Identification and comparison of Chlamydia psittaci, Legionella and Mycoplasma pneumonia infection

Conventional etiological detection and pathogenic antibody methods make it challenging to identify the atypical pathogens among the community-acquired pneumonia (CAP). Metagenomic next-generation sequencing (mNGS) could rapidly detect all potentially infectious diseases and identifies novel or potential pathogens.

Eighteen patients diagnosed with atypical CAP were enrolled in this retrospective study, including nine Chlamydia psittaci pneumonia (C. p), four Legionella pneumonia (L. p) and five Mycoplasma pneumonia (M. p). We simultaneously tested bronchoalveolar lavage fluid (BALF) samples for conventional microbiological methods and mNGS, and blood specimens were analysed. We also collected and compared baseline and clinical characteristics and treatment responses.

Patients with C. p and L. p had similar symptoms, including fever, cough, headache, dyspnoea, asthenia, shivering and headache, compared with M. p, whose symptoms were slight. C. p and L. p usually showed multiple lobar distributions with pleural effusion. Serologic testing indicated that L. p had higher levels of white blood cells (WBCs), neutrophils, C-reactive protein (CRP), procalcitonin (PCT), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and creatinine compared with M. p and L. p (p < 0.05). However, patients with C. p had lower levels of albumin (p < 0.05), and M. p had a minimum risk of cardiac volume loads (p < 0.05). CD4/CD8 ratio, lymphocytes, aspartate aminotransferase (AST), creatine kinase (CK), cell counting of BALF and coagulation had no difference (p < 0.05). Pathogenic IgM assay showed that 4/5 cases were positive for M. p and no positive detection for C. p and L. p infection. We timely adjusted the antibiotics according to the final mNGS results. Eventually, 16/18 patients recovered fully. Conditions of L. p patients were worse than those of C. p patients, and those of M. p patients were the least.

Early application of mNGS detection increased the atypical pathogenic identification, improved the prognosis and made up for the deficiency of conventional detection methods.