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BRUCELLOSIS

Microbiology

Brucellae are small, gram-negative, unencapsulated, nonsporulating, nonmotile rods or coccobacilli that can persist intracellularly. The genus Brucella includes four major clinically relevant species: B. melitensis (acquired by humans most commonly from sheep, goats, and camels), B. suis (from swine), B. abortus (from cattle or buffalo), and B. canis (from dogs).

Epidemiology

Brucellosis is transmitted via ingestion, inhalation, or mucosal or percutaneous exposure; the disease in humans is usually associated with exposure to infected animals or their products in either occupational settings (e.g., slaughterhouse work, farming) or domestic settings (e.g., consumption of contaminated foods, especially dairy products). The global prevalence of brucellosis is unknown because of difficulties in diagnosis and inadequacies in reporting systems.

Clinical Manifestations

Regardless of the specific infecting species, brucellosis often presents with one of three patterns: a febrile illness similar to but less severe than typhoid fever; fever and acute monarthritis, typically of the hip or knee, in a young child (septic arthritis); or long-lasting fever, misery, and low-back or hip pain in an older man (vertebral osteomyelitis).

  • An incubation period of 1 week to several months is followed by the development of undulating fever; sweats; increasing apathy, fatigue, and anorexia; and nonspecific symptoms such as headache, myalgias, and chills.

  • Brucella infection can cause lymphadenopathy, hepatosplenomegaly, epididymoorchitis, neurologic involvement, and focal abscess.

  • Given the persistent fever and similar symptoms, tuberculosis is the most important differential diagnosis (Table 100-1).

TABLE 100-1RADIOLOGY OF THE SPINE: DIFFERENTIATION OF BRUCELLOSIS FROM TUBERCULOSIS

Diagnosis

Laboratory personnel must be alerted to the potential diagnosis to ensure that they take precautions to prevent occupational exposure.

  • The organism is successfully cultured in 50–70% of cases. Cultures using the BACTEC systems usually become positive in 7–10 days and can be deemed negative at 3 weeks.

  • PCR analysis of blood or tissue samples is more sensitive, faster, and safer than culture.

  • Agglutination assays for IgM are positive early in infection. Single titers of ≥1:160 and ≥1:320 are diagnostic in nonendemic and endemic areas, respectively.

TREATMENT Brucellosis

  • The recommended regimen is streptomycin at a dosage of 0.75–1 g/d (or gentamicin at 5–6 mg/kg qd) for 14–21 days plus doxycycline at a dosage of 100 mg bid for 6 ...

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