Advanced Techniques in Diagnostic Microbiology

TABLE 3.2. Application of techniques to detection of specific pathogens.
Pathogen Methods Specimen Sensitivity Specificity Comments
Bacteria
Streptococcus
group A
Streptococcus
pneumoniae
Agglutination,
rapid EIA,
OIA
Throat swab 70–90+% >95% Often performed at POC. Negatives must be evaluated
by culture.
Rapid EIA Urine 50–85% 94% Clinical role still evolving. Provides adjunct, but not
definitive, diagnostic information in patients at risk
for S. pneumoniae disease.
Legionella spp. IF Respiratory 25–75% 90%+ Requires FA microscope. Cross-reactions with some
other bacteria, especially with polyclonal reagents.
No gold standard for comparison.
EIA or IC Urine 80–99% 99% Test characteristics well-established only for L.
pneumophilia group 1.
Clostridium difficile Agglutination, rapid EIA,
ELISA, OIA
Stool 65–100% 88–100% Measured sensitivity and specificity are relative to tissue
culture cytotoxicity. Tests detecting Toxin A + B are
more sensitive than those detecting Toxin A only.
Helicobacter pylori ELISA Stool 89% 90–94% Used as an alternative to serology and urea breath
testing.
Chlamydia
trachomatis
Meningitis panel (H.
influenzae, N.
meningitidis, S.
pneumoniae,
group B
Streptococcus)
ELISA Genital 60–70% 97% Being phased out, but POC versions might be valuable
if sensitivity improves. No single-test format
available. Not useful for screening low-prevalence
populations due to poor specificity.
Agglutination CSF, urine Inadequate sensitivity/specificity for routine clinical
use. Empirical therapy given for CSF neutrophilia
covers these pathogens, until culture results available.
Positive predictive value of antigen tests is very low
in patients without CSF leukocytosis.
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