What are the diagnostic criteria for Brucellosis (Brucella infection)?

From the Guidelines

Diagnosing brucellosis requires a combination of clinical evaluation, laboratory tests, and imaging studies, with bone marrow cultures being the most sensitive method, yielding positivity rates of up to 90% 1. To diagnose brucellosis, the following steps can be taken:

• Clinical evaluation: considering epidemiological factors such as exposure to animals, consumption of unpasteurized dairy, and clinical presentation including fever, sweats, fatigue, and joint pain.
• Laboratory tests:
  • Blood cultures, which can isolate Brucella bacteria, though this may take 2-3 weeks and has variable sensitivity (15-70%) 1.
  • Serological tests, including the Rose Bengal test for screening and the standard tube agglutination test (SAT) with titers ≥1:160 considered significant in endemic areas.
  • ELISA tests, which offer higher sensitivity and specificity.
  • PCR testing, which provides rapid results with high sensitivity, especially in early infection or after antibiotic use.
• Imaging studies:
  • Ultrasound, CT, or MRI to help identify organ involvement, such as osteoarticular disease, hepatomegaly, and splenomegaly 1.
  • Spine MRI, which is recommended in patients with suspected native vertebral osteomyelitis (NVO) 1. It is essential to maintain a high index of suspicion in endemic regions or with relevant exposure history, as symptoms can mimic many other conditions, potentially leading to delayed diagnosis. The most recent and highest quality study 1 recommends obtaining bacterial blood cultures, baseline ESR and CRP, and a spine MRI in patients with suspected NVO, and also suggests obtaining blood cultures and serologic tests for Brucella species in patients with subacute cases of NVO residing in endemic areas for brucellosis.

From the Research

Diagnosis of Brucellosis

To diagnose brucellosis, several methods can be employed, including:

• Culture: considered the "gold standard" in the laboratory diagnosis of brucellosis due to its clinical and epidemiological relevance 2, 3
• Serological tests: indirect diagnosis by detecting antibodies against Brucella spp., despite limitations such as lack of common interpretative criteria and suboptimal specificity 4, 2, 3
• Molecular PCR-based methods: direct rapid diagnosis with high sensitivity and specificity, but requiring attention to interpretation of results 2, 3

Laboratory Techniques

Various laboratory techniques are used for the diagnosis of brucellosis, including:

• Blood culturing: although time-consuming and not always reliable, can be used for direct detection of Brucella spp. 4
• Serum agglutination test: a conventional serological test, but lacks sensitivity and specificity 4
• Enzyme-linked immunosorbent assays (ELISA): can be used for screening and confirmation of brucellosis in one step 4
• Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP): molecular techniques used to differentiate species and strains within the genus Brucella 4

Interpretation of Results

Interpretation of results from diagnostic tests for brucellosis requires attention, as:

• Positive molecular test results may not necessarily indicate an active infection, but rather a low bacterial inoculum, DNA from dead bacteria, or a patient that has recovered 2, 3
• Serological test results may be difficult to interpret in individuals repeatedly exposed to Brucella organisms 2