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Brucellosis is a common zoonotic disease throughout Africa, Asia, the Middle East, Mediterranean Basin, Eastern Europe, the Caribbean, Central America and South America. Approximately 100 to 140 cases are reported annually in the United States. The primary human pathogens are B. melitensis, B. abortus and B. suis.

Brucellae are small, slow-growing Gram-negative coccobacilli that typically infect livestock including goats, sheep, cattle and pigs. Most exposures occur in countries where brucellosis is endemic and unpasteurized milk or milk products are consumed. Less commonly, infections occur in farm settings after inhalation of organisms or direct contact with blood or body fluids during the slaughter of infected animals.

Incubation period ranges from weeks to months. Symptoms consist of fever, profuse sweating, fatigue, headache, weight loss and arthralgia. Lymphadenopathy, hepatomegaly, splenomegaly, cytopenia, and hepatitis are common. Relapse may occur in spite of lengthy antibiotic therapy.

Brucellosis is the most commonly reported laboratory-acquired bacterial infection, possibly because of two reasons. Brucellae can be easily aerosolized in the laboratory, leading to innhalation or ingestion and the infectious dose is very low. CDC recommends that laboratories use procedures that minimize splashes or aerosols of unidentified isolates and that culture plate sniffing should be prohibited.  Slow growing Gram-negative and Gram-variable organisms should be handled in a biological safety cabinet. Clinicians need to notify the microbiology laboratory that brucellosis is suspected so that cultures can be incubated for at least 10 days and biosafety precautions are taken to prevent laboratory exposures.

Bacterial isolation is the most reliable way to diagnose brucellosis. Brucella can be isolated from blood, bone marrow, joint fluid, CSF, abscesses and purulent discharge. More than 72 hours of growth is typically needed to detect Brucella in automated blood culture systems. 

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