Episode 225: Group A Strep

Group A strep in the pediatric ED: from strep throat to invasive disease and toxic shock.

Host:

Ellen Duncan, MD, PhD

Brian Gilberti, MD

https://media.blubrry.com/coreem/content.blubrry.com/coreem/Group_A_Strep.mp3

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Tags: Infectious Diseases, Pediatrics

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:

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.

New infection.

True treatment failure → ask why:

The shield effect — the throat is co-colonized with beta-lactamase p