence in all groups, mainly in patients under six months of age. PI increased with patient's age and similar but less noticeable raise ocurred in Ad infections. RSV was the only pathogen detected in infants with bronchial obstructive disease and was the prevalent organism in patients with all the other forms of disease. Ad and PI were equally found in all clinical syndrome without striking differences among each other. Influenza and citomegalovirus were also detected, but not clear evidence of pathogenic role was obtained for the later. Immunofluorescence was the best technique for RSV identification while isolation was better for Ad, The relevance of these viruses as causative agents of low ARI is confirmed and the need to further investigate other non viral etiologic agents is stressed.

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Studies on the etiology of lower respiratory infectionsAs a contribution to knowledge about the etiology of lower respiratory tract infections (LRI) in infants, 235 patients aged one year or less admitted to a children's hospital at northern metropolitan area of Santiago, Chile along years 1987 throughout 1989 with radiologically confirmed diagnosis were studied. Infants were eligible only if their symptoms lasted for not more than five days and their hospital stay was less than two days. Controls consisted on 74 healthy infants. A search for presumtive etiology was done by means of usual bacteriological procedures {pharyngeal swabs and blood cultures), plus latex test for type b Haemophitus influanzae (Hib) and Streptococcus pneumoniae (SP* in concentrated urine specimens; indirect inmunofluorescence (IF) for specific Chlamydia tracbomatis