Chlamydia pneumoniae infection in children with lower respiratory tract infections.

The incidence of antibody and the clinical features of Chlamydia pneumoniae (C.pneumoniae) infection have not been studied in children in Japan. We investigated the incidence of C.pneumoniae antibody in sera from 580 healthy children (including 30 umbilical cord blood samples) during the 2-year period between June 1992 and June 1994. The antibody titer was determined by a microimmunofluorescence (MIF) test by using the elementary body of C.pneumoniae TW-183 as the antigen. Umbilical cord blood samples were positive for the antibody in 50% of newborns tested at birth. The incidence of positivity decreased to 0% in 1-year-old children. It was still low in children up to 5 years of age and then increased rapidly in children 6 years of age or older. The positivity reached increased rapidly in children 6 years of age or older. The positivity reached 55% in 7-year-old children and remained at this level in children older than 7 years of age. High antibody titer (IgG > or = 512), indicating recent infection, was observed in 13 (2.2%) of the 580 children, two of whom showed no symptoms. We detected the pathogen in throat swabs by culture and capillary polymerase chain reaction (PCR), and determined IgM and IgG serum titers to C.pneumoniae in 130 children with lower respiratory tract infection (91 with pneumonia and 39 with bronchitis) between December 1993 and December 1994. The infection due to C.pneumoniae was confirmed in 10 (7.7%). Of these, 7 were boys and 3 were girls, ranging in age from 9 months to 12 years. The clinical manifestations of the infection were mild symptoms like in common cold; post-nasal discharge, hoarseness and prolonged cough were relatively characteristic. There was no significant difference in the incidence of serum positivity between the healthy children group and the patients group. The present study suggests that primary-schoolers show antibodies for C.pneumoniae with nearly the same frequency as adults. Mild clinical symptoms are very common in C.pneumoniae infections in children as in adults.