What are the criteria for testing for strep throat?

Criteria for Testing for Strep Throat

Testing for Group A Streptococcal (GAS) pharyngitis should be performed using rapid antigen detection test (RADT) and/or throat culture when clinical features suggest possible streptococcal infection, but should not be done when overt viral features are present. 1

Clinical Features to Guide Testing Decisions

• Test when these features are present:

  • Sudden onset of sore throat 1
  • Age 5 to 15 years (highest risk group) 1
  • Fever 1
  • Headache 1
  • Nausea, vomiting, or abdominal pain 1
  • Tonsillopharyngeal inflammation 1
  • Patchy tonsillopharyngeal exudates 1
  • Palatal petechiae 1
  • Anterior cervical adenitis (tender nodes) 1
  • Presentation in winter or early spring 1
  • History of exposure to streptococcal pharyngitis 1
  • Scarlatiniform rash 1

• Do not test when these viral features are present:

  • Conjunctivitis 1
  • Coryza (runny nose) 1
  • Cough 1
  • Diarrhea 1
  • Hoarseness 1
  • Discrete ulcerative stomatitis 1
  • Viral exanthem 1

Testing Recommendations by Age Group

• Children <3 years old:

  • Testing is generally not recommended due to low incidence of GAS pharyngitis and rare occurrence of rheumatic fever in this age group 1
  • Exception: Consider testing if child has risk factors such as an older sibling with GAS infection 1

• Children and adolescents (3-18 years):

  • Perform RADT when clinical features suggest possible GAS pharyngitis 1
  • If RADT is negative, a backup throat culture should be performed due to higher risk of rheumatic fever in this age group 1
  • Positive RADT results are highly specific and do not require backup culture 1

• Adults:

  • Perform RADT when clinical features suggest possible GAS pharyngitis 1
  • Backup throat culture after negative RADT is generally not necessary due to lower incidence of GAS infection and extremely low risk of rheumatic fever 1
  • Physicians who wish to ensure maximal sensitivity may continue to use backup cultures 1

Testing Methods

• Rapid Antigen Detection Test (RADT):

  • Provides immediate results 2
  • High specificity (≥95%) but variable sensitivity (80-90%) 1
  • Proper swabbing technique is crucial - must swab both posterior pharyngeal wall and tonsils 2
  • Positive results are reliable and can guide immediate treatment decisions 1

• Throat Culture:

  • Gold standard for diagnosis 3
  • Results typically available in 24-48 hours 1
  • Required as backup for negative RADT in children and adolescents 1

Special Considerations

• Anti-streptococcal antibody titers are not recommended for routine diagnosis of acute pharyngitis as they reflect past rather than current infections 1

• Follow-up post-treatment testing is not routinely recommended unless special circumstances exist 1

• Testing of asymptomatic household contacts of patients with GAS pharyngitis is not routinely recommended 1

• The accuracy of testing depends significantly on proper specimen collection technique - both tonsils and posterior pharynx should be swabbed 2

Common Pitfalls to Avoid

• Treating based on clinical symptoms alone without laboratory confirmation leads to antibiotic overuse 2

• Testing patients with clear viral symptoms unnecessarily increases healthcare costs and may lead to inappropriate antibiotic use 1

• Failing to confirm negative RADT with throat culture in children and adolescents may miss 10-20% of true GAS infections 2

• Using antistreptococcal antibody titers for diagnosis of acute pharyngitis provides misleading information 1