Explaining fifth disease and protecting the pregnant contact — OSCE

Candidate instructions (8-minute station)

You are the paediatric registrar in the emergency department. A 6-year-old child was sent home from school yesterday with intensely red slapped cheeks and a lacelike rash on the arms and thighs; the diagnosis is erythema infectiosum (fifth disease), caused by parvovirus B19, made on the clinical pattern. The child is afebrile, well and playing. The child's mother, who is twenty weeks pregnant, is in the room and is anxious. [1]

Your tasks are: [1]

1. Explain the diagnosis of fifth disease and what the rash will do over the coming weeks, in plain, reassuring language. [1]
2. Explain the infectivity paradox — that the child is contagious before the rash and is no longer contagious now the rash is visible — and what it means for school and household contacts. [2]
3. Explain why the mother, at twenty weeks pregnant, needs same-day parvovirus B19 serology, what the results will mean, and the surveillance pathway if she is non-immune. [3]
4. Address the parent's anxiety about the unborn baby honestly, including that timely surveillance and intrauterine transfusion give an excellent outcome. [3]

You are not expected to manage the pregnancy yourself — flag that the mother needs same-day review by the maternity and fetal-medicine team because the surveillance window is time-critical. [3]

Examiner prompt to the actor (parent)

"But she's so well — surely it's just a childhood rash? The school said it's slapped cheek and it's going round, nothing to worry about. Why are you suddenly talking about blood tests for me and the baby when it's my daughter who has the rash? Is the baby in danger? And she's already got the rash, so should I keep her home from school?" [2]

Marking domains

• Frame and explanation of the child's illness (3): explains fifth disease as a common, benign viral rash caused by parvovirus B19; describes the slapped-cheek-then-lace pattern; explains that the lacelike rash may fluctuate with heat, sunlight and bathing for weeks and that this is expected and not a sign of ongoing infection or treatment failure; confirms the child is well and needs no tests or treatment. [1]
• The infectivity paradox and public-health plan (3): explains clearly and without jargon that the child was contagious in the days before the rash appeared and is no longer contagious now the rash is visible, so keeping her home on grounds of infectivity is not necessary — local guidance may exclude only while she is systemically unwell; identifies that the silent exposures happened a week earlier, which is why the pregnant contact matters. [2]
• Protecting the pregnant contact (3): explains that the mother, at twenty weeks, is exactly the contact we protect — that a single blood test for IgG and IgM will tell us whether she is immune (protected, no risk) or susceptible (at risk of primary infection); that if she is non-immune and seroconverts the fetus is at risk of anaemia and hydrops; that she needs serial ultrasound for ten to twelve weeks and fetal-medicine referral; and that timely intrauterine transfusion can save an affected fetus. Frames this as detectable and treatable, time-critical and same-day. [3] [1]
• Communication (1): acknowledges the parent's anxiety and the counter-intuitive idea that the well child is not the concern but the pregnant mother is; uses plain language, avoids jargon, checks understanding, and frames the pathway positively without trivialising the fetal risk. [3]

Model answer — the explanatory script

"Thank you for coming in. The good news first: your daughter is fine. What she has is fifth disease — slapped cheek syndrome — and it's a common, mild viral illness of childhood caused by a virus called parvovirus B19. The bright red cheeks and the lacelike rash on her arms and legs are exactly what we expect, and she's well in herself, which is why she doesn't need any blood tests or any treatment. She'll get better on her own." [1]

"One thing worth knowing about the rash — it can come and go. Heat, sunlight, a warm bath or exercise can bring it back over the next few weeks, even after it seems to have gone. That doesn't mean she's getting sick again or that the treatment isn't working — it's just how this rash behaves, and it's not a sign she's still infectious. It will settle on its own." [1]

"On keeping her home from school — and I know that seems odd when she has a rash — the thing to understand is the timing. Fifth disease is actually contagious in the days before the rash appears, when the child just has a mild cold or nothing at all. By the time the cheeks go red and the rash comes out, the child is no longer contagious. So your daughter, with the rash visible now, has already done her exposing — keeping her home now won't stop anyone catching it, because that window closed a week ago. Most schools only ask children to stay home while they're genuinely unwell, not for the rash itself." [2]

"Now — and this is the part that matters most — I want to talk about you and the baby, because you're twenty weeks pregnant. The same virus that causes this trivial rash in your daughter can, in a woman who hasn't had it before, cross the placenta and affect the baby's blood production. I'm not saying that has happened — I'm saying we need to find out, today, whether you're protected." [3]

"What I'd like to do is a single blood test that checks two things — antibodies called IgG and IgM. If the IgG is positive, it means you've had this virus before, you're immune, and the baby is completely safe — nothing more to do. If it's negative, it means you haven't had it and you could be at risk, and we'd watch you carefully over the next ten to twelve weeks with ultrasound to check the baby's wellbeing." [1]

"If the ultrasound ever showed the baby was becoming anaemic — and I want to stress this can be treated — we'd involve our fetal-medicine team, and a transfusion given to the baby before birth can correct the problem completely. So this is very much a 'let's find out and watch' situation, and the outcome with timely care is excellent. What I don't want is for us to wait and see without checking, because the window to act is narrow." [3]

"So my plan today is: your daughter needs nothing but reassurance and normal activities. For you, I'd like to take that blood test now, and I'll arrange for our maternity and fetal-medicine team to see you today or tomorrow so there's a clear surveillance plan in place. Does that make sense, and what questions do you have?" [3] [1]