18 January 2026
: Case report 
Multi-Pathogen Knee Infection, Including Treponema pallidum and Brucella: A Case Report
Challenging differential diagnosis, Rare disease, Clinical situation which can not be reproduced for ethical reasons
Youhan Yang
ABCDEF 1, Haitao Chen ADEF 1, Yinxian Wen ACDE 1, Qinglong Chai BCE 1, Yi Hua BEF 1, Xu Yang ACDEF 1*, Liaobin Chen ADG 1
DOI: 10.12659/AJCR.950156
Am J Case Rep 2026; 27:e950156
Table 1 Selected laboratory test results.
| Type of specimen | Content of inspection | Results | Normal value |
|---|---|---|---|
| ESR | 38 mm/h | 0–15 mm/h | |
| PCT | <0.05 ng/mL | <0.05 ng/mL | |
| IL-6 | 2.87 pg/mL | 0–7 pg/mL | |
| hs-CRP | 13.94 mg/L | 0–3 mg/L | |
| RPR | Titer 1: 8 (+) | negative | |
| TP-AB | 19.82 s/co | 0–1 s/co | |
| TPHA | 26.66 s/co | 0–1 s/co | |
| Brucellosis IgG | Positive | Negative | |
| Brucellosis IgM | negative | Negative | |
| TB-IGRA | Positive | Negative | |
| XpertMTB RIF | Negative | Negative | |
| Negative | Negative | ||
| Character | Red bloody fluid | Clear and transparent | |
| Synovial fluid culture (aerobic) and drug sensitivity | After 5 days of cultivation, no bacteria grew | / | |
| Joint fluid culture (anaerobic) and drug sensitivity | After 5 days of cultivation, no bacteria grew | / | |
| Fungiculture | After 5 days of culture, no fungi were cultivated | / | |
| Acid-fast stain | Negative | Negative | |
| NGS | (+) | / | |
| Character | Clear and transparen | Clear and transparent | |
| NGS | TP-Ab 20.82 s/co | 0–1 s/co | |
| Hepatitis B surface antigen | 0.00 | 0–0.05 IU/mL | |
| Anti-HCV | 0.10 | 0–1.00s/co | |
| Anti-AIDS antigen | 0.19 | 0–1.00s/co | |
| HCV core antigen | 0.00 | 0.00–2.99 fmol/L | |
| DNA of herpesvirus hominis | Negative | / | |
| DNA of cytomegalovirus | Negative | / | |
| DNA of EBV | Negative | / | |
| Gram stain for bacteria | No bacteria were detected | / | |
| Acid-fast stain | Acid-fast bacilli were not detected | / | |
| Ink dyeing | No was detected | / | |
| / | None | / | |
| / | Normal | / | |
| Protein | 4.7 | 20–40 g/L | |
| LDH | 1540 | 230–460 U/L | |
| ESR – erythrocyte sedimentation rate; PCT – procalcitonin; IL-6 – interleukin-6; hs-CRP – high-sensitivity C-reactive protein; RPR – rapid plasma reagin circle card test; TP-AB – antibody; TPHA – hemagglutination assay; IgG – immunoglobulin G; IgM – immunoglobulin M; TB-IGRA – interferon-gamma release assay; PPD – purfied protein derivative; NGS – next-generation sequencing; CSF – cerebrospinalfluid; HCV – gepatitis C virus; AIDS – acquired immunodeficiency syndrome; EBV – Epstein-Barr virus; LDH – lactate dehydrogenase. | |||