A 51-year-old male patient was admitted in March 2025 due to fever without obvious inducement

accompanied by sore throat

cough and yellow sputum. He had a history of chronic lymphocytic leukemia(CLL) for more than one year. C-reactive protein (CRP)

>

200 mg/L was detected in an outside hospital

and anti-infective treatment with ceftriaxone failed to improve his symptoms. After admission

relevant examinations showed elevated hypersensitive C-reactive protein(hs-CRP) and procalcitonin(PCT)

abnormally increased liver enzymes and creatine kinase (CK)

as well as multi-system injuries such as hyponatremia-hypochloremia and hypoalbuminemia. The results of routine etiological screening and blood culture were negative. Bone-marrow aspiration and imaging examinations indicated stable bone-marrow manifestations of CLL

with only pulmonary infectious lesions and mildly enlarged lymph nodes

and no typical B-symptoms or extranodal invasion

so the progression of CLL was excluded. Bronchoalveolar lavage fluid was collected for targeted next-generation sequencing(tNGS)

and

Chlamydia psittaci

(Cps) was detected with a high sequence number. After supplementary epidemiological history-taking

pigeon-exposure before disease onset was confirmed

and Cps infection was diagnosed. Cephalosporin antibiotics to which the pathogen was resistant were discontinued during treatment. Enhanced anti-infective therapy with doxycycline combined with moxifloxacin was administered

and the patient’s condition and laboratory indicators were dynamically monitored. After treatment

the patient’s body temperature returned to normal

all inflammatory markers decreased significantly

and pulmonary infectious lesions were absorbed. This case highlights the diagnostic value of tNGS for difficult-to-diagnose atypical-pathogen infections in immunocompromised hosts and verifies the importance of detailed epidemiological history collection

which can provide a reference for the diagnosis and treatment of similar clinical cases.