Objective  To detect Brucella genomic DNA copy number in blood samples from brucellosis by a nested-polymerase chain reaction assay (nested-PCR). The relationship of Brucella DNA copy number with antibody level and clinical symptoms in brucellosis were analyzed.

  Methods  The suspected brucellosis in outpatient department were investigated, the information about their clinical symptoms, exposure and medical history were recorded, and blood samples were collected from them. The Brucella antibody were detected by serum agglutination test (SAT). Brucellosis was diagnosed according to “Brucellosis Diagnosis Criteria” (WS 269—2019). Bacterial genomic DNA was extracted. The genomic DNA of Brucella was detected by nested-PCR assay. The relationship of Brucella DNA copy number with antibody levels and clinical symptoms of brucellosis were analyzed by statistical methods.

  Results  In 118 confirmed brucellosis cases, 78 were men, 40 were women. The clinical symptoms included fever, fatigue, headache, chest and back pain, low back pain, limb pain, joint-muscle pain, sweating and testicular pain. In the 118 cases of brucellosis, the Brucella DNA positive rate was 63.56% (75/118) in the anticoagulant whole blood. The median (MED) of Brucella DNA copy numbers were 7 copies/mL in blood, and the interquartile range (IQR) was 2−17 copies/mL in blood. The positive rate of SAT was 38.14% (45/118) in the 118 cases. The new cases and revisited cases accounted for 55.08% (65/118)and 44.92% (53/118) respectively in 118 cases. The positive rates of Brucella DNA were 72.31% (47/65) and 52.83% (28/53) in new cases and revisited cases respectively. The MED of Brucella DNA copy numbers were 3 copies/mL in blood, the IQR was 2−26 in 47 new cases. The MED of Brucella DNA copy numners were 4 copies/mL in blood, the IQR was 2−12 copies/mL in blood in 28 revisited cases.

  Conclusion  In suspected brucellosis patients, attention should be paid to those with joint-muscle pain. The PCR detection was helpful in the diagnosis of early infection of Brucella or brucellosis patients with negative SAT results. The combination of Brucella DNA detection and serological examination could facilitate the diagnosis of brucellosis.