Episode 225: Group A Strep

Show Notes

Background

• Group A strep = Streptococcus pyogenes — gram-positive organism that colonizes the pharynx, but also the perianal and genital mucosa (worth remembering when the source isn’t the throat).
• Extremely common. The episode cites an estimated ~289 million cases/yr of strep pharyngitis in children 5–14 (NIH). For a U.S.-specific, verifiable anchor: the CDC estimates strep throat drives ~5.2 million outpatient visits/yr in people <65.
• No true beta-lactam resistance. GAS remains uniformly susceptible to penicillin and amoxicillin. Note this is not true for macrolides/clindamycin — roughly 1 in 3 invasive isolates are now erythromycin/clindamycin resistant.

Pathophysiology — the throughline

• Exotoxins (superantigens) tie the whole spectrum together — they drive scarlet fever, streptococcal toxic shock syndrome (STSS), and are implicated in the Kawasaki overlap discussed below.
• The organism is the same from a sore throat to a life-threat; what changes is host response and toxin burden.

Clinical Presentation

• Core findings: tonsillar inflammation/exudate, tender anterior cervical lymphadenopathy, fever.
• Classic strep tells to hunt for:
  • Palatal petechiae
  • Strawberry tongue
  • Perioral pallor
• Scarlet fever — fine, sandpapery rash, typically starts on the trunk and spreads outward; later desquamation of the fingers and toes.
• Extrapharyngeal clues: kids commonly present with abdominal pain or headache even when the throat looks unimpressive. Low threshold to test with fever + abd pain or fever + headache.

Diagnosis / Workup

Centor / Modified (McIsaac) Score

• Centor Score (Modified/McIsaac) — MDCalc
• One point each: fever, tonsillar exudates, tender anterior cervical lymphadenopathy, absence of cough. The Modified (McIsaac) version adds age.
• Developed and validated in adults (≥16). It is not reliable in young children — don’t lean on it in peds the way you would in an adult.
• For reference, McIsaac culture-positive probabilities: ~2.5% (0 criteria), 6.5% (1), 15% (2), 32% (3), 56% (4).

Testing

• Rapid PCR — high sensitivity and specificity; increasingly the front-line test.
• Rapid antigen detection test (RADT) — highly specific but less sensitive. Per IDSA, a negative RADT in a child/adolescent should be backed up with a throat culture (culture is the more sensitive gold standard). Backup culture is not required in adults.

Who not to test

• Generally don’t test/treat children <3 — acute rheumatic fever is rare in this group.
• Exception: the symptomatic young child with a close contact recently diagnosed with strep.

Management

• First-line: amoxicillin 50 mg/kg once daily, max 1 g/dose. GAS stays beta-lactam susceptible (penicillin and amoxicillin remain treatments of choice per IDSA 2012).
• IM penicillin G / benzathine (bicillin) for kids who can’t tolerate oral meds — one shot, done.
• Return to school: after one full day of treatment (~12–24 h), provided afebrile and feeling well.
• Contact prophylaxis:
  • Pharyngitis — routine prophylaxis of asymptomatic contacts is not standard; consider it for households with recurrent infection or a history of rheumatic fever.
  • Invasive GAS — more aggressive. Prophylaxis is recommended for household contacts who are immunosuppressed, pregnant, post-recent-surgery, or have an open wound (CDC).

The Bounce-Back / Treatment Failure

The kid who finishes amox and is back a week later. Sort into three buckets:

1. Chronic carrier — GAS carriage in children runs 2–20%. Carriers test positive but are asymptomatic, with low risk of transmission or complications. Don’t chase them.
2. New infection.
3. True treatment failure → ask why:
   • The shield effect — the throat is co-colonized with beta-lactamase producers (Staph aureus, H. influenzae, Moraxella) that degrade amoxicillin before it can act, effectively shielding the GAS.
   • This is NOT true resistance — the strep is still beta-lactam susceptible; the neighbors are the problem.
   • Fix: switch to a beta-lactamase–stable agent — amoxicillin-clavulanate or a first-generation cephalosporin.

