Community-acquired Pneumonia Due to Chlamydia Pneumoniae

This international retrospective Franco-Swiss study focuses on community-acquired pneumonia (CAP) caused by Chlamydia pneumoniae. The working hypothesis is that the prevalence of C. pneumoniae pneumonia is overestimated by the medical community. The primary objective is to determine the true prevalence of C. pneumoniae infections among patients with pneumonia who underwent simplex or multiplex PCR testing. Secondary objectives include;1)Outpatient management2)Hospitalization in a medical ward3)Admission to the intensive care unit4) In-hospital mortality5) Radiological presentation of patients with community-acquired pneumonia (CAP) caused by Chlamydia pneumoniae 6)Prevalence of viral or bacterial co-infections associated with C. pneumoniae CAP

Detailed Description We have all learned and continue to teach that community-acquired pneumonia (CAP) is essentially represented by three bacteria: Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydia pneumoniae. While the recent Mycoplasma outbreak in France and the prevalence of severe Legionella infections in intensive care units confirm the real impact of these pathogens in CAP, the low number of Chlamydia pneumoniae cases documented by PCR raises questions.Over the past twenty years, the development of highly sensitive molecular tests (specific PCR or multiplex PCR targeting intracellular respiratory pathogens) has made it possible to precisely detect Chlamydia pneumoniae and to confirm or rule out its presence in the respiratory tract of patients with pneumonia.We are therefore conducting a retrospective study between France and Switzerland to determine, on the one hand, the number of CAP cases due to Chlamydia pneumoniae confirmed by PCR, and on the other hand, to better characterize the phenotype of these patients.

Primary outcomes

• Prevalence of Chlamydia pneumoniae Among Pneumonia Cases Tested by PCR [January 2015 to December 2025]: Proportion of pneumonia cases with a positive simplex or multiplex PCR for Chlamydia pneumoniae among all patients who underwent respiratory PCR testing during the study period.

Secondary outcomes

• Clinical Severity of Chlamydia pneumoniae Pneumonia [From hospital admission through hospital discharge (up to 90 days)]: Distribution of patients according to outpatient management, hospitalization in a medical ward, admission to intensive care, and in-hospital mortality.
• Radiological Characteristics [Baseline (at the time of pneumonia diagnosis)]: Chest radiograph and chest computed tomography findings associated with PCR-confirmed Chlamydia pneumoniae pneumonia.
• Viral Co-Infection Rate [Baseline (at the time of PCR testing)]: Proportion of patients with concomitant viral infection identified by microbiological testing.
• Bacterial Co-Infection Rate [Baseline (at the time of PCR testing)]: Proportion of patients with concomitant bacterial infection identified by microbiological testing.
• Length of Hospital Stay [From hospital admission through hospital discharge (up to 90 days)]: Duration of hospitalization among admitted patients.

Sex: All

Inclusion Criteria:

* Positive simplex or multiplex PCR for Chlamydia pneumoniae on an upper or lower respiratory tract specimen between January 2015 and December 2025.
* Availability of clinical data allowing confirmation of pneumonia diagnosis.

Exclusion Criteria:

* Patient opposition to the use of medical data for research purposes.
* Absence of pneumonia diagnosis.
* Insufficient clinical data for analysis.

• Results publication: Garin N, Hugli O, Genne D, Greub G. Lack of Chlamydia-related bacteria among patients with community-acquired pneumonia. New Microbes New Infect. 2015 Oct 22;8:164-5. doi: 10.1016/j.nmni.2015.10.002. eCollection 2015 Nov. No abstract available. PMID 27257497
• Results publication: Garin N, Marti C, Skali Lami A, Prendki V. Atypical Pathogens in Adult Community-Acquired Pneumonia and Implications for Empiric Antibiotic Treatment: A Narrative Review. Microorganisms. 2022 Nov 24;10(12):2326. doi: 10.3390/microorganisms10122326. PMID 36557579
• Results publication: Miyashita N. Atypical pneumonia: Pathophysiology, diagnosis, and treatment. Respir Investig. 2022 Jan;60(1):56-67. doi: 10.1016/j.resinv.2021.09.009. Epub 2021 Nov 5. PMID 34750083
• Results publication: Cunha BA. The atypical pneumonias: clinical diagnosis and importance. Clin Microbiol Infect. 2006 May;12 Suppl 3:12-24. doi: 10.1111/j.1469-0691.2006.01393.x. PMID 16669925