Sensitivity of current laboratory methods for brucellosis diagnosis at endemic foci

Brucella is an intracellular pathogen that can infect both animals and humans. Brucellosis is one of the most important zoonotic diseases and a global public health problem. In this study, 800 blood and serum samples were collected during 2021–2022 from suspected brucellosis patients with clinical symptoms, fever and chills, night sweats, recurrent and prolonged fever, weight loss, anorexia, and joint inflammation at medical centers in eastern and northeastern cities of Iran. The laboratory procedures were conducted between 2021 and 2023. The samples were evaluated via the culture method, Wright, 2-mercaptoethanol, Enzyme Linked Immuno Sorbent Assay, Polymerase Chain Reaction for the 16 S rRNA gene target, and real-time Polymerase Chain Reaction for the IS711 gene target diagnostic tests. Sixty-six percent of the patients were men and 34% women with 12–86 years old. The most common age group was 25–45 years. The most common clinical symptom was fever (38%), and 51.5% of the patients had a history of livestock contact. Brucella melitensis was detected in 25 of the 44 cultured samples through culture (56.81% and 82.5% specificity). All the isolated species were Brucella melitensis. A positive Wright test was detected in 33 serum samples (75% sensitivity, 89.63% specificity), a positive 2-mercaptoethanol test was detected with 68.96% sensitivity, 88.45% specificity, and an Enzyme Linked Immuno Sorbent Assay was detected with 78% sensitivity, 91.18% specificity. Polymerase Chain Reaction targeting the 16 S rRNA gene identified 32 positive samples (72.72% sensitivity, 90.9% specificity). Real-time Polymerase Chain Reaction targeting the IS711 gene revealed 34 positive samples and the highest diagnostic value, with 77.2% sensitivity and 93% specificity. The study revealed that compared with bacterial culture and serology techniques, IS711 real-time PCR is the most sensitive test. Also, selection of diagnostic tests is dependent on the acute, subacute or chronic forms of brucellosis.