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A 12-year-old girl presents with a 3-day history of an extensive vesicular and pruritic rash (Figure 129-1). The episode started 24 hours before the rash with fever and malaise. The patient is diagnosed with varicella, and no antiviral medications are given. Acetaminophen and/or ibuprofen are recommended for fever and discomfort.

FIGURE 129-1

Chickenpox in a child. Note lesions in various stages (papules, intact vesicles, pustules, and crusted papules) caused by multiple crops of lesions. The vesicles are on a red base. (Reproduced with permission from Richard P. Usatine, MD.)


Primary varicella, commonly known as chickenpox, is a highly contagious viral infection characterized by a distinctive rash with the potential to cause serious acute illness and to manifest later as zoster. The epidemiology of chickenpox has changed markedly since 1995 in the United States and other countries with high varicella vaccine coverage.


  • Varicella-zoster virus (VZV) is distributed worldwide. Humans are the only natural reservoir.

  • Incidence is seasonal, except in tropical climates, with most cases occurring during the winter and early spring. Peak incidence in the United States is between March and May.1

United States epidemiology before the vaccination program:

  • Estimated incidence of about 4 million/year.

  • Essentially everyone acquired varicella before adulthood, most as young children (Figure 129-2).

  • Most experienced the illness as a painful but benign and self-limited rash.

  • Household infection rate was more than 90% of susceptible individuals1 (Figure 129-3).

  • Complications from varicella accounted for approximately 11,000 hospital admission and 100 deaths annually.1

  • Complications were more prevalent in babies, older adults, and immunocompromised persons; most deaths actually occurred in immunocompetent children and adults.

FIGURE 129-2

Chickenpox in a child. Note the widespread distribution of the lesions. The honey-crusted lesion on the eyebrow suggests a secondary bacterial infection (impetigo). (Reproduced with permission from Richard P. Usatine, MD.)

FIGURE 129-3

Chickenpox in sisters seen before the varicella vaccine was available. The girls are feeling better now that the disease is resolving. (Reproduced with permission from Richard P. Usatine, MD.)

United States epidemiology since the vaccination program:

  • The incidence of chicken pox abruptly declined by 97%.

  • A high percentage of remaining cases are breakthrough varicella (infection with wild-type VZV more than 42 days after vaccination).1

  • Complications, including death, also declined dramatically—especially in children and young adults, where it decreased by 99%.2

  • Current groups vulnerable to morbidity and mortality include2,3:

    • Persons living with natural and/or medically induced immunodeficiency

    • Susceptible immigrants from the tropics

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