Overview
Slapped Cheek Syndrome (Erythema Infectiosum)
1. Clinical Overview
Summary
Slapped Cheek Syndrome (- historically "Fifth Disease") is a common viral exanthem caused by Parvovirus B19. It typically affects school-aged children, presenting with a mild prodrome followed by a characteristic "slapped cheek" facial rash and a lacy reticular rash on the body. While benign in healthy children, the virus has strong tropism for erythroid progenitor cells, making it dangerous for two specific groups: those with high red cell turnover (Sickle Cell/Thalassaemia/Spherocytosis) causing pure red cell aplasia, and pregnant women (risk of fetal anaemia and hydrops fetalis). Management is supportive for uncomplicated cases. [1,2]
Key Facts
- Causative Agent: Parvovirus B19 (single-stranded DNA virus).
- Infectivity: Highly infectious during the prodrome (fever/coryza). Not infectious once the rash appears.
- The Rash:
- Stage 1: Slapped cheek (bright red erythema).
- Stage 2: Reticular (lace-like) rash on trunk/limbs.
- Stage 3: Recurrent rash (triggered by heat/sunlight).
- Pregnancy Risk: Infection in pregnancy (especially less than 20 weeks) carries ~10% risk of fetal loss/hydrops.
- Aplastic Crisis: In patients with chronic haemolysis, B19 causes temporary cessation of red cell production (reticulocytopaenia) → profound anaemia.
Clinical Pearls
School Exclusion: There is NO need to keep a child with the rash off school. They were infectious last week when they just had a runny nose. By the time the cheeks are red, the infectious period is over.
"Gloves and Socks" Syndrome: A variant presentation (Papular-Purpuric Gloves and Socks Syndrome) presents with painful erythema and swelling of hands and feet. Unlike classic slapped cheek, these patients ARE infectious while the rash is present.
Adult Presentation: Adults (especially women) often get no rash but present with acute, symmetrical polyarthropathy (small joints of hands/feet) mimicking Rheumatoid Arthritis. It resolves in weeks-months.
The "Reticulocyte Count": In a child with Sickle Cell Disease presenting with severe anaemia, check the reticulocytes. Low reticulocytes = Aplastic Crisis (Parvovirus). High reticulocytes = Splenic Sequestration or Hyperhaemolysis.
2. Epidemiology
Incidence
- Seasonality: Peaks in late winter/spring. Epidemics every 3-4 years.
- Age: Peak 5-15 years.
- Seroprevalence: 50% of adults have IgG immunity (previous asymptomatic infection).
Transmission
- Route: Respiratory droplets. Also vertical (mother-to-fetus) and blood products.
- Incubation: 4-14 days (up to 21 days).
- Secondary Attack Rate: 50% in households.
3. Pathophysiology
Viral Tropism
- Parvovirus B19 binds to the P antigen (globoside) receptor on erythroid progenitor cells in the bone marrow.
- It is cytotoxic to these cells.
Impact on Erythropoiesis
- Infection causes transient arrest of erythropoiesis (7-10 days).
- Healthy Host: Red cell lifespan is 120 days. A 10-day pause has minimal effect (mild asymptomatic Hb drop).
- High Turnover Host (Sickle, Thalassaemia): Red cell lifespan is short (10-20 days). A 10-day pause causes profound anaemia ("Transient Aplastic Crisis").
- Fetus: Fetal red cells have shorter lifespan and rapidly expanding volume. Arrest can cause severe fetal anaemia → High output cardiac failure → Hydrops Fetalis.
Mechanism of Rash/Joints
- Mediated by immune complex deposition (Antibody-Antigen complexes) in skin and synovium.
- This occurs after the viraemia clears (hence non-infectious).
4. Clinical Presentation
Paediatric Presentation (Classic)
- Prodrome (Infectious Phase): Fever, coryza, headache, mild nausea (lasts 2-3 days).
- Exanthem Phase (Non-infectious):
- Facial: Bright red erythema on cheeks. Spares nasolabial folds and periorbital area.
- Truncal: 1-4 days later. Maculopapular rash fading to "lacy" or reticular pattern on limbs/trunk.
- Course: Fades over 1-3 weeks. Can reappear with heat/exercise/stress.
Adult Presentation
Aplastic Crisis Presentation
Arthropathy
50% of infected adults. Symmetrical, peripheral polyarthritis (hands, wrists, knees). Can last weeks/months.
Rash
Often absent or atypical.
Constitutional symptoms.
Common presentation.
5. Clinical Examination
Inspection
- Face: Intense erythema ("Slapped"). Circumoral pallor.
- Body: Reticular pattern (looks like net curtains).
- Joints: Swelling/tenderness (adults).
Assessment
- Signs of Anaemia: Pallor, tachycardia, flow murmur.
6. Investigations
Healthy Child
- Clinical Diagnosis: No investigations needed.
Indications for Serology
- Pregnant woman exposed to Parvovirus.
- Immunocompromised patient.
- Investigation of non-immune hydrops.
- Investigation of unexplained arthritis.
Interpretation:
- IgM + / IgG -: Acute infection (0-3 months).
- IgM + / IgG +: Recent infection (protective immunity developing).
- IgM - / IgG +: Past infection (Immune). Safe.
- IgM - / IgG -: Susceptible (Non-immune). Risk.
Indications for PCR
- Immunocompromised patients (may not mount antibody response).
- Amniotic fluid (fetal diagnosis).
Low Hb Assessment
- FBC: Severe anaemia (Hb less than 60g/L).
- Reticulocytes: Reticulocytopaenia (less than 0.2% or absent).
