'Slapped cheek' facial rash followed by lacy reticular truncal rash in school-age children; risks include aplastic crisis in hemolytic anemias and hydrops fetalis in pregnancy.
Also known as: fifth disease, 5th disease, parvovirus B19, slapped cheek syndrome, erythema infectiosum
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Risk factors
- School and daycare exposure
- Pregnancy without prior immunity (highest risk weeks 13-20 for hydrops fetalis)
- Chronic hemolytic anemia (sickle cell, hereditary spherocytosis, thalassemia) — risk of transient aplastic crisis
- Immunocompromise (pure red cell aplasia and chronic anemia)
Pathophysiology
Virus binds the P antigen (globoside) on erythroid progenitors, halting erythropoiesis and producing transient reticulocytopenia. The classic exanthem is immune-complex-mediated and appears as viremia resolves, explaining lack of contagiousness when the rash is visible.
Clinical presentation
Symptoms
- Mild prodrome with low-grade fever, headache, coryza 5-7 days earlier (often missed)
- Stage 1 — bright erythematous 'slapped cheek' rash with circumoral pallor
- Stage 2 — lacy, reticular maculopapular rash on extensor surfaces of arms, then trunk and legs, lasting 1-3 weeks; recurs with sun, heat, exercise
- Adults: arthralgias and symmetric polyarthritis of hands, wrists, knees, ankles; rash often subtle or absent
Signs / physical exam
- Slapped-cheek facies
- Lacy/reticular rash that waxes and wanes with temperature and sunlight
- Symmetric small-joint synovitis without joint destruction
- Pallor or jaundice in patients with aplastic crisis
Classic findings
Bright red 'slapped cheeks' with circumoral pallor in a school-age child.
Differential diagnosis
- Rubella — Posterior auricular nodes, head-to-toe rash, vaccine history
- Measles — Three Cs, Koplik spots, cephalocaudal rash
- Roseola — Younger child, high fever resolves as rash appears
- Drug eruption — Recent new medication; no facial slapped-cheek pattern
- Systemic lupus / juvenile dermatomyositis — Persistent malar rash with systemic features
- Scarlet fever — Sandpaper rash, strep throat, Pastia lines
Diagnostic workup
Diagnostic criteria
Clinical syndrome supported by IgM positivity or PCR (in atypical/high-risk hosts).
Labs
- Clinical diagnosis in immunocompetent children with classic rash
- Parvovirus B19 IgM (acute), IgG (immunity) — preferred in pregnancy and adult arthralgia
- Parvovirus B19 DNA PCR for immunocompromised, fetal, and aplastic crisis cases
- CBC with reticulocyte count in patients with hemolytic anemia — low reticulocytes during aplastic crisis
Imaging
- Fetal ultrasound (every 1-2 weeks for 8-12 weeks after maternal exposure) — measure middle cerebral artery peak systolic velocity for fetal anemia
- MCA-PSV >1.5 MoM suggests fetal anemia and prompts referral for possible intrauterine transfusion
Treatment
First-line
- Supportive care: antipyretics, antihistamines for pruritus
- No isolation needed once rash appears (patient is no longer infectious)
- NSAIDs for adult arthralgias (self-limited, no joint destruction)
Transient aplastic crisis (sickle cell, hemolytic anemias)
- Hospitalize, monitor hemoglobin, transfuse PRBCs as needed
- Droplet and contact isolation (these patients ARE still contagious because viremia persists)
Pregnancy exposure
- Check maternal IgG/IgM
- If seroconverts, serial ultrasound with MCA Doppler
- Refer to maternal-fetal medicine if hydrops fetalis suspected; intrauterine transfusion may be life-saving
Immunocompromised (chronic anemia/pure red cell aplasia)
- IVIG (parvovirus B19 has no specific antiviral) — clears persistent viremia in many
- Reduce immunosuppression if feasible
Second-line / adjunct
- Reassure pregnant patients: most exposures do NOT result in hydrops fetalis; baseline fetal loss risk <5% overall
Complications
- Transient aplastic crisis in hemolytic anemia
- Pure red cell aplasia in immunocompromised hosts (HIV, post-transplant)
- Hydrops fetalis and fetal loss (highest risk weeks 13-20)
- Adult symmetric polyarthropathy (transient, no destruction)
- Rare: myocarditis, glomerulonephritis, hepatitis, encephalopathy
PANCE pearls
- Rash appears AFTER contagiousness has ended — no isolation needed for typical erythema infectiosum.
- Sickle cell + parvovirus = transient aplastic crisis; these patients ARE still contagious and need isolation.
- Pregnancy exposure before 20 weeks → check IgM/IgG and arrange MCA Doppler surveillance.
- Adults more often present with symmetric polyarthropathy than rash — consider parvovirus in seronegative adult inflammatory arthritis.
- IVIG is the treatment for parvovirus B19 in the immunocompromised — there is no antiviral.
References
- AAP Red Book — American Academy of Pediatrics Red Book — Parvovirus B19 chapter
- ACOG — ACOG Practice Bulletin — Management of Pregnancy Complicated by Parvovirus B19 Exposure
- CDC — CDC Clinical Overview of Parvovirus B19
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