Complications

• Suppurative: peritonsillar abscess, sinusitis, meningitis, bacteremia.
• Non-suppurative:
  • Acute rheumatic fever — typically 1–5 wks post-infection; Jones criteria (AHA 2015 revision · ACC summary · CDC).
  • Post-infectious glomerulonephritis (PIGN) — several weeks out; hematuria / “Coca-Cola” urine. Note strep impetigo can also seed PIGN.
• The pearl: we treat strep to prevent rheumatic fever — but treatment does NOT prevent PIGN.

Invasive Group A Strep (iGAS)

Why it’s on the radar

• Rates have been climbing since 2014, and preliminary 2023 data hit a 20-year high (CDC). A CDC/ABCs analysis flagged a roughly 3-fold pediatric increase in Colorado/Minnesota in late 2022 (MMWR).
• Keep it in mind when a child isn’t following the typical strep course or just looks sicker than expected.

The spectrum

• STSS, necrotizing fasciitis, meningitis, bacteremia, peritonitis.
• Increasingly common and worth highlighting: bone and joint disease — septic arthritis, osteomyelitis — often traveling with pyomyositis.

The trap — nonspecific early presentation

• Symptoms are often nonspecific: fever, “not acting like themselves,” localized pain.
• Septic joint/osteo may show a limp or focal pain — but not always.
• When your gut fires, cast a wide net.

Workup

• Blood cultures, CBC, chemistries, CRP, ESR.
• Imaging — tailor to the suspected site:
  • Suspected joint → start with X-ray + ultrasound.
  • Worried about osteomyelitis or pyomyositis → MRI (the recommended modality for pyomyositis per IDSA SSTI).

Management

• Broad-spectrum: vancomycin + piperacillin-tazobactam (concordant with IDSA SSTI).
• In shock / STSS: ADD clindamycin or linezolid for toxin suppression — this is on top of vanc/zosyn, not a coverage swap. (IDSA: penicillin plus clindamycin for documented GAS necrotizing infection; consider IVIG in STSS.)

The Kawasaki overlap

• Meaningful overlap between iGAS and Kawasaki disease.
• Proposed mechanism: strep superantigens activate a shared inflammatory (T-cell) pathway that may contribute to KD; some data suggest kids with iGAS may be at higher risk of developing Kawasaki.
• Get rheumatology involved early — they’ll want those inflammatory markers and can help sort KD from mimics.

Take-Home Points

1. Adult tools don’t translate to peds. Centor was built for ≥16 and is unreliable in young kids — diagnose on exam, the eponyms, and testing. Low threshold to swab the febrile kid with abdominal pain or headache.
2. The bounce-back is a triage problem — carrier (2–20%) vs. new infection vs. true failure. True failure is usually the shield effect (beta-lactamase co-colonizers, not resistance) → switch to amox-clav or a first-gen cephalosporin.
3. Treatment prevents rheumatic fever, NOT PIGN — and impetigo can cause PIGN too.
4. iGAS is rising and hides behind nonspecific symptoms. When your gut fires, work it up broadly and escalate to MRI for osteo/pyomyositis. Treat with vanc + pip-tazo, and in shock add clindamycin/linezolid for toxin suppression. Keep Kawasaki in the differential and call rheum early.

Links & References

Calculators

• Centor Score (Modified/McIsaac) for Strep Pharyngitis — MDCalc

Guidelines

• Shulman ST, et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update. IDSA / Clin Infect Dis. 2012;55(10):e86–e102. — IDSA · Full text
• Stevens DL, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update. IDSA / Clin Infect Dis. 2014;59(2):e10–e52. (necrotizing infection, STSS, clindamycin adjunct, MRI for pyomyositis) — IDSA · Full text
• Gewitz MH, et al. Revision of the Jones Criteria for the Diagnosis of Acute Rheumatic Fever in the Era of Doppler Echocardiography. AHA / Circulation. 2015;131:1806–1818. — Circulation · ACC “10 Points to Remember”

CDC

• Group A Strep Disease Surveillance and Trends (invasive disease rising since 2014; 2023 20-year high)
• MMWR — Increase in Pediatric Invasive Group A Streptococcus Infections, Colorado and Minnesota, Oct–Dec 2022
• Diagnosing Acute Rheumatic Fever (clinician guidance)