Test Catalog

Test ID: CGAS    
Group A Streptococcus (Streptococcus pyogenes) Culture, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of perianal cellulitis


Screening patients and health care workers for Streptococcus pyogenes for the purpose of investigating possible nosocomial transmission

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

When this test is ordered, the reflex tests may be performed at an additional charge.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Streptococcus pyogenes (group A streptococcus) is a common cause of pharyngitis and skin and soft tissue infection. In children, S pyogenes can cause perianal infection. The classic presentation is a well-demarcated rash around the anus with itching, rectal pain, and, occasionally, blood-streaked stools. Untreated, painful defecation, toilet avoidance, and constipation may persist for months, until effective treatment is administered. Anal fissures may ensue. A swab of the affected area may be submitted for S pyogenes culture to confirm the diagnosis.


Health care workers may transmit S pyogenes to their patients (eg, in the postsurgical setting) leading to outbreaks of invasive disease. Screening of health care workers or other patients for S pyogenes may be requested by Infection Prevention and Control as part of an investigation of a potential nosocomial case (or cases). Isolates may be typed to assess strain relatedness.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Interpretation Provides information to assist in interpretation of the test results

Positive cultures are reported out as Streptococcus pyogenes.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Spellerberg B, Brandt C, Sendi P: Streptococcus. In Manual of Clinical Microbiology. 12th edition. Edited by KC Carroll, MA Pfaller. Washington DC, ASM Press 2019, pp 399-417

2. Cohen R, Levy C, Bonacorsi S, et al: Diagnostic Accuracy of Clinical Symptoms and Rapid Diagnostic Test in Group A Streptococcal Perianal Infections in Children. Clin Infect Dis 2015 Jan 15;60:267-270