Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (468 page)

Antigen detection
(for detection of Hib from CSF, serum, or urine): Use of antigen detection is not recommended, having been shown to rarely contribute to the clinical management of patients.

HELICOBACTER PYLORI
INFECTION

   Definition

Helicobacter pylori
is a fastidious, curved GNB.
Helicobacter pylori
infection shows a global distribution.

Most infections are transmitted by the fecal–oral route.

   Who Should Be Suspected?

Helicobacter pylori
is the cause of most gastric and duodenal ulcers through disruption of the protective mucous layer. This organism is epidemiologically linked to gastric adenocarcinoma and lymphoma.

   Laboratory Findings

Helicobacter pylori
may be diagnosed by several invasive or noninvasive means:

   
Histologic examination of gastric mucosa
: Organisms stain poorly with H&E but may be demonstrated with Giemsa or silver staining.

   
Culture of gastric mucosa
: Special culture techniques are required for isolation. The organism is microaerophilic and capnophilic and yields growth within 5 days on enriched media.

   
Urease activity
(direct tissue or breath test): Strongly positive.

   
Specific antigen
: A commercially available assay for detection of
H. pylori
antigen in feces shows a sensitivity of approximately 90% and specificity of approximately 95% for detection of active infection.
Helicobacter pylori
antigen may be useful for monitoring response to therapy.

   
Serology
:
Helicobacter pylori
antibody IgG is typically measured. Positive response is predictive of active infection in patient populations where the prevalence of active infection is not high. Antibody levels may remain persistently positive for a period after successful therapy, so serology may have a limited role in early test of cure.

KLEBSIELLA PNEUMONIAE
INFECTION

   Definition

Klebsiella pneumoniae
is a nonfastidious, glucose-fermenting GNB.
Klebsiella pneumoniae
is widely distributed in nature as well as the normal fecal flora of humans. It is a common isolate in the clinical laboratory, often associated with nosocomial infection or infection of immunocompromised hosts.

   Who Should Be Suspected?

Klebsiella pneumoniae
is associated with severe pneumonia, especially in alcoholics. The pneumonia results in necrosis and hemorrhage; mucoid, “currant jelly” sputum is classic. Bacteremia is seen in a significant number of cases.
Klebsiella pneumoniae
is also associated with primary or hospital-acquired UTI, nosocomial bloodstream, ventilator-associated, or other extraintestinal infection.
Klebsiella pneumoniae
isolates are of particular importance in hospital-acquired infections because of their intrinsic and acquired resistance to antimicrobial agents.

   Laboratory Findings