Fifth Disease (Erythema Infectiosum)
Fifth disease is a self-limited viral exanthem caused by parvovirus B19 that requires only supportive care in healthy children and adults, with diagnosis made clinically based on the characteristic "slapped cheek" appearance and lacy reticular rash. 1
Clinical Features
Classic Presentation in Children
The disease evolves through three distinct stages:
Stage 1 (Days 0-2):
- Bright erythematous rash on both cheeks creating the pathognomonic "slapped cheek" appearance
- Circumoral pallor (sparing around the mouth)
- Mild prodromal symptoms may precede: low-grade fever, headache, malaise, myalgia 1
Stage 2 (Days 1-4 after facial rash):
- Diffuse macular erythema spreads to trunk, extremities, and buttocks
- More intense on extensor surfaces
- Palms and soles typically spared
- Central clearing creates characteristic lacy or reticulated pattern 1
Stage 3 (Weeks 1-3):
- Evanescence and recrudescence of rash
- Triggered by sunlight, heat, exercise, emotional stress
- Rash resolves spontaneously within three weeks 1
Adult Presentation
Adults present differently than children:
- Only 20% develop facial erythema
- Rash more commonly on legs (most frequent), then trunk, then arms
- Reticulated/lacy pattern in 80% of cases
- Pruritus in approximately 50% 1
- Arthropathy is the dominant manifestation - symmetric polyarthralgia/arthritis affecting hands, wrists, knees, ankles 2
Key Epidemiologic Features
- Incubation period: 4-14 days
- Peak age: 4-10 years old
- Transmission: respiratory secretions, saliva
- Contagious during prodrome, not contagious once rash appears 1
Diagnosis
Clinical diagnosis is sufficient in typical cases - no laboratory testing needed for straightforward presentations 1, 3.
When to Consider Laboratory Testing
Order parvovirus B19 IgM and IgG serology when:
- Pregnant patient with exposure (critical for fetal risk assessment) 4
- Immunocompromised patient
- Patient with chronic hemolytic anemia (risk of aplastic crisis)
- Atypical presentation requiring confirmation 1
Differential Diagnosis to Exclude
The lacy reticular pattern helps distinguish from:
- Viral exanthems: Roseola (HHV-6), enteroviral infections, EBV - lack the slapped cheek and lacy pattern 5
- Scarlet fever: Sandpaper texture, strawberry tongue, circumoral pallor different from slapped cheek 6
- Kawasaki disease: Requires fever ≥5 days plus 4 of 5 criteria (conjunctivitis, oral changes, extremity changes, rash, lymphadenopathy) 6
- Drug reactions: History of new medication
- Lyme disease (erythema migrans): Single expanding lesion with central clearing, not diffuse lacy pattern 7
Management
Healthy Children and Adults
Supportive care only:
- Reassurance about self-limited course
- Antipyretics for fever (acetaminophen or ibuprofen)
- Antihistamines for pruritus if present
- No isolation needed once rash appears (no longer contagious) 1, 3
Adults with Arthropathy
For significant joint symptoms:
- NSAIDs (naproxen) as first-line
- Consider short course of corticosteroids for severe cases
- Conservative physical therapy, joint mobilization may provide adjunctive benefit 2
- Symptoms typically resolve within weeks to months
High-Risk Populations Requiring Specialist Consultation
Pregnant women with confirmed acute infection:
- Risk of fetal hydrops fetalis (approximately 10% if infected in first 20 weeks)
- Serial ultrasounds every 1-2 weeks for 8-12 weeks to monitor for hydrops
- Refer to maternal-fetal medicine for intrauterine transfusion if hydrops develops 4
Immunocompromised patients:
- Risk of chronic anemia/pure red cell aplasia
- May require IVIG therapy
- Infectious disease consultation recommended 1
Patients with chronic hemolytic anemia (sickle cell, hereditary spherocytosis):
- Risk of transient aplastic crisis
- Monitor hemoglobin closely
- May require transfusion support 1
Critical Pitfalls to Avoid
Do not isolate patients once rash appears - they are no longer contagious, unlike measles or other viral exanthems where isolation continues during rash phase
Do not miss pregnancy status - always ask about pregnancy in women of childbearing age, as fetal complications are the primary serious concern
Do not confuse with Kawasaki disease - Fifth disease lacks the prolonged fever, conjunctivitis, and oral/extremity changes of Kawasaki; missing Kawasaki risks coronary artery aneurysms
Recognize that facial rash is often absent in adults - arthropathy may be the only manifestation, leading to misdiagnosis as rheumatoid arthritis or other inflammatory arthritis
Remember recrudescence is normal - warn patients the rash may come and go for weeks with triggers like sun exposure; this does not indicate treatment failure or reinfection