'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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Question 1Infectious DiseaseMedium
A 9-year-old boy with homozygous sickle cell disease is brought to the emergency department with 3 days of fatigue, pallor, and shortness of breath. He attends a public elementary school, has a 4-year-old sibling who recently had a cold, and received his annual inactivated influenza vaccine 2 weeks ago. On exam he is pale and tachycardic. Hemoglobin is 4.2 g/dL (baseline 8.5 g/dL) with a markedly low absolute reticulocyte count, and parvovirus B19 IgM is positive. Which of the following is the strongest risk factor for this patient developing transient aplastic crisis?
- AAttendance at a public grade school
- BHousehold contact with a recent illness
- CAbsence of prior parvovirus B19 immunity
- DUnderlying chronic hemolytic anemia
Reveal answer & full explanation
Correct answer: D — Underlying chronic hemolytic anemia
- AAttendance at a public grade school
- BHousehold contact with a recent illness
- CAbsence of prior parvovirus B19 immunity
- DUnderlying chronic hemolytic anemia✓
Why Underlying chronic hemolytic anemia is correct
- Parvovirus B19 binds the P antigen (globoside) on erythroid progenitors and halts erythropoiesis, producing transient reticulocytopenia.
- In a healthy child this brief shutdown is silent because the normal red cell lifespan is ~120 days. In sickle cell disease (or other chronic hemolytic anemias such as hereditary spherocytosis or thalassemia), red cell survival is drastically shortened, so even a few days of arrested erythropoiesis cause the abrupt hemoglobin drop with a low reticulocyte count seen here, the defining feature of transient aplastic crisis.
- This underlying hemolytic state, not the exposure route, is what converts a benign childhood exanthem into a life-threatening event, making it by far the strongest risk factor.
Why the others are wrong
- Attendance at a public grade school — School and daycare exposure raises the chance of acquiring parvovirus B19, but it explains how the infection was caught, not why the marrow failed; most exposed children have mild illness or none.
- Household contact with a recent illness — A sibling with coryza is a plausible droplet source, but acquiring the virus is not what determines severity; the host's marrow reserve is.
- Absence of prior parvovirus B19 immunity — Being seronegative makes infection possible but, like the other exposure factors, governs susceptibility to infection rather than the catastrophic anemia, which depends on the shortened red cell lifespan of hemolytic disease.
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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