A pruritic rash in pregnancy
Jess, a 35-year-old woman, presents to her GP at 39+1 weeks’ gestation in her first pregnancy.
She complains of a widespread pruritic rash that started on the abdomen and back two days ago and has now spread to involve the arms, legs and face.
She has a one-day prodrome of fever and malaise.
She has no known direct contact with chickenpox. However, there have been a large number of cases of chickenpox in the community recently.
Jess is unsure whether she had chickenpox as a child. She has never received a varicella zoster virus (VZV) vaccination.
VZV IgG was undetected at seven weeks’ gestation. Jess asks if this could be chickenpox and is anxious about the potential impact of chickenpox on her fetus.
She has had an uncomplicated pregnancy to date and is planning to have a vaginal delivery.
Examination and investigation
On examination, there is a widespread vesicular rash with varying ages of maturity, characteristic of chickenpox. A few of the lesions on the trunk are beginning to crust.
The respiratory and abdominal examinations are normal. Full blood count and liver function tests are within normal limits. VZV IgG and IgM are not detected.
A PCR swab of the base of a de-roofed vesicle is positive for VZV DNA.
Jess’ GP urgently consults her obstetrician, who discusses her case with the local maternal-fetal medicine team.
They recommend oral valaciclovir 1g tds for seven days, with close follow-up in the community for any complications of varicella.
If Jess requires hospitalisation, she is to be managed in isolation with airborne precautions until all of her lesions are crusted.
If delivery occurs within seven days of the onset of chickenpox, it’s advised that the neonate should receive zoster immunoglobulin as soon as possible after birth, to prevent neonatal varicella infection.
Progress and follow-up
Jess develops mild nausea with valaciclovir, but is able to complete the course. Her lesions begin to resolve and heal with no signs of secondary bacterial infection. She remains systemically well.
Jess goes into spontaneous labour at 40+2 weeks’ gestation and proceeds to an uncomplicated vaginal delivery. The newborn boy has Apgar scores of 9 and 9.
Jess and her son are discharged three days later. Zoster immunoglobulin is not given to the newborn as he was delivered outside of the risk period for in-utero transmission causing neonatal varicella.
The diagnosis of chickenpox is primarily a clinical one.
It may be confused with polymorphic eruption of pregnancy, also known as pruritic urticarial papules and plaques of pregnancy (PEP or PUPP).
PEP is a common pruritic rash affecting 1 in every 160-300 pregnancies and classically occurring in the last weeks of a first pregnancy.
It particularly affects the abdominal striae, with periumbilical sparing, and evolves from erythematous papules to urticarial plaques.
If laboratory testing is required to confirm chickenpox, a PCR swab of the base of a de-roofed vesicle for VZV DNA is the test of choice.
In contrast, varicella IgM is liable to produce both false-negative and false-positive results. If serology is utilised, repeat convalescent testing to demonstrate IgG seroconversion is recommended.
There are two key considerations in the management of chickenpox in pregnancy.
First, like all adults, pregnant women are at higher risk of severe systemic complications of varicella, including pneumonia and neurological disease.
The Australian Therapeutic Guidelines recommends treating all pregnant women with uncomplicated varicella within the first 72 hours of the onset of rash, while some international guidelines recommend treatment of all cases regardless of time frame.
Complicated varicella infection (for example, pneumonia) requires admission and treatment with intravenous aciclovir.
Registry data has shown no increase in birth defects as a result of aciclovir use during pregnancy.
While valaciclovir, the prodrug of aciclovir, has less data to support safety in pregnancy, its use in this setting is widely accepted due to its considerably higher oral bioavailability and ease of dosing.
Non-immune pregnant women who have had significant contact with a case of chickenpox (for example, five minutes face-to-face or one hour in the same room) should be given passive immunisation with zoster immunoglobulin within 10 days of the exposure.
A history of immunity to varicella is established by either a personal history of chickenpox, documented age-appropriate vaccination or VZV IgG detected by serology.
Second, chickenpox can affect both the fetus and the newborn. Congenital varicella is uncommon, occurring maximally with exposure between 12 and 28 weeks’ gestation with an incidence of 1.5%.
Primary maternal varicella infection between seven days before and two days after delivery places the newborn at high risk of neonatal varicella, which has a case mortality of up to 30%.
This risk is significantly reduced or eliminated by passive immunisation with zoster immunoglobin given to the newborn as soon as possible after birth.
Dr Jim Newcombe is a paediatrician, infectious diseases physician and clinical microbiologist at Royal North Shore Hospital and Douglass Hanly Moir, Sydney, NSW.
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