Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1332 page)

   
Candida
species are common contaminants and should not routinely be identified to species level.

Suggested Readings

Carroll KC. Laboratory diagnosis of lower respiratory tract infections: controversy and conundrums.
J Clin Microbiol.
2002;40:3115–3120.

Koenig SM, Truwit JD. Ventilator-associated pneumonia: diagnosis, treatment, and prevention.
Clin Microbiol Rev.
2006;19:637–657.

BRUCELLA
CULTURE (RULE OUT)

   Definition

   Human infection may be caused by several species of the genus
Brucella
. These organisms are fastidious, slow-growing gram-negative bacilli capable of producing severe localized and systemic infection. Infections have typically been acquired by zoonotic transmission, primarily related to livestock and dairy industries. There is great concern regarding the use of this organism for a bioterror-related attack. The organism is easily transmissible, so it is critical that the laboratory be informed whenever brucellosis is suspected.

   Use

   This culture is used to isolate
Brucella
species from clinical specimens. Because of the risk of laboratory-acquired infection and because isolation of
Brucella
species may represent a sentinel event in a bioterror attack, most clinical microbiology laboratories limit the workup of suspected isolates to simple tests to rule out suspicious colonies, referring isolates that fail to “rule out” to their local public health laboratory for identification and further characterization. Final results for testing, therefore, may be delayed compared to common bacterial isolates.

   
Method:
Specimens are inoculated onto a blood agar (such as
Brucella
blood agar), chocolate agar, and Thayer-Martin agar (if contamination with endogenous flora is suspected). Specimens for
Brucella
are also inoculated onto MacConkey agar.

   
Turnaround time:
Isolation and preliminary identification for routine cultures are usually available in 3–7 days. Additional time is required for transfer to the local public health laboratory, confirmation of identification, and further testing.

   Special Collection and Transport Instructions

   The organisms primarily infect the reticuloendothelial system, so bone marrow and blood are the specimens of choice for patient evaluation. Specimens from other infected tissue or sites should also be submitted for culture. Serologic testing is recommended for diagnosis in patients with suspected brucellosis.

   Interpretation

   
Expected results:
Negative.

   
Positive:
Isolation of
Brucella
in culture is diagnostic for brucellosis.