The study analyzed cases of brucellosis arthropathy recorded at the 940th Hospital in Lanzhou, China, between January 2012 and January 2024. The research was approved by the Scientific Research Management Ethics Committee (Approval No: 2022KYLL301). The positive group consisted of 68 patients, including 46 males and 22 females, with a male-to-female ratio of 2.09. The median age of the patients was 43.1 ± 13.2 years, ranging from 11 to 66 years old. Brucellosis arthropathy accounted for 7.5% of all brucellosis cases during this period. For comparison, a control group of 60 non-infection patients was selected from the same hospital. This group included 23 cases of arthromeningitis, 25 cases of osteoarthritis, 20 cases of rheumatoid arthritis, and 2 cases of gouty arthritis. The male-to-female ratio in the control group was 1.5, and the median age was 51.4 ± 21.9 years.

For the initial admission test, the infection biomarkers were prioritized. Serum samples for procalcitonin (PCT) and C-reactive protein (CRP) were collected in dry tubes with gel separators and centrifuged within the first 2 hours. PCT levels were measured using the E-170 automatic analyzer (Roche), with a cut-off value of 0.046 ng/mL. CRP levels were quantified using an immunoturbidimetric assay on the ARCHITECT c-System (Abbott Laboratories, IL, USA), with a detection limit of 0.5 mg/dL and an imprecision of ≤ 5% total coefficient of variation, as specified by the manufacturer. Synovial fluid samples were collected in EDTA-K2 anticoagulant tubes and analyzed within 2 hours of collection for white blood cell (WBC) count and neutrophil percentage (NEU%) using an automated hematology analyzer (Minray, China). For prevent data duplication, only one set of infection biomarker results per patient was included. Additionally, 60 non-infection patients from the hospital were selected as the control group for comparison of infection biomarkers. This approach ensured a standardized and accurate assessment of infection biomarkers in both brucellosis and control groups.

The Standard Tube Agglutination Test (SAT) and Rose Bengal Test (RBT) antigens were obtained from the Institute of Infectious Diseases, China Center for Disease Control and Prevention. For the RBT, a card agglutination method was used. A total of 0.03 mL of the tested serum was mixed with 0.03 mL of the antigen, and the results were observed within 4 minutes. A reaction above “+” was considered positive. For the SAT, serial 2-fold dilutions of the patient’s serum (ranging from 1:12.5 to 1:400) were mixed with Brucella antigen in the wells of a microtiter plate. The plate was incubated at (37 ± 1) °C for 24 hours. After incubation, the results were compared with a turbidimetric control tube. A titer of ≥1:100 (++) was considered diagnostic. For patients with a disease course of more than one year, a titer of ≥1:50 (++) was also considered diagnostic.

Clinical diagnosis based on Brucella culture positive, epidemiological history, and laboratory test results.

Statistical analysis was performed using SPSS 22.0 software. For measurement data (e.g., age, PCT, CRP, WBC, and NEU%), variables with a normal distribution were expressed as median (M) with interquartile range (P25, P75). The levels of PCT and CRP, which were non-normally distributed, were also expressed as M (P25, P75), and the Mann-Whitney U test was used for comparison. For enumeration data (e.g., gender), results were expressed as rates, and the χ² test was applied. A p-value < 0.001 was considered statistically significant. The general information comparing the infection group and control group is summarized in Table 1 . Additionally, the sensitivity and specificity of clinical infection biomarkers in the infection and control groups were analyzed using the receiver operating characteristic (ROC) curve, with the area under the ROC curve (AUC) calculated to evaluate diagnostic performance.

In this study, the median age of patients with human brucellosis arthropathy was 43.1 ± 13.2 years, with an age range of 11 to 66 years. The male-to-female ratio was 2.09, and brucellosis arthropathy accounted for 7.5% of the total brucellosis cases in the hospital. Among the 68 cases of joint brucellosis, all patients were treated with a combination of doxycycline and rifampicin for 3 months. Additionally, 34% of these patients underwent surgical treatment. The prognosis was satisfactory, as illustrated in Figure 1A .

Data from 68 cases of brucellosis in our hospital from 2012 to 2024 were analyzed. Among these, 23 cases were culture-positive and identified as Brucella melitensis using automated instruments. Joint fluid-blood bottle culture was the primary diagnostic method in 15 cases (62.2%,15/23), with all positive cultures detected in aerobic bottles within an average time of 74.8 ± 17.9 hours (n=22 bottles), ranging from 41 to 110 hours. Blood culture and joint tissue culture accounted for 40.9% and 4.5% of the cases, respectively. The diagnostic methods and their sensitivity were as follows: Brucella spp. Culture: 69.7% (23/33). Standard Tube Agglutination Test (SAT): 87.7% (50/57), Rose Bengal Test (RBT): 91.2% (52/57). The distribution of diagnostic approaches was: Pathogenic diagnosis (culture): 33.8% (23/68), Serological diagnosis (SAT/RBT): 55.8% (40/68), Clinically suspected diagnosis: 7.4% (5/68). The sensitivity of combining all three detection methods (culture, SAT, and RBT) was 2.6% (63/68), as illustrated in Figure 1B .

In cases of brucellosis arthropathy, the main site of infection was the knee joint, accounting for 64.7% of cases. This was followed by the hip joint (20.6%), sacroiliac joint (10.3%), and other joints (11.1%). Multi-joint infection was observed in 7.4% of cases, as illustrated in Figure 2 . In 58 cases joint image display septic arthritis at 20.7%, joint effusion at 31.0%, bone destruction at 12%, degenerative changes at 10.3%, normal at 10.3%, and PJI (prosthetic joint infection) at 6.9%.

Between 2012 and 2024, 68 cases of brucellosis-associated arthropathy were documented with a median infection duration of 90 days (IQR 30-343). Within this cohort, 19 cases (27.9%) progressed to chronic brucellar arthritis, defined by persistent joint pain and functional impairment (including restricted range of motion) lasting ≥6 months. These chronic cases demonstrated substantially prolonged disease courses, with a median duration of 540 days (IQR 365-1460) and clinical manifestations persisting from 6 months to 10 years. The temporal progression patterns of these cases are visually summarized in Figure 3 .

The discriminatory ability for brucellosis as determined by the AUC-ROC for each biomarker is presented in Figure 4 . For overall biomarkers, the AUC-ROC value for CRP was 0.792, and when the cut-off value of 4.07 mg/ml, the sensitivity and specificity were 0.842 and 0.722 respectively, and the U test also indicated CRP had a significant difference, Z=5.568, p<0.001 presented in Table 1 and Table 2 . And there were no significant differences regarding age, sex Joint fluid -WBC and, joint fluid -NEU% distribution between the Infection group and the Control group.

We found that joint fluid-blood bottle culture, a key diagnostic method for brucellosis arthropathy, has not been widely adopted due to limited sample size in clinical practice. In our hospital, we have reported cases of chronic brucellosis arthropathy; however, the latent infection rate of brucellosis arthropathy has not been systematically calculated. Additionally, due to biosafety concerns, routine antimicrobial susceptibility testing for Brucella spp. is not feasible in our setting.

Our findings demonstrate that joint fluid-blood bottle culture is an effective method for culturing brucellosis arthropathy specimens, significantly improving the positive rate of etiological diagnosis. Given its diagnostic efficacy, this technology warrants wider application in clinical practice.