What are the signs and symptoms of scarlet fever in a child or adolescent with a penicillin allergy?

Signs and Symptoms of Scarlet Fever

Scarlet fever presents with a distinctive triad: sore throat, fever, and a characteristic sandpaper-like rash, though the rash typically appears 1 day after other symptoms begin. 1, 2, 3

Core Clinical Features

Initial Presentation (Before Rash)

• Fever occurs in 89% of cases, with temperature >38°C in 73% 3
• Sore throat is the primary early symptom, especially in children ≥5 years old 3, 4
• Enlarged cervical lymph nodes appear in 70% of cases 3
• Absence of cough in 73% of patients (helps distinguish from viral illness) 3

The Characteristic Rash

• Sandpaper-like, papular texture that is pathognomonic for scarlet fever 1, 2, 5
• Timing: Rash appears in 89% of cases but follows onset of other symptoms by a median of 1 day in 71% of patients 3, 4
• This delayed rash appearance is a critical diagnostic pitfall—scarlet fever may be initially misdiagnosed as viral pharyngitis before the rash emerges 4

Oral Manifestations

• "Strawberry tongue" or "raspberry tongue" is a distinctive finding that dental and medical professionals should recognize 5
• Tonsillar exudate appears in only 24% of cases, making it an unreliable diagnostic feature 3

Age-Related Variations

Younger Children (<4 years)

• Higher fever (>38°C) occurs significantly more often than in older children (80% vs 63%; OR 3.13) 3
• Sore throat less prominent at initial presentation 3
• Most cases occur in this age group, with median age of 3.8 years 3

Older Children (≥5 years)

• Sore throat more common at onset (OR 3.1 compared to younger children) 3, 4
• Higher risk of delayed diagnosis when presenting with sore throat, as it mimics viral pharyngitis (OR 2.8 for delayed diagnosis) 4

Critical Diagnostic Pitfalls

In 28% of cases at first consultation, scarlet fever is not initially considered, with symptoms frequently misattributed to viral infection (60% of missed cases). 4

• The rash is the key diagnostic feature, regardless of patient age 3
• Traditional clinical prediction rules (Centor, McIsaac scores) perform poorly for scarlet fever—86% of cases score ≤2 points on Centor 3
• Delayed diagnosis results in an average 1-day longer recovery time and increased risk of complications 4

Management Implications for Penicillin-Allergic Patients

Low-Risk Penicillin Allergy History

For children with a history of benign cutaneous reactions (maculopapular rash or urticaria without systemic symptoms) occurring >1 year ago, proceed directly to a single-dose amoxicillin challenge without prior skin testing. 6, 7, 8

• Over 90% of children labeled "penicillin allergic" tolerate the drug on re-exposure 7, 9
• Direct challenge has 5-10% reaction rates, generally no more severe than the original reaction 7

High-Risk Features Requiring Allergy Evaluation

Perform penicillin skin testing before treatment if the patient has history of:

• Anaphylaxis, angioedema, or respiratory/cardiovascular symptoms 6, 7, 8
• Blistering, skin exfoliation, or mucosal involvement 7, 8
• Severe reactions occurring <1 year ago 8

Alternative Antibiotics

If true penicillin allergy is confirmed:

• Carbapenems can be safely administered without prior testing due to dissimilar molecular structure 9
• Third-generation cephalosporins with dissimilar R1 side chains have <1% cross-reactivity risk 9
• Avoid all other penicillins and first/second-generation cephalosporins 7, 9

Complications of Untreated Disease

Early antibiotic treatment is critical to prevent serious sequelae:

• Acute rheumatic fever 1, 5
• Glomerulonephritis 1, 5
• Endocarditis 1, 5
• Bacteremia and meningitis 1
• Pneumonia 1

Streptococcus pyogenes causes over 500,000 deaths annually worldwide, making prompt recognition and treatment essential. 5