Streptococcal Disease, Group A - Group A, Strep

Group A streptococci (Streptococcus pyogenes) cause a broad spectrum of disease and are the primary bacterial cause of exudative tonsillitis and pharyngitis. Rheumatic fever, a resulting complication of untreated streptococcus infection, may develop 2-4 weeks after a streptococcal throat infection. In serious cases, rheumatic fever can cause heart disease.

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

Sore throat, fever, and lymphadenopathy

Laboratory Testing

  • Consider Centor score when testing for group A strep in patient with sore throat
  • Rapid antigen detection with reflex to culture for initial negative antigen testing in children
    • Sensitivity – 70-90%
    • Specificity – >95%
  • Swabbing posterior pharynx increases sensitivity of both rapid antigen test and culture
  • Positive rapid test confirms strep infection in presence of clinical syndrome
  • Throat culture – sensitivity 90-95%
  • Occurrence of strep infection in adults is low (10%); follow-up culture of negative rapid antigen not usually indicated
  • Antibody tests (antistreptolysin O [ASO] and anti-DNase-B) – provide serologic evidence of prior and current infection in suspected poststreptococcal glomerulonephritis or rheumatic fever (Parks, 2015)
    • May be indicated for
      • Patients with suspected acute rheumatic fever and poststreptococcal glomerulonephritis in high-risk settings
        • Either titer (ASO, anti-DNase-B) may be used for glomerulonephritis antibody
        • Both antibody tests should be used to exclude rheumatic heart disease
      • Patients with suspected rheumatic fever and poststreptococcal pharyngitis in low-risk settings – negative or low ASO usually sufficient to rule out disease
    • Not useful in diagnosing acute streptococcal disease (titers rise 7-14 days after infection and peak in 2-3 weeks) – convalescent titers with rise are best evidence of antecedent streptococcal infection
  • Elevated serum ASO titers – found in about 85% of individuals with acute rheumatic fever
    • ASO and anti-DNase-B antibodies – elevated titers in 90-95% of acute rheumatic fever patients
    • Skin infections with group A streptococci
      • Often associated with a poor ASO response
      • Anti-DNase-B titers are increased after skin infection

Differential Diagnosis


  • Prevalence
    • Streptococcal pharyngitis
      • Represents 1-2% of primary care visits
      • 1 of the top 20 reported diseases
    • Rheumatic fever poststreptococcal pharyngitis – 1-2/100,000
  • Age – usually <20 years
    • Rare in children <3 years old
  • Transmission – direct contact with nasal discharge
    • Seasonally most common in winter and/or early spring


  • Streptococcus pyogenes bacteria are gram-positive cocci
  • May evoke cross-reacting immune response with human tissue leading to the postinfection sequelae of  
    • Acute rheumatic fever (including rheumatic heart disease) – associated with streptococcal pharyngitis
    • Acute glomerulonephritis – associated with both streptococcal pharyngitis and skin disease
  • Causes a range of human disease
    • Pharyngitis
    • Impetigo
    • Scarlet fever
    • Invasive infections

Risk Factors

  • Young age
  • Crowded conditions

Clinical Presentation

  • Primary symptoms – sudden onset sore throat, fever (>100.4°F), headache
  • Constitutional symptoms – nausea, vomiting, abdominal pain
  • Clinical findings – pharyngeal erythema, exudative tonsillitis, anterior cervical adenopathy, palatine petechiae
    • Presence of cough, hoarseness, pharyngeal ulcers, diarrhea, and/or conjunctivitis are more suggestive of viral pharyngitis
    • Fine papular erythematous (sandpaper) rash – scarlet fever
  • Complications
    • Peritonsillar abscess
    • Toxic shock syndrome – almost exclusively associated with soft tissue infections
    • Rheumatic fever – rheumatic heart disease
    • Poststreptococcal glomerulonephritis
    • Poststreptococcal reactive arthritis
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Streptococcus (Group A) Culture 0060126
Method: Culture/Identification

DNase-B Antibody 0050220
Method: Quantitative Nephelometry

Streptolysin O Antibody (ASO) 0050095
Method: Quantitative Nephelometry


Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, Martin JM, Van Beneden C, Infectious Diseases Society of America. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis. 2012; 55(10): e86-102. PubMed

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Group A Streptococcal (GAS) Disease. Centers for Disease Control and Prevention. Atlanta, GA [Last updated: Sep 2016; Accessed: Oct 2017]

General References

Alcaide ML, Bisno AL. Pharyngitis and epiglottitis. Infect Dis Clin North Am. 2007; 21(2): 449-69, vii. PubMed

Choby BA. Diagnosis and treatment of streptococcal pharyngitis. Am Fam Physician. 2009; 79(5): 383-90. PubMed

Clerc O, Greub G. Routine use of point-of-care tests: usefulness and application in clinical microbiology. Clin Microbiol Infect. 2010; 16(8): 1054-61. PubMed

Kalra MG, Higgins KE, Perez ED. Common questions about streptococcal pharyngitis. Am Fam Physician. 2016; 94(1): 24-31. PubMed

Kociolek LK, Shulman ST. In the clinic. Pharyngitis. Ann Intern Med. 2012; 157(5): ITC3-1 - ITC3-16. PubMed

Parks T, Smeesters PR, Curtis N, Steer AC. ASO titer or not? When to use streptococcal serology: a guide for clinicians. Eur J Clin Microbiol Infect Dis. 2015; 34(5): 845-9. PubMed

Wessels MR. Clinical practice. Streptococcal pharyngitis. N Engl J Med. 2011; 364(7): 648-55. PubMed

Zühlke LJ, Beaton A, Engel ME, Hugo-Hamman CT, Karthikeyan G, Katzenellenbogen JM, Ntusi N, Ralph AP, Saxena A, Smeesters PR, Watkins D, Zilla P, Carapetis J. Group A streptococcus, acute rheumatic fever and rheumatic heart disease: epidemiology and clinical considerations. Curr Treat Options Cardiovasc Med. 2017; 19(2): 15. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Martins TB, Augustine NH, Hill HR. Development of a multiplexed fluorescent immunoassay for the quantitation of antibody responses to group A streptococci. J Immunol Methods. 2006; 316(1-2): 97-106. PubMed

Martins TB, Hoffman JL, Augustine NH, Phansalkar AR, Fischetti VA, Zabriskie JB, Cleary PP, Musser JM, Veasy G, Hill HR. Comprehensive analysis of antibody responses to streptococcal and tissue antigens in patients with acute rheumatic fever. Int Immunol. 2008; 20(3): 445-52. PubMed

Martins TB, Veasy G, Hill HR. Antibody responses to group A streptococcal infections in acute rheumatic fever. Pediatr Infect Dis J. 2006; 25(9): 832-7. PubMed

Stockmann C, Ampofo K, Hersh AL, Blaschke AJ, Kendall BA, Korgenski K, Daly J, Hill HR, Byington CL, Pavia AT. Evolving epidemiologic characteristics of invasive group a streptococcal disease in Utah, 2002-2010. Clin Infect Dis. 2012; 55(4): 479-87. PubMed

Medical Reviewers

Content Reviewed: 
October 2017

Last Update: November 2017