7. Management
Management Algorithm
SUSPECTED PARVOVIRUS
(Rash or Exposure)
↓
┌─────────────────────────────────────────────┐
│ RISK ASSESSMENT │
│ - Pregnant? │
│ - Haemolytic Anaemia (Sickle)? │
│ - Immunocompromised? │
└─────────────────────────────────────────────┘
↙ YES NO ↘
SPECIALIST CARE REASSURANCE
(See below) - Symptomatic care
- School ok if rash present
1. Uncomplicated Cases (Healthy Child)
- Supportive: Paracetamol/Ibuprofen for fever/pain.
- Education: Explain rash recurrence with heat.
- School: No exclusion necessary.
2. Pregnancy Exposure
Refer to RCOG Guidelines [3].
- Confirm Exposure: Significant contact?
- Check Maternal Serology:
- IgG positive: Immune. Reassure. (Most common outcome).
- IgG negative, IgM negative: Susceptible. Repeat serology in 4 weeks.
- IgM positive: Acute infection. Referral to Fetal Medicine.
- Fetal Monitoring (if maternal infection confirmed):
- Weekly Middle Cerebral Artery (MCA) Doppler ultrasound for 12 weeks.
- Anaemic fetuses shunt blood to brain (High MCA Velocity).
- If Hydrops develops: Intra-uterine transfusion.
3. Transient Aplastic Crisis
- Admit: Oxygen, monitoring.
- Transfusion: Packed red cells. Usually curative (marrow recovers in 1-2 weeks).
- Isolation: Important in hospital to protect other at-risk patients (infectious phase may persist).
8. Complications
Disease Complications
- Arthropathy: usually self-limiting but can persist months.
- Aplastic Anaemia: In vulnerable hosts.
- Chronic Pure Red Cell Aplasia: In immunocompromised (e.g., HIV, Chemo) who cannot clear virus. Requires IVIG.
- Myocarditis/Hepatitis: Rare manifestations.
Pregnancy Complications
- First 20 weeks: Risk of miscarriage (~10%) and Hydrops Fetalis (~3%).
- >20 weeks: Risk is very low.
- Teratogenicity: No evidence of congenital malformations (unlike Rubella/Zika).
9. Prognosis and Outcomes
Healthy Children
- Excellent. Full recovery.
- Rash usually clears in 1-3 weeks.
Fetal Hydrops
- If untreated: High mortality.
- With intrauterine transfusion: >80% survival.
10. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Parvovirus B19 in Pregnancy | RCOG (Green-top 4) | Algorithm for testing and referral. MCA Doppler definition. |
| Viral Rash in Pregnancy | PHE (UKHSA) | Testing pathway. |
| Sickle Cell Management | SHC / ASH | Transfusion thresholds for aplastic crisis. |
Landmark Studies
1. Enders et al. (2004)
- Question: Risk of fetal death after B19?
- Result: Overall fetal death rate 6.3% (highest less than 20 weeks).
- Impact: Defined risk counselling data.
2. Fairley et al. (1995)
- Observation: Retrospective look at hydrops.
- Result: Spontaneous resolution of hydrops occurs in ~30%, but transfusion improves survival.
11. Patient and Layperson Explanation
What is Slapped Cheek Syndrome?
It is a very common childhood virus. It is spread by coughing and sneezing.
Why the name?
It causes a bright red rash on the cheeks, looking like the child has been slapped. A lacy pink rash often follows on the body.
Is it contagious?
- Yes, BUT only before the rash appears (when the child just has a cold/fever).
- Once the rash appears, the child is no longer contagious. They can go to school if they feel well enough.
Is it dangerous?
- For most children: No. It is mild and goes away on its own.
- In Pregnancy: If a pregnant woman (who hasn't had it before) catches it, there is a small risk it can cause anaemia in the baby.
- Blood Conditions: If a child has Sickle Cell anaemia, this virus can make their anaemia suddenly much worse and they may need hospital care.
Treatment
- Rest and fluids.
- Paracetamol for fever.
- No special medicines needed for healthy children.
- The rash may fade and come back when the child is hot (bath/running) for a few weeks - this is normal.
12. References
Primary Sources
- Young NS, Brown KE. Parvovirus B19. N Engl J Med. 2004;350:586-597. PMID: 14762186.
- Heegaard ED, Brown KE. Human parvovirus B19. Clin Microbiol Rev. 2002;15:485-505. PMID: 12097253.
- RCOG. Parvovirus B19 Infection in Pregnancy (Green-top Guideline No. 4). 2014.
- Public Health England. Guidance on the investigation, diagnosis and management of viral illness, or exposure to viral rash illness, in pregnancy. 2019.
13. Examination Focus
Common Exam Questions
- Paediatrics: "A child with Slapped Cheek rash wants to return to school. Advice?"
- Answer: Allowed. Not infectious once rash appears.
- Obstetrics: "Pregnant woman (28 weeks) exposed to B19. IgM+, IgG-. Next step?"
- Answer: Refer Fetal Medicine for MCA Dopplers (screen for fetal anaemia).
- Haematology: "Mechanism of anaemia in Parvovirus B19?"
- Answer: Lysis of erythroid progenitor cells (arrest of erythropoiesis).
- Rheumatology: "Young woman, sudden symmetrical hand arthritis, RhF negative. Recent cold. Diagnosis?"
- Answer: Parvovirus Arthritis.
Viva Points
- MCA Doppler: Why? Anaemia lowers blood viscosity -> increases velocity of flow. Non-invasive test for fetal anaemia.
- P Antigen: The receptor used by the virus. People lacking P antigen (rare) are immune.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.