[Bronchiolitis caused by influenza type A virus. An emerging infectious disease].

Objectives: To prospectively study the emergence and diagnostic problems of bronchiolitis caused by influenza A virus among children durign the 1999-2000 influenza epidemic.

Materials And Methods: Negative respiratory syncitial virus (RSV) specimens (ELISA dot-blot) were seeded in the MDCK cell line for the isolation of influenza A virus, by the shell-vial technique. Vials were revealed by indirect immunofluorescence with antibodies directed against the influenza A virus nucleoprotein (Monofluookit IA, Pasteur Diagnostics). The clinical and epidemiologic features of patients with viral recovery were studied. A theoretical cost/benefit study was performed on the usefulness of the rapid antigenic detection of the influenza A virus.

Results: A total of 117 cases of respiratory infection caused by influenza A virus were detected. In 62 cases (52.9%) the diagnosis was bronchiolitis. Of them, 80.6% of cases were aged less than 6 years. Subtype H3N2 predominated in all respiratory infections, paticularly in bronchiolitis. During the 1999-2000 season, a significant emergence of bronchiolitis caused by influenza A virus was observed (week 3, 30% cases of influenza A versus 24% of RSV). The cost/benefit study disclosed that the antigenic detection of RSV and influenza A virus in all respiratory specimens would amount up to 30.83 Euros/specimen.

Conclusions: During the last influenza epidemic, an emergence of bronchiolitis caused by influenza A virus among children was observed and confirmed. Based upon this observation, a dual strategy should be followed. On the one hand, a prophylactic approach (immunization of pregnant women); on the other hand, a diagnostic approach with a rapid antigenic detection of the influenza A virus.