Herpes Zoster - Epidemiology

Epidemiology

Varicella zoster virus (VZV) has a high level of infectivity and has a worldwide prevalence. Herpes zoster is a re-activation of latent VZV infection: this means that zoster can only occur in someone who has previously had chickenpox (varicella).

Herpes zoster has no relationship to season and does not occur in epidemics. There is, however, a strong relationship with increasing age. 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, and incidence rates worldwide are similar. This relationship with age has been demonstrated in many countries, and is attributed to the fact that cellular immunity declines as people grow older.

Another important risk factor is immunocompromise: HIV is an important example of immune compromise). Other risk factors include psychological stress. Blacks are at lower risk of shingles than caucasians. It is unclear whether the risk is increased in females. Other potential risk factors include mechanical trauma and exposure to immunotoxins.

There is no strong evidence for a genetic link or a link to family history. A 2008 study showed that people with close relatives who have had shingles are twice as likely to develop it themselves, but a 2010 study found no such link.

Adults with latent VZV infection who are exposed intermittently to children with chickenpox receive an immune boost. This periodic boost to the immune system helps to prevent shingles in older adults. When routine chickenpox vaccination was introduced in the US, the concern was that because older adults would no longer receive this natural, periodic boost, this would result in an increase in the incidence of shingles in the US.

Multiple studies and surveillance data, at least when viewed superficially, demonstrate no consistent trends in incidence in the U.S. since the chickenpox vaccination program began in 1995. However, upon closer inspection, the two studies that showed no increase in shingles incidence were conducted among populations where varicella vaccination was not as yet widespread in the community. A recent study by Patel et al. concluded that since the introduction of the chickenpox vaccine, hospitalization costs for complications of shingles have increased by more than $700 million annually for those over 60 years. Another study by Yih et al. reported that as varicella vaccine coverage in children increased, the incidence of varicella decreased and the occurrence of shingles among adults increased 90%. The results of a further study by Yawn et al. showed a 28% increase in shingles incidence from 1996 to 2001. 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.