Brucella Species


Indications for Testing

  • High level of suspicion based on occupation, activities, or travel history

Laboratory Testing

  • CDC Brucellosis testing and diagnosis information
  • Initial testing
    • CBC, C-reactive protein (CRP), liver function
    • Serology – primary method of diagnosis
    • Agglutination testing – detects IgG, IgM, IgA antibodies
      • Fourfold rise in titer considered diagnostic
    • IgG and IgM by ELISA – not preferred; less sensitive than agglutination 
    • Febrile antibodies (febrile agglutinins) testing – not specific for Brucella
  • Gold standard – culture of tissue, blood, or fluids
    • Variable yield
      • 40-90% in acute cases
      • 5-20% in chronic cases
    • May require several weeks because organism is very slow growing and difficult to culture

Differential Diagnosis

Clinical Background

Brucellosis (also called undulant fever, Malta fever, Mediterranean fever) is a major bacterial zoonosis involving many mammals, including domestic cows (Brucella abortus), pigs (B. suis), goats/sheep (B. melitensis), and dogs (B. canis). The disease is also found in wild ruminant mammals such as deer, elk, and moose.


  • Incidence – 1/100,000 in U.S.
    • Most common zoonosis worldwide but relatively rare in North America and western Europe
    • Endemic in the Mediterranean, Middle East, Mongolia, Russia, Mexico, and Latin America
  • Transmission
    • Most common route is from eating or drinking infected, unpasteurized dairy products (eg, soft cheeses)
    • Inhalation (primarily from occupational exposure) and via skin wounds and abrasions
    • Vertical transmission via breast feeding


  • Brucella spp (gram-negative coccobacilli)
  • Facultative intracellular pathogens
  • Human infections are caused most frequently by B. melitensis, B. suis and B. abortus; rare infections are caused by B. canis
    • Sheep and goats are the most common reservoir

Risk Factors

  • Occupational or recreational exposure to animals
    • >70% of reported cases occur in the meat-processing and livestock industries
    • Brucella spp are able to penetrate imperceptible cuts or abrasions in the skin, leading to infections from handling infected animals
    • Among laboratory workers preparing cultures for bacterial agents, Brucella presents a higher risk of infection than other organisms

Clinical Presentation

  • Brucellosis in humans has variable incubation time, insidious or abrupt onset, and no pathognomonic symptoms or signs
  • Flu-like symptoms usually appear 1-3 weeks after exposure; during incubation (2-8 weeks), organism resides in the lymph nodes
    • Constitutional (~75% of cases) – fever, chills, headache, weakness
    • Osteoarticular (~22% of cases) – sacroiliitis, spondylitis, osteomyelitis
    • Gastrointestinal (30% of cases) – hepatomegaly (granulomatous hepatitis), splenomegaly
    • Genitourinary (5% of cases)– orchiepididymitis, glomerulonephritis, renal abscesses
    • Neurologic (6% of cases) – peripheral neuropathy, chorea, meningitis/encephalitis
    • Mucocutaneous – purpura, maculopapular lesions, Stevens-Johnson syndrome
    • Pulmonary – pneumonia, pleural effusions
    • Cardiovascular (2% of cases)– endocarditis; aortic valve most common
  • Untreated, the disease tends to become chronic and persist for years
    • Chronic symptoms may also occur up to 1 year from onset of illness and include recurrent fever, arthritis, and fatigue
  • Rarely fatal but can be severely debilitating
    • Mortality low (<1%) and almost exclusively from cardiac complications


  • Control of disease in domestic livestock
  • Avoidance of unpasteurized dairy products, including soft cheeses (especially goat cheese)

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Order to differentiate bacterial from viral etiology

C-Reactive Protein 0050180
Method: Quantitative Immunoturbidimetry

Preferred test to use as indicator of endocarditis in conjunction with clinical presentation

Hepatic Function Panel 0020416
Method: Quantitative Enzymatic/Quantitative Spectrophotometry

Test for presence of hepatitis

Panel includes albumin, alkaline phosphatase, aspartate aminotransferase, bilirubin direct, protein total, bilirubin total

Brucella Culture 0060159
Method: Culture/Identification

Gold standard for detection of Brucella in blood (optimum), CSF, body fluids, and abscesses

Time intensive

Because isolation of organism is difficult, serologic tests are generally used for diagnosis

Brucella Antibody (Total) by Agglutination 0050135
Method: Semi-Quantitative Agglutination

Diagnose brucellosis in serum samples from patients with congruent clinical history

Cross-reactions may occur between Brucella and Francisella tularensis antigens and antisera; parallel tests should be run with these antigens

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Sedimentation Rate, Westergren (ESR) 0040325
Method: Visual Identification

Determine if elevated as an indicator of endocarditis

Organism Identification by 16S rDNA Sequencing 0060720
Method: 16S rDNA Sequencing
Aerobic Organism Identification 0060115
Method: Identification. Methods may include biochemical, mass spectrometry, or sequencing.

Include warning if organism suspected to be dangerous pathogen (eg, Salmonella, Shigella, Neisseria meningitides)

For suspected agents of bioterrorism, notify state department of health and refer isolates to state laboratory for identification

Susceptibilities on agents of bioterrorism are not performed at ARUP

Febrile Antibodies Identification Panel 2010805
Method: Semi-Quantitative Agglutination/Semi-Quantitative Indirect Fluorescent Antibody/Qualitative Immunoblot

Includes Brucella Antibody (Total) by Agglutination; Rickettsia rickettsii Antibody, IgM; Rickettsia rickettsii antibody, IgG; Rickettsia typhi Antibody, IgG by IFA; Rickettsia typhi Antibody, IgM by IFA, and Salmonella typhi and paratyphi Antibodies