Psittacosis Pneumonia Features, Distinguishing Characteristics, and Outcomes: A Retrospective Study

Abstract

Purpose: Psittacosis is an often-neglected cause of community acquired pneumonia (CAP). The limited diagnostic methods for psittacosis pneumonia invariably result in an unfavourable prognosis. Consequently, the early detection of psittacosis pneumonia is crucial. This study aimed to analyse the characteristics, clinical features and treatments of the patients to improve early diagnosis and outcomes.

Patients and methods: We retrospectively analyzed the clinical features and outcomes of 52 cases of psittacosis pneumonia diagnosed with next-generation sequencing (NGS) from January 2022 to August 2024 in a local tertiary hospital in China.

Results: Of the 52 patients, 18 had a clear exposure to poultry or birds. The main clinical manifestations included fever (100%, 52/52), cough (75.0%, 39/52), fatigue (57.7%, 30/352), and dyspnea (36.5%, 19/52). Significant elevations in neutrophil counts (NEUT), C-reactive protein (CRP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), D-dimer, lactate dehydrogenase (LDH), creatine kinase (CK), interleukin-6 (IL-6) and interferon-γ (IFN-γ), as well as reductions in lymphocyte (LY) and albumin (ALB) were observed. The main chest computed tomography (CT) features were consolidated. Eight patients diagnosed with severe CAP (SCAP) exhibited higher NEUT, CRP, procalcitonin (PCT), blood urea nitrogen (BUN), creatinine, D-Dimer and IL-6 levels, as well as lower oxygen index. The interval between the onset of symptoms and diagnosis was 6-34 days. C. psittaci infection was identified by metagenomic NGS (mNGS) or targeted NGS (tNGS) in all cases, and the average length of hospital stay for these patients was 9.4 days. Following the identification of the aetiology, all patients were promptly initiated on tetracycline- or fluoroquinolone-based therapy, with complete recovery observed in all cases.

Conclusion: Patients exposed to poultry should be alert to Chlamydia psittaci pneumonia. The application of NGS has improved the diagnostic accuracy of C. psittaci pneumonia, reduced unnecessary use of antibiotics, and shortened the course of disease. Patients who received tetracycline-based therapy showed a good prognosis.

Keywords: Chlamydia psittaci; community acquired pneumonia; next-generation sequencing; tetracyclines.

Figure 1

Chest computed tomography (CT) images of representative cases with psittacosis infection. Chest CT findings of a patient with multiple lobar consolidation are shown in (A) and (B). Chest CT findings of a patient with lobar consolidation, pleural effusion and nodule-like patchy consolidation are shown in (C) and (D). Chest CT findings of a patient with unilateral lobar consolidation are shown in (E) and (F).