Measles vs Scarlet Fever
Measles 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.
Measles vs Scarlet Fever at a glance
- Measles: Highly contagious paramyxovirus with prodromal cough/coryza/conjunctivitis and Koplik spots, followed by cephalocaudal maculopapular rash; vaccine-preventable.
- 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.
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Side-by-side comparison
| Feature | Measles | Scarlet Fever |
|---|---|---|
| At a glance | Highly contagious paramyxovirus with prodromal cough/coryza/conjunctivitis and Koplik spots, followed by cephalocaudal maculopapular rash; vaccine-preventable. | Group A strep pharyngitis with toxin-mediated sandpaper rash, strawberry tongue, and Pastia lines; preventable sequelae include rheumatic fever and post-strep glomerulonephritis. |
| Classic presentation | Three Cs + Koplik spots + cephalocaudal rash in an unvaccinated child.; Prodrome (3-5 days): high fever (often 40 °C), cough, coryza, conjunctivitis (the three Cs), malaise; Koplik spots: 1-2 mm bluish-white papules on a red base on buccal mucosa opposite molars, 1-2 days before rash; Rash: erythematous maculopapular eruption beginning… | 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 labs | Clinical case definition (fever, generalized maculopapular rash ≥3 days, plus cough/coryza/conjunctivitis) confirmed by IgM positive or RT-PCR positive.; Measles-specific IgM and IgG (acute and convalescent); RT-PCR on nasopharyngeal swab, throat swab, urine, or blood — most sensitive within the first 5 days; Report immediately to… | 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:… |
| Imaging | Chest x-ray if pneumonia suspected | Not required for routine diagnosis; Echocardiogram if rheumatic fever later develops |
| First-line treatment | Supportive care: antipyretics, hydration, isolation (airborne precautions for 4 days after rash onset); Vitamin A: 200,000 IU PO on days 1 and 2 (50,000 IU if <6 months, 100,000 IU if 6-11 months) — WHO/AAP recommend for all children with measles; reduces mortality and ocular complications; Post-exposure prophylaxis: MMR vaccine within… | 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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