Confusable diagnoses · PANCE / PANRE

Kawasaki Disease vs Scarlet Fever

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Kawasaki Disease and Scarlet Fever are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Kawasaki Disease vs Scarlet Fever at a glance

  • Kawasaki Disease: Self-limited medium-vessel vasculitis of young children; principal threat is coronary artery aneurysms; treated with IVIG and aspirin within 10 days of fever onset.
  • Scarlet Fever: Group A strep pharyngitis with toxin-mediated sandpaper rash, strawberry tongue, and Pastia lines; preventable sequelae include rheumatic fever and post-strep glomerulonephritis.

Try two board-style questions on Kawasaki Disease vs Scarlet Fever

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Question 1Infectious DiseaseMedium
A previously healthy 3-year-old boy is brought in for 6 days of fever to 40°C that has not responded to acetaminophen or ibuprofen. He has been markedly irritable. On exam he has bilateral conjunctival injection without discharge, bright red cracked lips with a strawberry tongue, and erythema and swelling of his palms and soles. A polymorphous truncal rash is present, and a single 2-cm anterior cervical lymph node is palpable. His throat is mildly erythematous without exudate. Which of the following is the most likely diagnosis?
  • AStrep scarlatina
  • BMeasles infection
  • CAdenoviral illness
  • DKawasaki disease
Reveal answer & full explanation
Correct answer: D — Kawasaki disease
  • AStrep scarlatina
  • BMeasles infection
  • CAdenoviral illness
  • DKawasaki disease✓

Why Kawasaki disease is correct

  • Classic Kawasaki requires fever >=5 days plus >=4 of 5 principal features; this child has all five: bilateral non-exudative conjunctivitis, lip/oral changes (cracked red lips, strawberry tongue), extremity changes (palmar/plantar erythema and edema), polymorphous rash, and unilateral cervical adenopathy >=1.5 cm.
  • Disproportionate irritability and antipyretic-resistant high fever in a child under 5 are characteristic supporting features.
  • Per AHA 2017 guidance, IVIG 2 g/kg plus aspirin within 10 days of fever onset reduces coronary aneurysm risk from 20-25% to roughly 3-5%, and an echocardiogram is mandatory.

Why the others are wrong

  • Strep scarlatina (scarlet fever) is group A strep with a sandpaper rash and strawberry tongue, but it lacks conjunctivitis and the palmar/plantar extremity changes seen here and typically follows exudative pharyngitis.
  • Adenoviral illness causes exudative conjunctivitis and pharyngitis with a shorter, self-limited fever course, not the non-exudative conjunctivitis, lip cracking, and extremity changes of this presentation.
  • Measles infection produces the three Cs (cough, coryza, conjunctivitis), Koplik spots, and a cephalocaudal rash, and does not cause strawberry tongue or palmar/plantar erythema and edema.
Question 2Infectious DiseaseMedium
A 7-year-old boy is brought to clinic in February with 2 days of sudden sore throat, fever to 39 °C, and a fine, blanching, sandpaper-textured erythematous rash that began in the axillae and groin. Exam shows tonsillar exudate, tender anterior cervical lymphadenopathy, circumoral pallor, and a bright red tongue with prominent papillae. A rapid antigen detection test on a throat swab is positive for group A Streptococcus. Which of the following is the most likely source of his infection?
  • AHis grandmother was diagnosed with shingles two weeks ago
  • BHe swam in a crowded community pool the week before he got sick
  • CA school classmate was sent home with hand-foot-mouth disease
  • DA sibling at home was treated for strep pharyngitis last week
Reveal answer & full explanation
Correct answer: D — A sibling at home was treated for strep pharyngitis last week
  • AHis grandmother was diagnosed with shingles two weeks ago
  • BHe swam in a crowded community pool the week before he got sick
  • CA school classmate was sent home with hand-foot-mouth disease
  • DA sibling at home was treated for strep pharyngitis last week✓

Why A sibling at home was treated for strep pharyngitis last week is correct

  • Scarlet fever is caused by exotoxin-producing strains of group A Streptococcus pyogenes; acquiring it requires exposure to the organism, which spreads by respiratory droplets and direct contact.
  • Close household or classroom contact with a person who has streptococcal pharyngitis is the strongest, most proximate risk factor because it supplies the actual source of the bacteria.
  • Winter-spring season and age 5-15 years raise baseline risk, but documented close contact with an infected person is the dominant driver in an individual case.

