Brucellosis (Brucella spp.)

2024 Case Definition (modified by ADPH)

CSTE Position Statement Number: 24-ID-03

Clinical Presentation

Brucellosis is a zoonotic disease caused by certain bacteria in the Brucella genus categorized as brucellosis causing Brucella species (BBS). There are multiple BBS (listed with preferred animal host) known to infect humans, including but not limited to: B. abortus (cattle), B. melitensis (goats, sheep, camels), B. suis (pigs), B. canis (dogs), and B. neotomae (wood rats). Brucella abortus, B. melitensis, and B. suis cause most cases of brucellosis reported in the United States (U.S.). Although B. canis can be transmitted to humans from infected dogs, human infection is uncommon.

Persons are exposed to BBS through contact with infected animals or contaminated animal products, often unpasteurized dairy products. Contamination of skin wounds may be a route of infection for persons working in slaughterhouses, meat processing plants, or veterinary practices. Hunters may be infected through skin wounds or by ingesting the bacteria after butchering deer, elk, moose, or wild pigs. Inhalation is not a common infection route but can be a hazard for people working in laboratories where BBS are cultured. Rarely, transmission has occurred via organ transplantation, blood transfusion, sexual contact, breastfeeding, or transplacentally.

Clinical manifestations include initial symptoms such as fever, night sweats, malaise, headache, anorexia, myalgia, and arthralgias. Some symptoms may persist, including recurrent fevers, arthritis, spondylitis, orchitis/epididymitis, endocarditis, chronic fatigue, and hepatomegaly and/or splenomegaly.

Clinical Criteria

An illness characterized by acute or insidious onset of fever AND

Two or more of the following signs and symptoms:

  • Night Sweats
  • Arthralgia
  • Headache
  • Fatigue
  • Anorexia
  • Myalgia
  • Weight loss
  • Arthritis
  • Spondylitis
  • Meningitis, encephalitis, or other neurologic
    abnormalities
  • Discitis/osteomyelitis
  • Abscesses
  • Focal organ involvement (including, but not
    limited to: endocarditis, orchitis/epididymitis,
    hepatomegaly, splenomegaly)

Laboratory Criteria

Confirmatory Lab Evidence

Category 1:

Category 2:

Presumptive Laboratory Evidence

Supportive Laboratory Evidence

Case classification

Confirmed:

Probable:

Suspect:

Criteria to Distinguish a New Case of Brucellosis from Reports or Notifications which Should Not be Enumerated as a New Case for Surveillance

Public health authorities should enumerate new cases of brucellosis in the following instances:

A person should not be enumerated as a new case if previously enumerated as a case AND there is evidence the new report is due to one of the following: brucellosis relapse, chronic infection, or delayed convalescence.**

CSTE recommends the following case statuses be included in the CDC Print Criteria:

For this disease/condition, Confirmed and Probable case statuses are included in the released case count.

Classification Table: Criteria for defining a case of Brucellosis

Criterion Confirmed Probable Suspect
Clinical Criteria
Acute or insidious onset of fever N N N N
Two or more of the following:
  • Night Sweats
  • Arthralgia
  • Headache
  • Fatigue
  • Anorexia
  • Myalgia
  • Weight loss
  • Arthritis
  • Spondylitis
  • Meningitis, encephalitis, or other neurologic
    abnormalities
  • Discitis/osteomyelitis
  • Abscesses
  • Focal organ involvement (including, but not
    limited to: endocarditis, orchitis/epididymitis,
    hepatomegaly, splenomegaly)
N N N N
Laboratory Criteria*
Identification of a Brucella isolate as a brucellosis-causing Brucella species (BBS) by methods specific for BBS (i.e., PCR assay with documented specificity for BBS and/or biochemical tests and/or whole genome sequencing of Brucella isolate) S
Evidence of fourfold or greater rise in Brucella antibody titer between acute and convalescent serum specimens obtained at least 2 weeks apart** N S
Brucella total antibody titer >1:160 by standard tube agglutination (SAT) or Brucella microagglutination test in one or more serum samples obtained after onset of symptoms N S
Detection of Brucella IgG antibodies by ELISA in a sample collected at least 2 weeks after onset of symptoms S
Epidemiologic Linkage Criteria
Direct contact with body fluids or tissue from a confirmed human case of brucellosis O
Veterinary occupational exposure to Brucella vaccine (i.e., needle stick, mucous membrane exposure) O
Laboratory exposure to Brucellosis-causing Brucella species (BBS) O
Direct contact to an animal diagnosed with a Brucella infection (or their fluids), as determined by a state or federal animal health official, including potential aerosol exposure O
Shared an exposure with a confirmed human case of brucellosis N
Consumption of dairy products from a common source that were unpasteurized or of unknown pasteurization, particularly from countries lacking domestic animal health programs O
Consumption or handling of undercooked meat or carcass of an animal from a herd or of a species with a known or suspected history of Brucella O
Slaughtering, dressing, butchering, or having other direct contact with animals or animal tissues possibly infected with Brucella O
Vital Record Criteria
Death certificate lists brucellosis as a cause of death or a significant condition contributing to death S

Notes:
S = This criterion alone is SUFFICIENT to classify a case.
N = All “N” criteria in the same column are NECESSARY to classify a case.
O = At least one of these “O” (ONE OR MORE) criteria in each category (categories=clinical evidence,
laboratory evidence, and epidemiologic evidence) in the same column—in conjunction with all “N”
criteria in the same column—is required to classify a case.
*See Appendix A for additional information regarding brucellosis laboratory criteria.
 **To ensure consistency with laboratory methodologies, it is recommended that paired sera testing for the purposes
of confirmatory classification be conducted within the same laboratory.

Date Posted: