[Assay of specific anti-Chlamydia pneumoniae antibodies by ELISA method. 2. studies on clinical usefulness and serological diagnostic standards].

We measured anti-Chlamydia pneumoniae (C. pneumoniae) specific antibody titers by means of a newly-developed enzyme-linked immunosorbent assay (ELISA) method using an anti-C. pneumoniae specific antibody detection reagent. The clinical usefulness of this method was hereby evaluated. The IgG, IgA and IgM titers in 418 serum specimens obtained from patients with respiratory tract infections were measured by this new ELISA method, and the results were compared with the titers determined for the same specimens with the micro immunofluorescence (Micro-IF) method. The results showed good correlation coefficients for IgG, IgA and IgM. The two assay methods showed high agreement rates for positivity and for negativity. Specimens which did not yield the same results with the ELISA method and the Micro-IF method were subjected to analysis by the Western blot method, and the rates of agreement with the ELISA results were high. In addition, the child (0 approximately 15 yrs old; n = 122) and adult (16 approximately 90 yrs old; n = 133) cases were classified on the basis of being antigen-positive or antigen-negative at the initial examination, and their antibody-positive rates were determined. The adults showed no statistically significant differences in the antibody-positive rates for either IgG or IgA antibodies as a function of the pretreatment antigen status. However, the children showed statistically significant (p < 0.001) differences in the antibody-positive rates for both IgG and IgA antibodies as a function of the antigen status in the antigen-positive group compared with the rates in the antigen-negative group. Furthermore, the IgM-positive rates for the children were high in the antigen-positive group compared with the rates in the antigen-negative group, and the difference was statistically significant (p < 0.001). The IgM-positive rates in the adults were also significantly (p < 0.05) different between the antigen-positive group and the antigen-negative group. The Micro-IF method was applied to 34 specimens from antigen-positive patients, and 22 specimens were found to show an IgG titer of > or = 512 or an IgM titer of > or = 16. The diagnoses of these patients were acute respiratory disease in sixteen, pneumonia in four. Application of the ELISA-method to those 22 specimens showed all of them to exhibit IgG absorbance of > or = 0.6 and IgA absorbance of 0.2. The results described above indicate the clinical usefulness of our new ELISA method for the detection of antibodies specific for C. pneumoniae. The significance of this ELISA method for serological diagnosis of C. pneumoniae infections and the criteria for diagnosis of acute infections were also discussed.

[The etiology of acute lower respiratory tract infections in infants].

The etiology of acute lower respiratory tract infections (ALRI) was studied in pediatric inpatients under 2 years of age admitted to Chiba Municipal Hospital between June 1994 and March 1995. Eighty-seven patients, 99 episodes were investigated for bacterial infection with the use of blood culture and washed sputum culture, for viral infection with the use of virus isolation, antigen detection and antibody assays, for Mycoplasma pneumoniae infection with the use of antibody assay and for Chlamydia infection with the use of antigen detection. Pathogens were identified in 71 (71%) of the 99 episodes. Evidence of bacterial infection was detected in 43 episodes (43%), viral infection in 37 episodes (37%), Mycoplasma pneumoniae infection in 4 episodes (4%) and Chlamydia infection 3 episodes (3%). The major bacterial pathogens were H. influenzae, M. (B) catarrhalis and S. pneumoniae. RS virus and influenza virus epidemics occurred during the winter. A mixed bacterial and viral infection was documented in 13 episodes (13%). RS virus infection was common in infants up to 6 months old. Mixed bacterial and influenza virus infections were common in 1 or more year old children. Virus isolation was useful for the grasp of the viral epidemic. Bacterial associated infections were common in children under 2 years of age with ALRI. Washed sputum culture and sputum gram stains' were useful for the treatment of infant ALRI.