Etiologic and clinical evaluation of acute lower respiratory tract infections in young Argentinian children: an overview. This paper summarizes the first study on clinical, etiologic, and epidemiologic features of acute lower respiratory tract infection (ALRI) in children in Argentina. A total of 1,003 children less than 5 years of age (805 inpatients and 198 outpatients) presenting with ALRI were studied during a 40-month period. Nasopharyngeal aspirate (NPA), blood, urine, and throat-swab samples were collected when each child was first seen for care. Virologic studies were performed on the NPA by means of indirect immunofluorescence and isolation of virus in cell culture. Bacteriologic studies primarily were done by means of culture of blood or pleural fluid (when available); Bordetella pertussis and Mycoplasma pneumoniae, however, were searched for by the use of immunofluorescence and complement-fixation testing, respectively, in paired sera. Respiratory syncytial virus was the most commonly isolated virus, followed by adenovirus, parainfluenza virus, and influenza virus. Streptococcus pneumoniae was the most frequently isolated bacterium, followed by B. pertussis and Haemophilus influenzae type b. Overall, the patient fatality rate was 3.8% among inpatients with pneumonia or bronchiolitis. 