Three types of culture may be used to diagnose respiratory tract infections: sputum, throat swabs, and nasopharyngeal swabs. At times, the purposes for which certain tests are ordered overlap.
Reference Values
The following organisms may be present in the nasopharynx of apparently healthy persons:
C. albicans
Corynebacterium spp.
Haemophilus haemolyticus, Haemophilus parainfluenzae
Staphylococci (coagulase negative)
Streptococci (alpha-hemolytic)
Streptococci (nonhemolytic)
Micrococci
Lactobacillus spp.
Veillonella spp.
Clinical Alert
Twenty percent of normal adults carry S. aureus; 10% are carriers of group A hemolytic streptococci.
A rapid strep test gives results after 10 minutes instead of 24–48 hours. It has a false-negative rate of 5% to 10%, about the same as traditional methods. It permits rapid diagnosis and treatment.
Both throat and urine cultures are done to detect cytomegalovirus (CMV).
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