Chlamydia psittaci (psittacosis) as a cause of community-acquired pneumonia: a systematic review and meta-analysis

Abstract

Psittacosis is a zoonotic infectious disease caused by the transmission of the bacterium Chlamydia psittaci from birds to humans. Infections in humans mainly present as community-acquired pneumonia (CAP). However, most cases of CAP are treated without diagnostic testing, and the importance of C. psittaci infection as a cause of CAP is therefore unclear. In this meta-analysis of published CAP-aetiological studies, we estimate the proportion of CAP caused by C. psittaci infection. The databases MEDLINE and Embase were systematically searched for relevant studies published from 1986 onwards. Only studies that consisted of 100 patients or more were included. In total, 57 studies were selected for the meta-analysis. C. psittaci was the causative pathogen in 1·03% (95% CI 0·79-1·30) of all CAP cases from the included studies combined, with a range between studies from 0 to 6·7%. For burden of disease estimates, it is a reasonable assumption that 1% of incident cases of CAP are caused by psittacosis.

Keywords: Chlamydia psittaci; Aetiology; community-acquired pneumonia; psittacosis.

Fig. 1.

Selection of publications for the review and meta-analysis.

Fig. 2.

Forest plot of meta-analysis of the proportion of CAP caused by Chlamydia psittaci infections, stratified by type of laboratory diagnosis.

Fig. 3.

Proportion of CAP caused by Chlamydia psittaci in different studies over time and by type of laboratory diagnosis (top panel), and contribution of each type of laboratory diagnosis to the total over time (bottom panel). In the top panel, each symbol represents a study and the according percentage of CAP patients in which C. psittaci was found. The varying colours indicate the diagnostic methods that were used. CF, complement fixation test; IF, immunofluorescence test; ‘unsp.’, unspecified; PCR, polymerase chain reaction. In the bottom panel, the filled colours represent the contribution of each type of laboratory diagnosis to the total over time, expressed in percentages. ‘Year of study’ represents the year in which the gathering of data commenced. Although studies published before 1986 were not included, the period in which patient data had been gathered usually differed from the year of publication.