Herpes zoster epidemiology and demographics


 * L. Katie Morrison, MD; Associate Editor(s)-In-Chief:

Epidemiology and Demographics
Before introduction of varicella vaccine in the United States in 1995, varicella was endemic, with virtually all persons being infected by adulthood. Since implementation of the varicella vaccination program, incidence has declined in all age groups, with the greatest decline among children aged 1-4 years. Data from passive and active surveillance have indicated a decline in varicella cases of 70%-84% from 1995 through 2001 (1-3). The downward trend in varicella has continued in the United States through 2005 with an approximately 90% decline in incidence from 1995 in active surveillance sites with high vaccine coverage (CDC, unpublished data).

Varicella zoster virus has a high level of infectivity and is prevalent worldwide, and has a very stable prevalence from generation to generation. VZV is a benign disease in a healthy child in developed countries. However, varicella can be lethal to individuals who are infected later in life or who have low immunity. The number of people in this high-risk group has increased, due to the HIV epidemic and the increase in immunosuppressive therapies. Infections of varicella in institutions such as hospitals are also a significant problem, especially in hospitals that care for these high-risk populations.

In general, herpes zoster has no seasonal incidence and does not occur in epidemics. In temperate zones chickenpox is a disease of children, with most cases occurring during the winter and spring, most likely due to school contact; there is no evidence for regular epidemics. In the tropics chickenpox typically occurs among older people. Incidence is highest in people who are over age 55, as well as in immunocompromised patients regardless of age group, and in individuals undergoing psychological stress. Non-whites may be at lower risk; it is unclear whether the risk is increased in females. Other potential risk factors include mechanical trauma, genetic susceptibility, and exposure to immunotoxins.

The incidence rate of herpes zoster ranges from 1.2 to 3.4 per 1,000 person-years among healthy individuals, increasing to 3.9–11.8 per 1,000 person‐years among those older than 65 years. Similar incidence rates have been observed worldwide. Herpes zoster develops in an estimated 500,000 Americans each year. Multiple studies and surveillance data demonstrate no consistent trends in incidence in the U.S. since the chickenpox vaccination program began in 1995. It is likely that incidence rate will change in the future, due to the aging of the population, changes in therapy for malignant and autoimmune diseases, and changes in chickenpox vaccination rates; a wide adoption of zoster vaccination could dramatically reduce the incidence rate.

In one study, it was estimated that 26% of patients who contract herpes zoster eventually present with complications. Postherpetic neuralgia arises in approximately 20% of patients. A study of 1994 California data found hospitalization rates of 2.1 per 100,000 person-years, rising to 9.3 per 100,000 person-years for ages 60 and up. An earlier Connecticut study found a higher hospitalization rate; the difference may be due to the prevalence of HIV in the earlier study, or to the introduction of antivirals in California before 1994.