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Bacteriology, Virology, Mycology, and Parasitology

Causes of Error in Microbiology

False Positive mycology, parasitology	False Negative
Permissive site cultured (normal flora vs pathogen) Sample contamination (eg, Blood culture, CSF) Lab contaminant (eg, PCR) Bacteriology, virology, Lab error ( QC, interpretation) Wrong test ( eg, ToRCH) Old, unrelated infection	Wrong test Insensitive test (eg, CSF - encepha litis) Inadequate sample ( eg, Blood cul ture) Lab error bacteriology, virology

Pathogens vs. Normal Flora?

Site	Organisms
Nose	s. aureus (30-50%). S. pneumoniae (40-60%), H. influenzae (30-50%), N. meningitidis (20%), CMV, adenovirus
Throat	Same as above, Gp A streptococcus (20%)
Skin	S. aureus (5%), Acinetobacter, Coagulase negative Staphylococcus
Colon	E. coil, Poliovirus (vaccine), Adenovirus
Vagina	Gp B Streptococcus (30% adults)