Acute lower respiratory infections in hospitalized children over a 6 year period in Tokyo

Abstract

Background: Acute lower respiratory infections are major causes of hospitalization in children and are mainly caused by respiratory viruses. In the present study, we investigated the etiologic agents responsible for acute lower respiratory infections from the period November 1986 to October 1992 in order to determine the seasonal pattern and different characteristics of age distribution of respiratory infectious agents, mainly virus infections. Methods: A total of 1521 patients with lower respiratory infections was hospitalized in Saiseikai Central Hospital, Tokyo, Japan. Nasopharyngeal secretions were obtained for virus isolation and paired sera in the acute and convalescent phases were obtained for serological examination. Results: Etiological agents were identified in 668 of 1521 patients (43.9%) by serological antibody responses, virus isolation and/or detection of virus antigen: 240 (15.8%) with respiratory syncytial (RS) virus; 62 (4.1%) with influenza virus type A; 26 (1.7%) with influenza virus type B; 86 (5.7%) with adenovirus; 81 (5.3%) with parainfluenza virus; 32 (2.1%) with measles virus; 20 (1.3%) with enteroviruses or Herpes virus other than respiratory viruses; 75 (4.9%) with Mycoplasma pneumoniae; 10 (0.7%) with pertussis; and 36 (2.4%) with mixed infections. In the remaining 853 patients (56.1%), etiologic agents were not identified. Respiratory syncytial (RS) virus was a main causative agent of respiratory infections in patients younger than 3 years of age. Influenza virus and M. pneumoniae were two main causative agents in patients with acute respiratory illness over 5 years of age. Parainfluenza virus type 3 was frequently observed in infants from 9 to 12 months of age. A distinct seasonal pattern of viral infections was consistently observed in each year during the study period; RS and influenza viruses were prevalent in winter, parainfluenza virus was prevalent in spring and M. pneumoniae was prevalent in summer and autumn. However, adenovirus infections were observed in all seasons. Serological responses were poor in patients younger than 1 year of age and they were mainly diagnosed by virus isolation or detection of virus antigen. Conclusions: Virological epidemiology provides useful information in daily clinical practice for the prediction of etiological agents based on patient age and the seasonal distribution of agents. We should examine virus isolation and the detection of virus antigen, along with serological examinations in patients with respiratory infections, especially in infants younger than 1 year of age because of poor serological responses.