Varicella is normally acquired through contact with a patient with chickenpox (or, less frequently, direct contact with herpes zoster), so many patients have a history of such exposure. Exposure among children often takes place in the home, school, or day-care environments. Varicella is contagious with an attack rate of up to 90% in susceptible household members, but attack rates appear to be lower in classroom or day-care environments.[56] A prior history of chickenpox should be ascertained; 4.5% to 13.3% of people with varicella infection report previous varicella.[57] It is also important to review prior immunisation with varicella vaccine. Patients (or parents) may recall a prodrome consisting of fever, fatigue, headache, and/or sore throat, prior to the onset of the rash.

In healthy children, the disease is generally mild and self-limiting, with malaise, pruritus (itching), and temperature up to 39°C (102°F) for 2 to 3 days. However, some patient groups are at risk of severe disease and complications such as pneumonia, neurological sequelae, hepatitis, secondary bacterial infection, and even death. Secondary bacterial infection should be considered in patients with persistent (i.e., >3 days) or recurrent fever.

Children and adults with known immunosuppression, such as caused by malignancy, immunodeficiency, organ transplantation, HIV infection, or corticosteroid use, are at greater risk for complications from varicella infection.[58][59][60] Immunosuppressed patients are more likely to have organ involvement, pneumonia, and haemorrhagic skin disease. While patients with underlying malignancy represent a small number of total varicella events, they account for a large proportion of deaths (up to 50%).[61] In children receiving cancer chemotherapy, 7% of patients died due to primary varicella.[62] Data on immunosuppressed adults is more difficult to ascertain due to the lower incidence of adult varicella, but case reports indicate that these patients are also at greater risk for major complications.[63] In addition, women who develop varicella from 5 days to 2 days prior to delivery have a high risk (17% to 30%) of transmitting the virus to their newborn. Because of the absence of maternal immunity to varicella-zoster virus (VZV), these children are at risk for severe infection.[2]

Patients at moderate risk of severe disease include those:[1]

  • 13 years of age and over

  • With concurrent chronic skin disease (e.g., atopic dermatitis)

  • With concurrent underlying pulmonary disease

  • Receiving salicylate therapy

  • Receiving short-course or intermittent oral corticosteroids.

Patients at high risk of severe disease include:[2]

  • Immunocompromised patients (e.g., organ transplant, chemotherapy, HIV infection)

  • Neonates

  • Those taking chronic oral corticosteroids or high-dose systemic immunosuppressants

  • Pregnant women.

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