Herpes zoster is a neurocutaneous disease that is caused by the reactivation of varicella-zoster virus (VZV) from a latent infection of dorsal sensory or cranial nerve ganglia following varicella or primary infection with VZV earlier in life. Herpes zoster is characterized by unilateral, dermatomal pain and rash.
Postherpetic neuralgia (PHN) has been defined as any pain after rash healing or any pain from 1 to 6 months after rash onset. Pain experts currently define PHN as pain 90 to 120 days after rash onset to be consistent with established definitions of chronic pain and to eliminate neuropathic pain from acute inflammation. Some experts define the herpes zoster pain trajectory as an acute herpetic neuralgia that lasts for approximately 30 days after rash onset, a subacute herpetic neuralgia that lasts from 30 to 120 days after rash onset, and PHN as pain that persists 120 days and more after rash onset.
Varicella-Zoster Virus Transmission
VZV is a double-stranded DNA that is transmitted from person to person via direct contact, airborne or droplet nuclei when a virus-naïve, VZV seronegative individual is exposed to the vesicular rash of varicella or herpes zoster. These exposed individuals may then develop varicella. Health care workers and staff in nursing homes and hospitals and children who have not received the varicella vaccine may not have had VZV primary infection and are potentially at risk for varicella. However, nearly all older adults are seropositive and latently infected with VZV. The exposure of a latently infected individual to herpes zoster does not cause herpes zoster or varicella. Furthermore, there is no risk of VZV transmission when the herpes zoster rash is only maculopapular or crusted. All cases of herpes zoster are caused by the reactivation of endogenous VZV.
Herpes Zoster Incidence and Risk Factors
In general population studies from North America and Europe, the incidence of herpes zoster in persons of all ages is 1.2 to 4.8 cases per 1000 persons per year and in persons older than 60 years old, the incidence is 7.2 to 11.8 cases per 1000 per year. The lifetime incidence of herpes zoster is estimated to be about 20% in the general population and maybe as high as 50% among those surviving to 85 years or higher.
The cardinal epidemiological feature of herpes zoster is its increase in incidence with aging and with diseases and drugs that impair cellular immunity. The increase in the likelihood of herpes zoster with aging starts around 50 to 60 years of age and increases into late life in individuals older than 80 years of age (Figure 129-1). In the herpes zoster vaccine trial (“Shingles Prevention Study”), which was prospective, used active surveillance in a community-based population, and used polymerase chain reaction (PCR) for definitive diagnosis of herpes zoster cases, the incidence of herpes zoster in the placebo group (n = 19 276) ...