Chicken Pox

Aetiology and epidemiology

Chicken pox is a common highly infectious illness found worldwide.

It is caused by the varicella zoster virus and is spread via respiratory droplets.

The incubation period for chicken pox is usually 10-21 days. The infectivity period starts when symptoms first appear and lasts until all the lesions have crusted over. This is usually around 5-6 days after the onset of the illness, with most crusts disappearing by 20 days.

Clinical assessment

Chicken pox is a coryzal-type illness with itchy fluid filled vesicles, which progress over the trunk around 3-5 days. It is possible to be infected with no symptoms. Fever tends to resolve by day 4.

Investigations

Chicken pox is a very common illness and the vast majority of cases can be managed symptomatically at home.

Prolonged fever >4 days should prompt the suspicion of complications of varicella such as secondary bacterial sepsis.

Under these circumstances, patients should be examined carefully with appropriate blood test work up and a chest x-ray, depending on their clinical presentation.

Management

Oral acyclovir has been shown to reduce the effects of chicken pox, for example the number of lesions and duration of fever, if used within 24 hours of the onset of rash in immunocompetent children.

Oral acylovir has not been shown to reduce the incidence of varicella zoster virus pneumonia or other complications when compared to placebo. Cochrane results do not support the widespread use of acyclovir in immunocompetent children [7].

Varicella zoster immunoglobulin (VZIG) should be given to neonates whose mothers develop the rash 7 days before or 7 days after the delivery, to reduce the risk of severe neonatal varicella.

Complications

Problems may arise where there is a failure to recognise the complications of secondary streptococcal or staphylococcal infections or to appropriately manage high-risk groups.

A prolonged fever for more than 4 days in a child with chicken pox, for example, should prompt the suspicion of secondary bacterial complications [8].

A range of complications including pneumonia, bacteraemia and encephalitis are recognised [9]. Neurological complications may occur without a preceding rash [10].

The incidence of congenital varicella syndrome is low if maternal infection occurs before 20 weeks of gestation. Congenital varicella syndrome is associated with shortened limbs, skin scarring, cataracts and growth retardation.

Ibuprofen should not be used for fever control with chicken pox due to the established risk of developing necrotising fascitis.