Varicella exposure in a child on alternate-day prednisolone
A 6-year-old girl with steroid-sensitive nephrotic syndrome in remission has been taking prednisolone 20 mg on alternate days (2 mg/kg on the dosing day) for 11 weeks. She attends the day unit for a routine blood pressure check. A child who sat next to her in the waiting room for 40 minutes that morning is later found to have chickenpox; the rash began the next day and the two children shared a box of crayons. The girl has no documented varicella and has never been vaccinated against it. Her mother says she had 'a mild rash' at about 2 years of age, but it was never diagnosed and there is no record. It is now 24 hours since the exposure. She is afebrile and well, with no rash. The unit has no varicella zoster immune globulin (VZIG) on site; the pharmacy can obtain it in 48 hours. The mother asks whether the steroid should be stopped and whether 'getting it over with now' would be better than later.
1. Stratify this child's risk and decide between VZIG, oral aciclovir prophylaxis and observation. Justify the timings.
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Risk stratification: significant exposure (indoor, 40 minutes, face-to-face sharing of objects) in a child with no reliable history of varicella and no vaccination. She is immunosuppressed by 2 mg/kg prednisolone on alternate days for 11 weeks - above the threshold dose and duration usually used to define significant immunosuppression. She is therefore at risk of severe varicella, including haemorrhagic or disseminated disease and pneumonitis, not just a bad rash.
Decision: she should receive post-exposure prophylaxis. The order of preference:
- VZIG as soon as possible - ideally within 72-96 hours of exposure, and it can still be considered up to 10 days. If the pharmacy can supply it at 72 hours from exposure (48 hours from now), that is still within the effective window and is the best option for a significantly immunosuppressed child, because it is passive antibody rather than a drug that needs to be started at a specific point in the incubation period.
- If VZIG cannot be given (genuinely unavailable, refused, or beyond 10 days), give oral aciclovir prophylaxis starting at day 7 after exposure and continuing to day 21 (day 28 if any immunoglobulin was given), at a prophylactic dose (for example 10 mg/kg four times daily, adjusted to renal function). Starting aciclovir immediately would be useless because the virus is not yet replicating, and stopping early leaves the late-incubation period uncovered.
- Observation alone is not acceptable in this child.
While waiting, record the exact exposure date and time in the notes - every subsequent decision is counted from that date - and check her varicella IgG if a result can be turned around quickly, since a positive result would change the plan.
2. How do you answer the two questions - should the steroid be stopped, and is it better to catch chickenpox now?
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Steroid question: do not stop the prednisolone abruptly. She has been on 2 mg/kg on alternate days for 11 weeks, which is long enough to suppress the hypothalamic-pituitary-adrenal axis; sudden withdrawal risks a nephrotic relapse and, less commonly, adrenal insufficiency. Continue the current dose and involve paediatric nephrology in any change. If she develops clinical chickenpox, the usual approach is to continue or even increase steroid cover during the acute illness in consultation with nephrology, because stress-dose coverage is needed, while treating the varicella aggressively. A reduction may be considered later, not as a prophylactic measure at exposure.
'Better to catch it now' question: explain why this is not a reasonable trade. In an immunosuppressed child, wild-type varicella can cause disseminated disease with pneumonitis, hepatitis, encephalitis and bacterial superinfection, and it can be fatal. It can also trigger a nephrotic relapse and interrupt months of school. The vaccine is available and is the safer way to acquire immunity - but it is a live vaccine and cannot be given to a child on this level of immunosuppression, and it is not a post-exposure measure in this situation. Address the mother's underlying wish (protection without repeated worry) by agreeing a plan: document the exposure, give prophylaxis, and once she is off steroids and in remission, discuss catch-up varicella vaccination with the nephrology team.
3. What do you tell the day unit and the family about surveillance, and what is the practical follow-up plan for the next 21 days?
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Incubation and surveillance: the incubation period is 10-21 days, so the relevant window is from 7 days after exposure (when she becomes infectious) to 21 days. Instruct the family to check the temperature twice daily and to look for spots, and to phone the unit the same day if either occurs - do not wait for the next appointment. Give written instructions on what a chickenpox rash looks like in the first 24 hours (macules and papules becoming vesicles) and warn that in a child on steroids the rash may be atypical or sparse at first.
Infection control actions: inform the unit's infection control team and the paediatric nephrology team today, document the exposure in the notes and on the unit's communicable disease log, and notify the family of the index case if contact tracing is being done. While potentially infectious (day 7 to 21), she should be kept away from pregnant staff and patients, neonates, and other immunosuppressed children; arrangements for the blood pressure check should be by phone or a home visit rather than the shared waiting room. The unit should review its own triage - a child with a fresh vesicular rash should not have been sitting in a general waiting area.
Follow-up plan: confirm the VZIG supply and the date it will be given; if it is given, start the surveillance clock again at the appropriate point and give aciclovir prophylaxis only if VZIG fails or is contraindicated. Book a telephone review at day 7, day 14 and day 21, with an open same-day review slot. If she develops chickenpox, she needs same-day assessment and intravenous aciclovir if she has any of: respiratory symptoms, abdominal pain, neurological signs, haemorrhagic rash, or continued new lesions after day 6 - and nephrology must be involved before any steroid adjustment.