Interpreting Abnormal Throat Culture Results: Pathogens and Significance

Throat culture identifies bacterial pathogens causing pharyngitis. Interpretation requires clinical correlation (symptoms, Centor criteria, patient age).

Significant Pathogens (Require Treatment)

• Group A β-hemolytic Streptococcus (GAS): Primary target. Treat if symptomatic (sore throat, fever, adenopathy, no cough) to prevent rheumatic fever.
• Neisseria gonorrhoeae: Sexually transmitted; pharyngitis often asymptomatic. Requires ceftriaxone + azithromycin.
• Neisseria meningitidis: Carrier state common; treat if symptomatic or outbreak.
• Corynebacterium diphtheriae: Rare; requires antitoxin + antibiotics. Public health emergency.
• Staphylococcus aureus: Treat if purulent exudate, immunocompromised, or post-viral superinfection suspected.

Organisms Requiring ≥10⁵ CFU/mL for Significance (Adults)

• Streptococcus pneumoniae
• Haemophilus influenzae
• Moraxella catarrhalis

These are common colonizers; high counts with symptoms suggest pathogenic role. Lower thresholds may apply for children.

Normal Flora (No Treatment)

Viridans streptococci, Neisseria spp. (non-gonococcal/meningitidis), Corynebacterium spp. (non-diphtheriae), anaerobes, Candida (unless immunosuppressed).

Clinical Pearl

Rapid antigen detection test (RADT) for GAS is specific but less sensitive than culture. Negative RADT in children should be backed up by culture. Treat based on combined clinical + lab assessment.