Slapped cheek is one of those childhood illnesses that causes little concern in the child having it, but can matter significantly in the households and schools where exposure occurs. The illness is typically mild — a child who looks like they've been slapped on both cheeks, followed by a lacy rash on the body and sometimes joints, and then recovery. The complication is not in the child.
Parvovirus B19 in a pregnant woman, particularly in the first twenty weeks of pregnancy, can infect foetal red blood cell precursors, causing severe foetal anaemia. In a proportion of cases this leads to hydrops fetalis — a serious and potentially fatal accumulation of fluid in foetal tissues. Around 50 to 60 per cent of adults are immune (from prior infection) and have no risk, but a pregnant woman who is not immune and is exposed deserves prompt assessment.
Healthbooq (healthbooq.com) covers common childhood infectious diseases.
The Illness in Children
Slapped cheek disease (fifth disease, erythema infectiosum) is caused by parvovirus B19, a small DNA virus. It primarily infects erythroid progenitor cells (the precursor cells of red blood cells) in bone marrow. In healthy children with normal haemoglobin, this brief suppression of red cell production has no significant effect.
The illness has a distinctive two-stage presentation. The prodromal stage (seven to ten days after infection) consists of a mild fever, runny nose, and general malaise — entirely non-specific. Then comes the rash: a bright, intensely red rash on both cheeks (the "slapped" appearance), which may be mildly warm but is not usually painful. One to four days later, a lacy, reticular (net-like) rash appears on the trunk and limbs. This lacy rash can recur with heat, exercise, or sunlight for several weeks.
Some children — and many adults with the primary infection — also develop joint pain (arthralgia), often affecting small joints of the hands and feet. This is more common in adults than children and is self-limiting.
Contagiousness
This is the key practical point: children are most contagious during the prodromal phase, before the rash appears. By the time the characteristic facial rash develops, the child is no longer contagious. Excluding a child from school because of the facial rash is therefore unnecessary and does not protect contacts.
The virus spreads via respiratory droplets and direct contact with infected secretions. The incubation period is four to twenty-one days.
Who Is at Risk from Serious Complications
Pregnant women: parvovirus B19 can cross the placenta and infect foetal erythroid precursor cells. The foetal bone marrow is very active producing red cells for a rapidly growing organism, and suppression of this leads to foetal anaemia. In severe cases, hydrops fetalis (fluid accumulation in body cavities and tissues due to heart failure from anaemia) develops, which can be fatal. The risk is highest in the first twenty weeks of pregnancy; after this, the foetus can more easily compensate for the anaemia.
The risk of foetal complications following maternal infection is estimated at around 3 per cent overall, but up to 10 per cent if infection occurs before twenty weeks. Maternal infection does not always reach the foetus — around half of infections do not cross the placenta.
Any pregnant woman who has been exposed to a confirmed or suspected case of slapped cheek should contact her GP or midwife on the same day for a blood test to check immunity status and, if susceptible, for close monitoring.
People with haemolytic anaemia (such as sickle cell disease or hereditary spherocytosis): parvovirus B19 can trigger a transient aplastic crisis — a sudden severe drop in haemoglobin — in people whose red cells have a shortened lifespan. This can be life-threatening. These individuals should also be assessed promptly on exposure.
Immunocompromised individuals may develop chronic parvovirus B19 infection with persistent anaemia requiring specific treatment.
Treatment
No antiviral treatment exists for parvovirus B19 in otherwise healthy children. Management is symptomatic: paracetamol or ibuprofen for fever and joint pain, reassurance, and adequate fluid intake. The illness resolves without complications in healthy children.
For foetal hydrops caused by parvovirus infection, intrauterine blood transfusion is sometimes performed by foetal medicine specialists.
Exclusion from School
Not required once the rash is visible — the child is no longer contagious at that stage. School attendance is appropriate if the child feels well enough.
Key Takeaways
Slapped cheek disease (fifth disease, erythema infectiosum) is a common viral childhood illness caused by parvovirus B19. It causes a bright red rash on the cheeks followed by a lacy rash on the body. By the time the rash appears, the child is no longer contagious. The illness is mild and self-limiting in healthy children. However, parvovirus B19 infection during pregnancy — particularly in the first half — can cause foetal anaemia and hydrops fetalis, and should prompt urgent assessment by a GP or obstetrician. Pregnant women who are unaware of their immunity status and have been exposed should seek same-day advice.
