ArticlesContacts with varicella or with children and protection against herpes zoster in adults: a case-control study
Introduction
Primary infection with varicella-zoster virus causes varicella, after which the virus establishes latency in dorsal root ganglia.1, 2, 3 Reactivation of latent infection is thought to result from declining specific cell-mediated immunity, and leads to herpes zoster.4, 5, 6 Zoster occurs frequently in ageing populations and causes substantial acute and chronic morbidity, the commonest long-term complication being persistent pain (post-herpetic neuralgia).7
Hope-Simpson postulated that exogenous exposure to people with varicella or zoster might boost specific immunity and therefore decrease the risk of zoster in latently infected individuals.8 Mothers of children with varicella have cell-mediated immune boosting, and children with leukaemia seem to be protected against zoster by household exposure to varicella.9, 10 However, whether exogenous exposure protects against zoster in immunocompetent adults is unclear. In one study, paediatricians had more contacts with patients infected with varicella-zoster virus than dermatologists or psychiatrists, and were significantly less likely to have developed zoster, but the results could have been influenced by very low response rates to the survey.11
The role of immune boosting is an important issue for varicella vaccination programmes, since a reduction in childhood varicella will result in fewer exogenous exposures to varicella-zoster virus, which could lead to increased incidence of zoster among unvaccinated adults.12 Varicella vaccination has already been introduced in countries such as the USA and Japan, and is being considered by many European countries. We therefore set up a study to test the hypothesis that exogenous exposure to varicella-zoster virus protects against zoster.
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Patients and controls
This investigation was one objective of a community-based case-control study of risk factors for zoster in immunocompetent adults in south London, UK, between September, 1997, and December, 1998. A reporting system was set up among 22 general practices to identify individuals who had recently been diagnosed with zoster by their family physician. For each patient with zoster, two controls with no history of zoster were sought by searching practice registers for individuals who were nearest in
Results
During the study period, 436 patients were identified, of whom 139 were ineligible (46 were younger than 16 years, 37 had recent immunosuppression, 18 were African, 11 were temporarily registered, four were incapable of answering questions, and 23 were identified more than 8 weeks after rash onset). Of the remaining 297 patients, 16 (5·4%) were not enrolled: 12 refused and four were away from London or repeatedly unavailable for more than 8 weeks. The eligibility of these patients was not
Discussion
The findings from this study suggest that continued exogenous exposure to varicella is protective against zoster in latently infected adults. This result is consistent with those of Gershon and colleagues,10 who found that vaccinated children with leukaemia were at significantly lower risk of zoster if they had household exposure to varicella, and that many of these children had evidence of immunological boosting. In our study, there were doseresponse effects associated with a range of
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