Group A Streptococcal 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

• 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

• Viral
  • Epstein-Barr virus
  • Rhinovirus
  • Adenovirus
  • Influenza virus
  • Cytomegalovirus
  • Respiratory syncytial virus
  • Enterovirus
    • Coxsackievirus
    • Echovirus
  • Herpes simplex virus
  • HIV
• Bacterial 
  • Group C or G streptococci
  • Corynebacterium diphtheriae
  • Arcanobacterium haemolyticum
  • Neisseria gonorrhoeae
  • Mycoplasma pneumoniae
  • Yersinia enterocolitica (rare)
  • Chlamydophila pneumoniae
  • Oropharyngeal tularemia
  • Epiglottis
  • Retropharyngeal abscess
• Malignant
  • Head and neck cancer – tonsillar
• Lymphadenitis
  • Bacterial
    • Atypical mycobacteria
    • Secondary to head and neck infections
  • Fungal
    • Histoplasmosis
    • Coccidiomycosis
  • Viral
  • Malignant
    • Head and neck cancer
    • Metastatic cancer

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