The relationship between C. psittaci infection and respiratory failure based on respiratory microbiota analysis: a retrospective cohort study.

OBJECTIVES: This study aimed to explore the impact of the pulmonary microbiota on the occurrence of respiratory failure in patients with psittacosis pneumonia. METHODS: A total of 20 patients diagnosed with psittacosis pneumonia were enrolled in this study. Patients were divided into two groups according to the presence or absence of respiratory failure at admission. Clinical data, laboratory findings, and bronchoalveolar lavage fluid analyses were collected. Next-generation sequencing was employed to analyze the pulmonary microbiota. RESULTS: In this cohort, patients with respiratory failure exhibited a significantly higher relative abundance sequences of C. psittaci compared with those without respiratory failure. Notably, Spearman correlation analysis indicated a significant negative correlation between C. psittaci relative abundance of sequences and CD4+ T-lymphocyte counts (r = -0.870, p = 0.002) and a positive correlation with the pulmonary arteriovenous oxygen partial pressure difference (r = 0.728, p = 0.017). Further analysis of the bacterial communities showed a negative association between Pseudomonas and C. psittaci (r = -0.509, p = 0.031), whereas Veillonella was positively correlated with C. psittaci (r = 0.533, p = 0.023). CONCLUSIONS: The relative abundance sequences of C. psittaci was significantly higher in patients with respiratory failure than in those without respiratory failure, suggesting an association between C. psittaci load and disease severity. The significant negative correlation between relative abundance sequences of C. psittaci and CD4+ T-lymphocyte count suggests that C. psittaci may exacerbate disease progression by compromising the host immune response, but direction of this relationship cannot be determined. Furthermore, the negative correlation between the relative abundance sequences of Pseudomonas and C. psittaci suggests a possible competitive or protective interaction between these two organisms. In contrast, the positive correlation between Veillonella and C. psittaci may indicate a shared ecological niche. These findings provide preliminary evidence of a relationship between lung microbiota composition and the severity of psittacosis pneumonia, while the causal mechanisms remain to be elucidated in future studies.