BackgroundChlamydia pneumoniae causes of respiratory diseases and could also present as a secondary complications in respiratory diseases with very serious sequelae. This study screen Chlamydia pneumoniae in hospitalized individuals with previously known respiratory diseases.DesignThe six geopolitical zones of Nigeria were sampled with stop stations at each of the zones. Males and females were stratified according to age groups since age is a possible cofounder that may immediately affect the results. Individuals with previous respiratory diseases and hospitalized served as cases while those with respiratory diseases and not hospitalized served as control 1and those without respiratory diseases were control 3. MethodsBlood samples were tested using the microimmunoflourescence assay using antigen from specimens cultured into chickenâ€™s embryonated eggs. Staitistical evaluation was done using both Microsoft excel and SPSS version 13.ResultsOf the 2652 patients screened for Chlamydia pneumoniae IgG and IgM, using the microimmunoflourescence test, 2612 (98%) were positive. Patients with bronchitis had the highest positive result (60%) while pneumonia patients had the lowest (51%). The IgM and IgG distribution in the patients were also high. Antibody titeration among hospitalized patients was also high when compared to the two controls. Attack rate was highest in patients with sinusitis and bronchitis been lowest. Age group distribution in all the patients shows that the extreme ages had the highest distribution of antibodies especially of the IgM class. Chlamydia pneumoniae infection was sexually distributed in patients with bronchitis, asthma and sinusitis.ConclusionsIn conclusion Chlamydia pneumoniae was responsible for the secondary complication (exacerbation) in hospitalized patients with age and sex as cofounders. Chlamydia pneumoniae was age and sexually distributed and this depended on the type of respiratory disease.