[Viral infection related to the appearance of acute bacterial respiratory tract infections].

To investigate what viruses are related to acute bacterial respiratory tract infections, we prospectively evaluated 113 cases with respiratory tract infections (always accompanying by purulent sputum) experienced between July 1998 and March 2000. Acute viral infections were detected in 25 cases (22%); 10 cases of influenza A virus and 6 cases of respiratory syncytial (RS) virus. The epidemiology of the influenza A virus and RS virus was mainly identified as from December to February in both winter seasons. A bacteriological examination of sputum cultures isolated 12 cases of Streptococcus pneumoniae and 10 cases of Haemophilus influenzae during the same periods and mixed infections of both viruses and bacteria were recognised in 16 cases (14%). These results suggest a significantly high percentage of mixed infections of both viruses and bacteria. However, it was unknown whether the patients with acute bacterial respiratory infections had been infected with viruses prior to the bacterial infections. The frequency of appearance of respiratory tract infections tended to increase with the seasonale epidemiology of viral infections.