Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1389 page)

   Sputum (expectorated or induced), BAL, bronchial brush, lung biopsy, or tracheal aspirate specimens are usually submitted for culture to rule out
Legionella
.

   Submission of multiple specimens is recommended to improve sensitivity of detection because shedding may be intermittent for this intracellular pathogen.

   Blood, cardiac valve, or other specimen types are occasionally submitted when extrapulmonary legionellosis is suspected. (If
Legionella
endocarditis is suspected, alert the laboratory because special processing and culture techniques are required.)

   Use

   Culture Method:

   All specimens should be inoculated onto supplemented BCYE agar, both nonselective and selective.

   Specimens may be diluted 1:10 in tryptic soy broth to prepare culture inoculum. For specimens that are likely to be heavily contaminated by endogenous flora, a 1:10 dilution of specimen in 0.2M KCl acid wash (pH = 2.2) is recommended to improve isolation of
Legionella
. The specimen is incubated at room temperature for 4 minutes, and then aliquots are inoculated onto selective and nonselective BCYE media as for unwashed specimens.

   Cultures are incubated at 35–37°C in a humidified incubator. CO
₂
supplementation (2–5%) may be used.

   
Turnaround time:
Cultures are inspected for up to 5 days after inoculation. Additional time is required after isolation for confirmation and further characterization.

   Interpretation

   
Expected results:
Negative.

   
Positive results:
Positive cultures confirm a diagnosis of legionellosis. Isolates from
Legionella
cultures must be confirmed as
Legionella
species by further testing and characterization.

   
Negative results:
Because
Legionella
may be shed intermittently, a negative culture does not rule out legionellosis.