Unveiling the Clinical Characteristics of Chlamydia psittaci Pneumonia

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Unveiling the Clinical Characteristics of Chlamydia psittaci Pneumonia

Psittacosis, caused by Chlamydia psittaci, a Gram – negative intracellular bacterium, is a zoonosis. Ingestion of contaminated fecal matter and nasal secretions from infected birds leads to this condition. The severity of human psittacosis can range from mild flu – like symptoms to life – threatening severe pneumonia. However, due to C. psittaci not being part of traditional microbiological diagnosis, human psittacosis is often underreported, misdiagnosed, and inadequately diagnosed. This study, published in the Chinese Medical Journal in 2021, aimed to retrospectively analyze the clinical data of C. psittaci pneumonia patients.

Introduction

Psittacosis is a disease that can have significant implications for public health. Given its zoonotic nature and the challenges in its diagnosis, understanding its clinical characteristics is crucial. This study focused on five consecutive cases of C. psittaci pneumonia admitted to The Fourth Affiliated Hospital of Zhejiang University School of Medicine between December 2019 and May 2020.

Study Design and Methods

Patient Selection

Patients had to meet three inclusion criteria: they complied with criteria for community – acquired pneumonia, metagenomic next – generation sequencing (mNGS) from bronchoalveolar lavage fluid (BALF) revealed a specific deoxyribonucleic acid (DNA) fragment in C. psittaci, and all routine etiological tests (blood, sputum, BALF smear, and cultures) were negative with no other causative organisms.

Data Collection

Data on demographics, symptoms, signs, laboratory tests, disease severity, dynamic computed tomography, tracheoscopy, and clinical course were extracted. Treatment prescription, response, and prognosis were also collected. The study was approved by the Ethics Committee, and informed consent was obtained from patients.

Results

Microbiological Findings

C. psittaci DNA fragments were detected in all cases. In one severe case, herpes simplex virus type 1 was also detected (but immunoglobulin M was negative, suggesting possible colonization or pollution). Two patients were positive for Chlamydia abortus (low copy numbers), and other patients had low copies of various organisms like Candida parapsilosis complex, Candida albicans, etc., indicating colonization or pollution.

Demographics

The study group had two females (40%) and three males (60%), with a median age of 65 (57 – 71) years. Two patients had hypertension, one had multiple diseases (hyperlipidemia, hypertension, and pacemaker implantation), and three were healthy. Three patients had a history of direct contact with domestic poultry before the disease onset.

Clinical Symptoms and Signs

  • Symptoms: High fever was present in all five patients. Cough and dyspnea were in three patients each. Fatigue was in two (40%) patients. One patient had nausea and vomiting.
  • Signs: Relatively slow pulse was in two patients. Mental changes (apathy) were in two severe patients. A few moist rales could be heard in three patients (60%).

    Laboratory Tests

  • Blood Gas Analysis: Type I respiratory failure in three patients (60%).
  • Inflammatory Markers: Neutrophil proportion increased in five patients, white blood cell count increased in two. C – reactive protein (CRP) was high in five patients, procalcitonin (PCT) elevated in four (higher in severe cases).
  • Enzymes: Lactate dehydrogenase (LDH) and creatine kinase isoenzyme elevated in all five.
  • Electrolytes: Hyponatremia in five, hypokalemia and hypocalcemia in four.

    Imaging and Tracheoscopy

  • Chest CT: Air – containing bronchial shadow consolidation in all five (100%). Lesions originated from pleura or interlobar fissures (scalloped or oval). Progressed to involve hilum and other lobes. Left lower lung origin in four. Multi – lobe lesions in two severe cases, single – lobe in three non – severe. Two patients had a little pleural effusion.
  • Tracheoscopy: All five patients were clean with no additional secretions.

    Treatment

    All patients received intravenous moxifloxacin (0.4g, once a day) within 24 hours of admission, combined with β – lactam antibiotics. Three non – severe cases improved within 72 hours. Two severe cases had aggravated respiratory failure (76 and 88 hours after admission), were intubated, and admitted to ICU. In ICU, they received intravenous tigecycline (50mg, first dose 100mg every 12h) and were cured.

Discussion

Limitations

The study had a small sample size, which may not fully represent the clinical features. It was also a retrospective study. Future studies should use larger samples and be prospective.

Clinical Implications

  • Diagnosis: History of poultry exposure, high fever, elevated inflammatory biomarkers (CRP, PCT), elevated LDH, and air – containing bronchial shadow consolidation with little or no secretions (as seen in imaging) can guide early diagnosis. Metagenomic sequencing of BALF is an important diagnostic method.
  • Treatment: Non – severe cases responded well to moxifloxacin, while severe cases needed additional treatment like tigecycline.

Conclusion

C. psittaci pneumonia has distinct clinical characteristics. Understanding these can aid in early diagnosis and appropriate treatment. Further research with larger samples is needed to confirm and expand these findings.

doi.org/10.1097/CM9.0000000000001313

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