Can a perirectal strep (Group A beta-hemolytic streptococcal infection) test be performed using the same swabbing method as a streptococcal pharyngitis (strep throat) test?

Perirectal Strep Testing Technique

Perirectal strep swabs should be performed using the same technique as throat swabs, focusing on proper sampling of the perirectal area rather than touching other areas of the perineum or rectum. 1

Proper Swabbing Technique for Strep Testing

The technique for obtaining a perirectal swab for Group A beta-hemolytic streptococcal (GAS) testing is similar to the established technique for throat swabs:

• Sampling location: The swab should be obtained from the perirectal area, focusing on the area immediately surrounding the anus 1
• Avoid contamination: Just as with throat swabs where other areas of the mouth should not be touched, avoid touching other areas of the perineum that could contaminate the sample 2
• Proper handling: After collection, the swab should be processed promptly using the same methods as for throat swabs 2

Testing Methods for Perirectal Strep

The same testing methods used for throat swabs can be applied to perirectal swabs:

• Culture method: The swab can be plated on sheep blood agar and incubated at 35°C-37°C for 18-24 hours, with potential additional incubation at room temperature for another 24 hours 2
• Rapid Antigen Detection Tests (RADTs): These can be used with perirectal swabs just as they are with throat swabs, providing quick results with high specificity (approximately 95%) 2

Clinical Relevance of Perirectal GAS Testing

Perirectal GAS testing is particularly important in certain clinical scenarios:

• Perianal cellulitis: GAS can cause perianal cellulitis, which may present as chronic diaper dermatitis, perirectal fissures, painful defecation, or fecal hoarding behavior 3
• Guttate psoriasis: In children with guttate psoriasis, perirectal sites should be cultured for GAS in addition to pharyngeal sites 3
• Recurrent infections: In families with multiple recurrent GAS infections, perirectal testing may be warranted 4

Potential Pitfalls and Considerations

• False negatives: As with throat swabs, false-negative results may occur if the patient has received antibiotics shortly before the swab is obtained 2
• Proper technique importance: Improper swabbing technique can reduce test sensitivity 4
• Carrier status: A positive test may indicate colonization rather than active infection, requiring clinical correlation 4

Treatment Implications

• If perirectal GAS is detected and deemed clinically significant:
  • Standard treatment with appropriate antibiotics (penicillin, amoxicillin) for 10 days is recommended 2
  • For carriers or recurrent cases, alternative regimens like clindamycin, amoxicillin-clavulanate, or penicillin plus rifampin may be more effective 4

The evidence from perirectal swabbing for vancomycin-resistant enterococci demonstrates that perirectal swabs are equally sensitive to rectal swabs 1, suggesting that the same principles would apply to GAS testing, allowing for the use of the same laboratory methods and interpretation guidelines as used for throat swabs.