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
1	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

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

ARUP Lab Tests

Gold standard for confirming group A streptococcal infection

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

0060126

Streptococcus (Group A) Culture 0060126

Method

Culture/Identification

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

0050220

DNase-B Antibody 0050220

Method

Quantitative Nephelometry

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

0050095

Streptolysin O Antibody (ASO) 0050095

Method

Quantitative Nephelometry