Key points in the diagnosis and treatment of acute respiratory failure caused by Chlamydia psittaci pneumonia
Authors: Zhou Changqing , Li Shuangmei , Hong Yinghui , Sheng Yue , Jing Rui , Fu Jiaying 
Published: July 2023

Abstract
Background
Psittacosis, a lung infection caused by Chlamydia psittaci (C. psittaci), is a rare cause of community-acquired pneumonia, and its clinical presentation can range from asymptomatic cases to severe cases complicated by respiratory failure (RF) or even systemic multi-organ failure. Although psittacosis has been increasingly recognized and reported in recent years, the diagnosis and treatment of acute RF (ARF) due to C. psittaci pneumonia are less frequently reported. Metagenomic next-generation sequencing (mNGS) has been used to aid in diagnosis, but its correlation with disease severity remains unclear. Therefore, it is necessary to investigate the pathogenesis and key points in the diagnosis and treatment of ARF caused by C. psittaci pneumonia.
Methods
We reviewed the patients with C. psittaci pneumonia complicated by ARF, who were admitted to the emergency intensive care unit and intensive care unit of the Eighth Affiliated Hospital of Sun Yat-sen University from August 2019 to April 2021. Their clinical data were collected, and the diagnosis, treatment, and prognosis were analyzed. Additionally, linear regression analysis was used to evaluate the correlation of C. psittaci reads sequenced by mNGS with serum inflammatory indicators, Sequential Organ Failure Assessment (SOFA) score at admission, Acute Physiology and Chronic Health Evaluation II (APACHEII) score at admission, and arterial partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) ratio.
Results
Five patients with C. psittaci pneumonia complicated by ARF were included. Specifically, one case was complicated with severe pneumonia, two cases with acute respiratory distress syndrome (ARDS), and two cases with bronchial sputum obstruction. Two patients with bronchial sputum obstruction were subjected to bronchoscopic removal of mucus plugs, and PaO2/FiO2 ratio was restored to above 300 mmHg. The PaO2/FiO2 ratio of the remaining three patients showed gradual improvement after three and five days of non-invasive mechanical ventilation. Two cases showed no response to azithromycin and levofloxacin, respectively, but the infection was effectively controlled after changing the antibiotic to doxycycline. Except for the two patients with antibiotic regimen change, one of the remaining three patients was treated with doxycycline, and two with levofloxacin, and their infection was also effectively controlled. All the five patients had a good prognosis after treatment. The number of C.psittaci sequence reads had no significant correlation with serum inflammatory indicators, SOFA score at admission, PaO2/FiO2 ratio, and APACHEII score at admission.
Conclusions
Patients with C. psittaci pneumonia-caused ARF are usually combined with severe pneumonia, ARDS and bronchial sputum obstruction. mNGS can be used as an aid to diagnosis. Patients have a good prognosis after treatments such as anti-infection and non-invasive mechanical ventilation. The number of C. psittaci sequence reads cannot be used to reflect the severity of the disease and inflammation in patients with ARF.