Group A strep pharyngitis and rapid strep testing
Group A Streptococcus (GAS, Streptococcus pyogenes) is a gram-positive coccus that grows in chains. It is the most common cause of bacterial pharyngitis in children and adolescents that benefits from antibiotics, and it accounts for 15–30% of pharyngitis in children aged 5–15 years. GAS peaks in winter and early spring.
Department note: rapid strep antigen testing (RADT) is now available in the SIUH EDs (North and PB) to speed diagnosis and treatment, especially for pediatric patients.
Clinical presentation
History
Abrupt onset of fever, headache, abdominal pain, nausea and vomiting, and sore throat.
Decreased oral intake.
Symptoms usually resolve on their own in 3–5 days.
Exam
Exudative tonsillopharyngitis
Enlarged, tender anterior cervical lymph nodes
Palatal petechiae
Inflamed uvula
Scarlatiniform rash
Absence of viral features: rhinorrhea, conjunctivitis, cough, anterior stomatitis, discrete ulcerative lesions or vesicles, diarrhea.
Complications
| Non-suppurative | Suppurative |
|---|---|
| Acute rheumatic fever | Necrotizing fasciitis |
| Post-streptococcal glomerulonephritis | Bacteremia |
| PANDAS (pediatric autoimmune neuropsychiatric disorder associated with streptococci) | Peritonsillar cellulitis or abscess |
| Retropharyngeal cellulitis or abscess | |
| Otitis media; sinusitis |
Who to test: IDSA guidance
The Infectious Diseases Society of America guideline on GAS pharyngitis (Shulman 2012, PMID 22965026) is the key reference for strep testing. IDSA updated this guidance in 2025 (Linder 2025), recommending a clinical scoring system to decide who should be tested.
Clinical features alone cannot diagnose strep throat, because viral infections can mimic it. Confirm with a rapid antigen detection test (RADT) and/or throat culture before treating, rather than treating on symptoms alone.
Do not test when viral features are obvious (for example, cough, rhinorrhea, hoarseness, oral ulcers), and avoid empiric antibiotics without confirmation.
Validated clinical decision tools, such as the Centor or McIsaac score, can help identify who to test.
Children and adolescents
RADT positive: no culture needed. The test is highly specific.
RADT negative: send a backup throat culture so GAS is not missed.
Under 3 years: routine testing is not recommended, because classic GAS pharyngitis and acute rheumatic fever are uncommon at this age. Consider testing if a household contact has documented GAS. "Less than 3, let it be!" (PEM Morsels)
Adults
RADT positive confirms GAS.
RADT negative usually does not need a backup culture, because GAS and its complications (acute rheumatic fever) are much less common in adults.
Molecular testing (NAAT/PCR)
Substantially more sensitive than traditional RADTs, with results in minutes to hours. Because it is so sensitive, a negative NAAT/PCR generally does not need a backup culture.
The test at SIUH
Henry Schein One Step+ Strep A Antigen Dipstick Test: a lateral-flow immunoassay. Reported sensitivity is 97% and specificity 95%, with a runtime of about 5–6 minutes.
The manufacturer requires culture confirmation of negative rapid tests, so two swabs are needed per patient.
At SIUH we use the RADT (rapid strep), not NAAT/PCR.
Treatment
Penicillin and amoxicillin are first line.
Children: oral penicillin V or amoxicillin for 10 days, which improves eradication of GAS from the oropharynx.
Adults: oral penicillin V 500 mg twice or three times daily for 10 days, or amoxicillin.
Penicillin allergy: consider a cephalosporin, clindamycin, or a macrolide.
Summary
Child or adolescent with suspected strep throat:
Obvious viral symptoms → do not test.
If testing is indicated:
RADT positive → treat.
RADT negative → backup culture (or follow the institution's molecular-testing protocol).
NAAT/PCR positive → treat.
NAAT/PCR negative → generally no culture needed.
Adults:
Test only when clinical features suggest GAS.
A negative RADT generally does not need culture confirmation.
Molecular testing is a highly sensitive alternative.
Clinical pearls
Antistreptococcal antibody titers (ASO, anti-DNase B) indicate past infection, not current infection.
About 20% of children are GAS carriers. Indiscriminate testing will find strep that is not causing the symptoms.
Less than 3, let it be.
References and resources
Shulman ST, Bisno AL, Clegg HW, et al. 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–e102. PMID: 22965026
Linder JA, Watson ME, Wessels MR, et al. 2025 clinical practice guideline update by the Infectious Diseases Society of America on group A streptococcal pharyngitis: risk assessment using clinical scoring systems in children and adults. Clin Infect Dis. 2026;82(Suppl 3):i97–i104. doi: 10.1093/cid/ciaf668
Pediatric EM Morsels. Strep pharyngitis testing in toddlers
