The incidence of Chlamydia psittaci antibodies in patients with respiratory tract diseases.

The incidence of Chlamydia psittaci infections in Hamburg has been studied using the complement fixation test on 655 human sera collected from patients with respiratory tract diseases. Of the 653 sera investigated, 78 (11.9%) showed antibody titers between 1:8 and 1:128. Of the positive sera, 21 (16.9%) presented values of greater than or equal to 1:32. This infection is encountered more often in individuals over 21 years of age (15.9% to 23.4%) than in persons under 20 (0.8% to 6.0%). General practitioners' attention must be drawn to Chlamydia psittaci infections, since they seem to be of greater importance in human pathology than is generally assumed.