Group A Streptococcal Disease

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

Indications for Testing

Sore throat, fever, and lymphadenopathy

Laboratory Testing

  • Consider Centor score when testing for group A strep in patient with sore throat
Modified Centor Criteria for Management of Sore Throat
Criteria Points

Absence of cough

1

Swollen and tender anterior cervical nodes

1

Temperature >100.4ºF (38ºC)

1

Tonsillar exudates or swelling

1

Age

 

3-14 years

1

15-44 years

0

≥45 years

-1

Cumulative Score Suggested Management

≤0 

No testing

Risk <10%
Test if high suspicion or recent contact

2-3 

Rapid testing or throat culture

≥4 

Treatment without testing

Recommended by Centers for Disease Control (CDC), American College of Physicians (ACP), and American Academy of Family Physicians (AAFP)

Not recommended by Infectious Diseases Society of America (IDSA) or American Heart Association (AHA) – approach results in unnecessary prescribing of antibiotics

  • 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

Background

Epidemiology

  • 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

Organism

  • 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

ARUP Laboratory Tests

Gold standard for confirming group A streptococcal infection

Order when rapid testing is negative and suspicion of streptococcus is moderately high

Confirm current or recent group A streptococcal infection in patients suspected of having a nonsuppurative complication such as acute glomerulonephritis (AGN) or acute rheumatic fever (ARF)

DNase-B and antistreptolysin O (ASO) antibody tests are generally ordered concurrently

Preferred test for rheumatic chorea since it remains elevated longer

Confirm a prior infection with group A streptococcus in patients suspected of having a nonsuppurative complication such as AGN or ARF

DNase-B and ASO antibody tests are generally ordered concurrently

Related Test

Medical Experts

Contributor

Delgado

Julio Delgado, MD, MS
Executive Vice President, ARUP Laboratories
Division Chief of Clinical Pathology, University of Utah and ARUP Laboratories
Professor of Clinical Pathology, University of Utah
Medical Director, Protein Immunology and Immunologic Flow Laboratories, ARUP Laboratories
Contributor

Fisher

Mark A. Fisher, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Bacteriology, Special Microbiology, and Antimicrobial Susceptibility Testing, ARUP Laboratories

References

Additional Resources
Resources from the ARUP Institute for Clinical and Experimental Pathology®