Clinical Characteristics of Chlamydia psittaci Pneumonia
Chlamydia psittaci pneumonia, also known as psittacosis, is a zoonotic infection caused by the Gram-negative intracellular bacterium Chlamydia psittaci. This condition typically arises from the ingestion of contaminated fecal matter or nasal secretions from infected birds. The severity of human psittacosis ranges from mild flu-like symptoms to life-threatening severe pneumonia. Due to its exclusion from traditional microbiological diagnostic panels, psittacosis is often underreported, misdiagnosed, or inadequately diagnosed. This study retrospectively analyzed the clinical data of 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. The analysis included demographics, symptoms, signs, laboratory tests, disease severity, dynamic computed tomography (CT) findings, tracheoscopy results, treatment responses, and prognosis.
The study enrolled patients who met three inclusion criteria: first, they complied with the criteria for community-acquired pneumonia; second, metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF) revealed specific DNA fragments of C. psittaci; and third, all routine etiological tests, including blood, sputum, BALF smear, and cultures, were negative, with no other causative organisms present. C. psittaci DNA fragments were detected in all five cases, confirming the diagnosis. The mNGS results showed varying copy numbers of C. psittaci nucleic acid in BALF, with C. psittaci being the dominant infection in all cases. One severe case also showed the presence of herpes simplex virus type 1, although its immunoglobulin M was negative, suggesting possible colonization or contamination. Two patients (40%) tested positive for Chlamydia abortus, albeit with low copy numbers, while other patients exhibited low copies of Candida parapsilosis complex, Candida albicans, Staphylococcus epidermidis, Haemophilus influenzae, Burkholderia cepacia, or Acinetobacter baumannii, indicating colonization or contamination.
The study group comprised two females (40%) and three males (60%), with a median age of 65 years (range: 57–71). Among the enrolled patients, two (40%) had hypertension, one presented multiple comorbidities, including hyperlipidemia, hypertension, and pacemaker implantation status, and the remaining three (60%) were healthy. Medical records revealed that three patients (60%) had a history of direct contact with domestic poultry before the onset of the disease. One case involved exposure to pigeon manure, one had newly reared chickens at home, one had reared pigeons, and one had possible indirect environmental contact due to her workplace being located above a farmers’ market that included poultry market areas.
The median time from the onset of the first symptoms to hospital admission was five days (range: 3–7). All five patients presented with high fever. Cough and dyspnea were recorded in three patients each, while fatigue was reported in two patients (40%). One patient experienced nausea and vomiting. Two patients exhibited a relatively slow pulse, and two severe cases displayed mental changes, such as apathy. Moist rales were heard in three patients (60%). Notably, none of the patients complained of headache or muscle soreness, which contrasts with findings from previous reports.
Arterial blood gas analysis revealed type I respiratory failure in three patients (60%). The proportion of neutrophils was increased in all five patients, while white blood cell count was elevated in two. C-reactive protein (CRP) levels were high in all patients, and procalcitonin (PCT) levels were elevated in four cases. CRP and PCT levels were significantly higher in severe cases. Lactate dehydrogenase (LDH) and creatine kinase isoenzyme levels were elevated in all five patients. Hyponatremia was observed in all patients, while hypokalemia and hypocalcemia were recorded in four.
Chest CT findings showed air-containing bronchial shadow consolidation in all five patients (100%). Specifically, scalloped or oval lesions originated from the pleura or interlobar fissures. As the disease progressed, these lesions extended to the hilum and other lobes, including the contralateral lung lobe. In four patients, the lesions originated from the left lower lung. Multi-lobe lesions were observed in two severe cases, while the lesions were confined to one lobe in three non-severe cases. Two patients had minimal pleural effusion. Tracheoscopy revealed no additional secretions in any of the patients.
All five patients were treated with intravenous moxifloxacin (0.4 g once daily) within 24 hours of admission, in combination with β-lactam antibiotics. The three non-severe cases showed improvement within 72 hours. However, the two severe cases experienced aggravated respiratory failure at 76 and 88 hours after admission, requiring intubation and ventilator-assisted breathing in the intensive care unit (ICU). In the ICU, these patients were treated with tigecycline (50 mg every 12 hours, with a first dose of 100 mg) and were eventually cured. This indicates that non-severe cases respond better to moxifloxacin compared to severe cases.
The study has several limitations. First, the small sample size may not fully represent the clinical features of C. psittaci pneumonia. Second, the retrospective nature of the study limits the ability to draw definitive conclusions. Future studies should focus on prospective clinical cases with larger sample sizes to validate these findings.
In conclusion, C. psittaci pneumonia is a significant condition that requires heightened clinical awareness. A history of poultry exposure, high fever, elevated inflammatory biomarkers, elevated LDH levels, and air-containing bronchial shadow consolidation with little or no secretions may guide early clinical diagnosis. Metagenomic sequencing of BALF is a critical diagnostic tool for this condition. Early recognition and appropriate treatment are essential for improving patient outcomes, particularly in severe cases.
doi.org/10.1097/CM9.0000000000001313
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