[Epidemiological study on respiratory syncytial virus lower respiratory tract infections in northern Hokkaido, Japan].

We carried out an epidemiological study on lower respiratory tract infections, concerning the respiratory syncytial virus (RSV) infection, in northern Hokkaido, Japan, during the 2-year-study period from April 1991 to March 1993. There were 467 hospitalized patients with lower respiratory tract infections. We examined the presence of RSV antigen in their nasopharyngeal specimens of 456 out of 467 patients (97.6%) by enzyme immunoassay. The diagnosis of Mycoplasma pneumoniae infection was done by the rise of antibody titer, performed with complement fixation method, in the sera of the acute and convalescent phases. There were 133 patients with RSV infection (28.9%), 45 patients with Mycoplasma pneumoniae infection (9.8%) and 7 patients with measles virus infection (1.5%). RSV played an important role in the lower respiratory tract infections in northern Hokkaido, Japan. The epidemic of RSV infection was observed in spring and early winter in 1991 and only in early winter in 1992. The number of patients with RSV infection from April 1991 to March 1992 was greater than that from April 1992 to March 1993. In contrast with RSV infection, the epidemic of Mycoplasma pneumoniae infection was observed in 1992. We speculated that the RSV and Mycoplasma pneumoniae infections might interfere with each other.