Which site should I swab to obtain a specimen for diagnosing Group A Streptococcus infection?

Proper Swabbing Technique for Group A Streptococcus Detection

Swab both tonsils (or tonsillar fossae) and the posterior pharyngeal wall to obtain an adequate specimen for diagnosing Group A Streptococcus pharyngitis. 1

Correct Swabbing Sites

• The swab must contact the surface of both tonsils (or tonsillar fossae if tonsils have been removed) and the posterior pharyngeal wall, as these are the primary sites where Group A Streptococcus colonizes during acute pharyngitis. 1

• Avoid touching any other areas of the oropharynx or mouth before or after sampling the appropriate sites, as contamination from these areas can yield false-negative results or introduce commensal organisms that interfere with interpretation. 1

Why This Technique Matters

• The manner in which the swab is obtained has a critical impact on the yield of streptococci from throat culture, with proper technique achieving 90–95% sensitivity for detecting Group A Streptococcus. 1

• Sampling only the tonsillar surface may miss up to 30% of Group A Streptococcus infections, as research demonstrates significantly higher bacterial recovery rates from the posterior pharyngeal wall compared to tonsillar surfaces alone (67% versus 47% positive cultures). 2

• For detection of Group A beta-hemolytic streptococci specifically, sampling both tonsillar surfaces is sufficient, but including the posterior pharyngeal wall maximizes overall diagnostic yield. 2

Common Pitfalls to Avoid

• Do not swab only the posterior pharyngeal wall while avoiding the tonsils, as this incomplete technique reduces sensitivity for streptococcal detection. 1

• Do not allow the swab to touch the tongue, buccal mucosa, or uvula, as these sites are not acceptable for sampling and introduce contaminating oral flora. 1

• Avoid obtaining the specimen if the patient has recently taken antibiotics, as this can produce false-negative results even with proper swabbing technique. 1

Clinical Context

• This swabbing technique applies to both rapid antigen detection tests (RADTs) and throat cultures, as both diagnostic modalities require adequate specimen collection from the correct anatomic sites. 1

• The accuracy of RADTs depends heavily on the skill and experience of the person obtaining the throat swab, making proper technique essential for reliable results. 3