Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1319 page)

   Anaerobic culture may be significantly compromised by collection and transport conditions that are not strictly anaerobic or because of refrigeration during transport. Inadequate site preparation may result in false-positive cultures due to specimen contamination with endogenous flora. Contaminated cultures may also mask the recognition of slow-growing or fastidious anaerobic pathogens in the culture.

BACTERIAL ANTIGEN DETECTION

   Definition and Use

   This test in intended for the rapid initial detection of
Streptococcus pneumoniae
,
Haemophilus influenzae
type b, group B beta-hemolytic
Streptococcus
(GBS), or
Neisseria meningitidis
in CSF. The indication for this test is limited. Published reports have demonstrated limited sensitivity for the detection of patients with meningitis caused by common pathogens, and test results rarely result in changes to the management or therapy of patients. There may be some utility in patients who have been treated with antibiotics prior to CSF collection. There is some evidence that the performance for initial detection of GBS meningitis in neonates is acceptable.

   Latex particles are coated with antibodies directed against specific antigens of the pathogens noted above. Agglutination should occur if the antigen is present in CSF, as either a free antigen or intact bacterial cells. Specimens are collected and transported according to directions for CSF culture.

   
Turnaround time:
<4 hours

   Interpretation

   
Expected results:
Negative; no agglutination means that a CSF infection caused by specific pathogen is less likely. Positive agglutination for specific latex reagent: CSF infection caused by the specific pathogen is more likely.

   Limitations

   The sensitivity and specificity are too low to be recommended for routine use. Results are unlikely to change patient therapy or management.

Suggested Readings

Perkins MD, Mirrett S, Reller LB. Rapid bacterial antigen detection is not clinically useful.
J Clin Microbiol.
1995;30(06):1486–1491.

Ringelmann R, Heym B, Kniehl E. Role of immunologic tests in diagnosis of bacterial meningitis.
Antibiot Chemother.
1992;45:68–78.

BLOOD CULTURE, FUNGAL

   Definition and Use

   Fungal blood cultures are used for detection of bloodstream infection caused by fungi, especially when dimorphic species and uncommon pathogens are suspected. Identification, susceptibility, and further testing can be performed on culture isolates. The culture is indicated primarily for patients with cancer, extensive therapy with broad-spectrum antibiotics, trauma, and HIV and other immunocompromising conditions and symptoms that suggest sepsis, like fever, chills, malaise, hypotension, poor perfusion, toxicity, tachycardia, and hyperventilation. Biphasic and lysis–centrifugation methods have demonstrated improved isolation of dimorphic and filamentous fungi.