Varicella zoster virus (VZV) has a high level of infectivity and has a worldwide prevalence.<unk>  is a re-activation of latent VZV infection: zoster can only occur in someone who has previously had chickenpox (varicella).<unk>  has no relationship to season and does not occur in epidemics. There is, however, a strong relationship with increasing age. The incidence rate of<unk>  ranges from 1.2 to 3.4 per 1,000 person‐years among younger 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 immunosuppression. Other risk factors include psychological stress. According to a study in North Carolina, "black subjects were significantly less likely to develop zoster than were white subjects." It is unclear whether the risk is different by sex. 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 had<unk>  were 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<unk>  in older adults. When routine chickenpox vaccination was introduced in the United States, there was concern that, because older adults would no longer receive this natural periodic boost, there would be an increase in the incidence of<unk> . 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<unk>  incidence were conducted among populations where varicella vaccination was not as yet widespread in the community. A later study by Patel et al. concluded that since the introduction of the chickenpox vaccine, hospitalization costs for complications of<unk>  increased by more than $700 million annually for those over age 60. Another study by Yih et al. reported that as varicella vaccine coverage in children increased, the incidence of varicella decreased, and the occurrence of<unk>  among adults increased by 90%. The results of a further study by Yawn et al. showed a 28% increase in<unk>  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 those who contract<unk>  eventually present complications. Postherpetic neuralgia arises in approximately 20% of people with<unk> . 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.
Shingles
Insect bites and stings
Sealpox
Angina
Farmyard pox
Herpes simplex
Streptococcal intertrigo
Sciatica