A 13-year-old boy was admitted to our hospital due to an intermittent fever for 12 days. Prior to this, the patient was perfectly healthy. It was confirmed by the patient and his relatives, that he had recently been in contact with a kitten but not with pigeons, sheep, or other animals. Prior to fever onset, the patient experienced some shivers and then went on to develop headaches during the fever episodes, a poor appetite, and weight loss. He had been given various antimicrobial drugs before being admitted to our hospital, but none of them proved effective. The boy's temperature gradually rose to 40.2  C, and the feverish episodes became more frequent; thus, the patient's relatives asked for him to be admitted to our hospital.
According to the admission records, the patient initially had a temperature of 38.2  C, with the fever occurring once a day. The patient experienced no other discomfort such as a cough, vomiting, diarrhea, rash, arthralgia, headache, or convulsion. Laboratory examination (performed in a local hospital) showed that the patient's complete blood count and the immune function were normal. However, they did detect an increase in the serum C-reactive protein (CRP) levels to 54.08mg/L (normal 0-5 mg/L) and in the erythrocyte sedimentation rate (ESR) to 23 mm/h (normal 0-20 mm/h). Chest computed tomography (a CT scan) showed the presence of small nodules on the upper lobe of the right lung and on the lower lobes of both lungs, with a maximum diameter of about 4 mm. An ultrasound detected splenomegaly; the spleen was about 126 mm long and 40 mm thick. Etiological examination revealed no abnormalities, including mycoplasma, respiratory syncytial virus, Epstein-Barr virus, or Coxsackie virus. A lumbar puncture was performed, but no abnormality was detected in the patient's cerebrospinal fluid.
At admission, the physical examination identified no positive signs. Although the ultrasound performed at the local hospital showed an enlarged spleen, it was not palpable at the left costal margin. The laboratory investigations on the first day of admission showed a significant increase in serum CRP (94.73 mg/L), and an ESR of 78 mm/h. The procalcitonin concentration was 0.285 ng/mL (normal 0-0.02 ng/mL). Other laboratory tests, including complete blood count, blood biochemical examination, coagulation test, and thyroid function, were all within the normal range. All other laboratory test results also came back negative; these included HIV infection, tuberculosis, other viral infections (e.g., cytomegalovirus, herpes simplex virus, hepatitis virus, influenza virus, among others), galactomannan test, connective tissue disease antibody test, tumor markers, two sets of blood cultures for the detection of aerobic and anaerobic bacteria, and bone marrow cytology and culture tests. Furthermore, echocardiography, a chest CT scan, and cranial magnetic resonance imaging (MRI) failed to detect noticeable abnormalities.
During the initial phase of treatment, the patient received empiric antimicrobial drugs such as latamoxef sodium, rifamycin, and penciclovir for four days. However, the fever persisted and the CRP levels and ESR rose to 107.58 mg/L and 98 mm/h, respectively. On the fifth day after admission, metagenomic next-generation sequencing (mNGS) was performed on the patient's peripheral blood, using an Illumina Next 550 sequencer with a single-end 75 base pair sequencing strategy. A total of 19,446,948 reads were generated within 24 h. After quality control, 19,186,121 were aligned with the human reference genome (HG38) and 260,404 reads were used for downstream analysis. Finally, four B. henselae-specific sequences were detected. Since neither our hospital nor the Henan Center for Disease Control could perform serological antibody tests or polymerase chain reaction (PCR) for B. henselae, we carried out another blood culture but this time extended the culture period to six weeks. The patient's treatment plan was adjusted, and the following antibiotics were administered: azithromycin (500 mg on the first day and 250 mg on the second to fifth days) together with rifampin (20 mg/kg/d, given in two doses), followed by doxycycline (200 mg/d, given in two doses) with rifampin. The fever gradually subsided and the shivering and headaches eventually disappeared. The patient's CRP levels also decreased and his temperature returned to normal on the 17th day after admission. The patient was feeling well enough to be discharged on the 19th day. He continued to take doxycycline and rifampin orally for the entirety of the one-month-long course. When the patient returned to our hospital for a follow-up reexamination, he was in good health. No abnormalities were detected in his blood after the following tests were performed: complete blood count, CRP, ESR, procalcitonin concentration, blood biochemical examination, and mNGS. We were therefore able to discontinue the patient's treatment. The patient's follow-up prolonged blood culture remained negative for B. henselae.