# Comparison of clinical features between Chlamydia psittaci and Legionella

## TL;DR

This study compares clinical features of pneumonia caused by Chlamydia psittaci and Legionella, highlighting how next-generation sequencing can improve diagnosis.

## Contribution

Identifies key clinical and laboratory differences between C. psittaci and Legionella pneumonia using NGS data.

## Key findings

- C. psittaci pneumonia is associated with poultry exposure, relative bradycardia, and elevated ALT, AST, and CK levels.
- NGS improves early diagnosis of atypical pneumonia by distinguishing between C. psittaci and Legionella infections.
- Multivariate analysis shows underlying diseases, rural residence, and LMR are significant differentiators between the two pneumonias.

## Abstract

Traditional diagnostic methods have difficulty distinguishing between Chlamydia psittaci (C. psittaci) pneumonia and Legionella pneumonia (L. pneumonia). This study aims to delineate the differences between C. psittaci pneumonia and L. pneumonia.

This retrospective analysis included 71 cases of C. psittaci pneumonia and 21 cases of L. pneumonia, all confirmed via next-generation sequencing (NGS). We systematically collected and compared data on clinical characteristics, laboratory findings, chest CT imaging, bronchoscopic observations, and prognostic outcomes between the two groups.

In the C. psittaci pneumonia cohort, 64 patients (91.4%) had an opportunity to contact with poultry, with a maximum temperature of mean 39.6 °C. Additionally, 23 patients (32.4%) experienced dyspnea, and 57 patients (80.3%) exhibited relative bradycardia. Compared to patients with L. pneumonia, those with C. psittaci pneumonia had lower leukocyte counts, neutrophil counts, mononuclear cell counts, systemic inflammatory response index (SIRI), and urea levels, while lymphocyte-to-monocyte ratio (LMR), glutamic-pyruvic transaminase (ALT), glutamic oxaloacetic transaminase (AST), and creatine kinase (CK) levels were elevated. Next-generation sequencing (NGS) plays a crucial role in the early diagnosis of infectious pathogens. Multivariate analysis revealed differences in underlying diseases, residing in countryside, relative bradycardia, and LMR between the two groups.

Several characteristics aid in differentiating C. psittaci pneumonia from L. pneumonia, including exposure to poultry, relative bradycardia, some infection indicators, ALT, AST, and CK. NGS addresses the limitations of traditional diagnostic methods. The early application of NGS facilitates the diagnosis of atypical pneumonia. Multivariate regression analysis suggested that underlying diseases, residing in countryside, relative bradycardia, and LMR is significant in differentiating C. psittaci pneumonia and L. pneumonia.