Why the others are wrong

  • His grandmother was diagnosed with shingles two weeks ago — herpes zoster is reactivated varicella-zoster virus; contact with its lesions can give a susceptible child primary varicella (itchy vesicles erupting in crops), not exudative pharyngitis with a sandpaper rash and a positive group A strep RADT.
  • He swam in a crowded community pool the week before he got sick — recreational water exposure is linked to organisms such as Pseudomonas or enteric pathogens, not droplet-spread group A Streptococcus.
  • A school classmate was sent home with hand-foot-mouth disease — HFMD is an enteroviral illness (usually coxsackievirus A16 or A6, or enterovirus A71) that causes painful oral ulcers and vesicles on the palms and soles; this exposure would not produce tonsillar exudate, a strawberry tongue, or a positive group A strep RADT.
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Side-by-side comparison

FeatureKawasaki DiseaseScarlet Fever
At a glanceSelf-limited medium-vessel vasculitis of young children; principal threat is coronary artery aneurysms; treated with IVIG and aspirin within 10 days of fever onset.Group A strep pharyngitis with toxin-mediated sandpaper rash, strawberry tongue, and Pastia lines; preventable sequelae include rheumatic fever and post-strep glomerulonephritis.
Classic presentationCracked red lips, strawberry tongue, red palms and soles, bilateral conjunctivitis, and a polymorphous rash in a febrile irritable toddler.; Fever ≥5 days, often 39-40 °C, unresponsive to antipyretics; Bilateral non-exudative conjunctival injection with limbic sparing; Lip changes: red, dry, cracked, fissured; strawberry tongue;…Child with strep throat, sandpaper rash with circumoral pallor, and strawberry tongue.; Sudden sore throat, fever (38-40 °C), headache, abdominal pain, nausea, and vomiting; Within 12-48 hours: fine, blanchable, erythematous papular rash starting in the groin, axillae, and neck; spreads to trunk and extremities with sandpaper texture;…
Workup / key labsClassic Kawasaki: fever ≥5 days plus ≥4 of 5 principal features (conjunctivitis, lip/oral changes, extremity changes, rash, cervical adenopathy). Suspected incomplete Kawasaki (fever ≥5 days with 2-3 features, or an infant ≤6 months with ≥7 days of unexplained fever): check CRP and ESR; if CRP ≥3.0 mg/dL and/or ESR ≥40 mm/h, treat when…Compatible clinical syndrome plus positive RADT or throat culture for group A strep.; Rapid antigen detection test (RADT) on throat swab — if negative in children/adolescents, follow with throat culture; Throat culture (gold standard); Anti-streptolysin O (ASO) and anti-DNase B antibodies for retrospective confirmation if needed; CBC:…
ImagingTransthoracic echocardiogram is mandatory and serial; ECG to detect arrhythmias and ischemia; Cardiac MRI or coronary CT for follow-up of aneurysmsNot required for routine diagnosis; Echocardiogram if rheumatic fever later develops
First-line treatmentIVIG + ASA for Kawasaki — IVIG 2 g/kg as a single infusion over 10-12 hours within 10 days of fever onset (and ideally before day 7); Moderate-dose (30-50 mg/kg/day) or high-dose (80-100 mg/kg/day) aspirin in 4 divided doses until afebrile for 48-72 hours, then low-dose aspirin 3-5 mg/kg/day until inflammatory markers and coronary…Penicillin V 500 mg PO BID-TID for 10 days (adults) or amoxicillin 50 mg/kg/day (children, divided BID or once daily) for 10 days — drug of choice; Benzathine penicillin G IM single dose if adherence concerns; Cephalexin or cefadroxil for 10 days as alternative; Penicillin-allergic without anaphylaxis: first-generation cephalosporin…

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Full outlines

Kawasaki Disease Scarlet Fever All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.