Varicella-zoster: reactivation or reinfection?

Postexposure Prophylaxis Against Varicella-Zoster Virus Infection Among Recipients of Hematopoietic Stem Cell Transplant: Unresolved Issues

Recent guidelines for the prevention of opportunistic infections have addressed a variety of issues germane to recipients of hematopoietic stem cell transplant. However, there are several issues regarding postexposure prophylaxis against varicella-zoster virus that remain unresolved. We address these questions and offer several consensus recommendations.

Pox in the docks: varicella outbreak in an Australian prison system

OBJECTIVES

1. Describe an outbreak of varicella in a prison system. 2. Highlight the risks of disease transmission within the prison environment. 3. Promote infection control guidelines for high-risk sub-groups within the prison system, including the application of quarantine.

SETTING

Four prisons, one prison hospital, the prison transport system, one courthouse.

MAIN OUTCOME MEASURES

Number of cases of varicella infection; reported varicella immunity status of cases and contacts; immunity status of known HIV antibody positive inmates.

RESULTS

Five cases of chickenpox were identified. There were 23 contacts of the Index Case occurring during transport between prison and court and whilst being held in the court holding cells. Two of these contacts developed chickenpox despite having given a prior history of infection. There were over 300 inmates exposed to varicella zoster virus (VZV) during the outbreak, including one HIV antibody positive inmate who had serologically confirmed immunity. This inmate developed shingles following exposure to VZV from one of the cases.

CONCLUSIONS

There is an elevated risk of respiratory transmission of infections such as chickenpox in prisons. Clear guidelines should be in place to protect HIV antibody positive people, pregnant women, and others who are at increased risk of complications from such infections. In the case of varicella, all inmates and staff without documented immunity should be screened to determine immunity, and if non-immune, should be offered VZV vaccination. Every effort should be made to prevent HIV antibody positive inmates being exposed to varicella, regardless of their varicella immunity status. If an HIV antibody positive inmate, who is known to be non-immune is exposed to varicella, Varicella Zoster immunoglobulin should be given within 96 h.

The epidemiology of varicella-zoster virus infections: the influence of varicella on the prevalence of herpes zoster

This paper uses mathematical models and data analysis to examine the epidemiological implications of possible immunologically mediated links between patterns of varicella and herpes-zoster incidence in human communities. A review of previously published reports does not clarify whether or not there is a relationship between the incidence of varicella and the incidence of zoster. However, new analysis of data collected by the Royal College of General Practitioners provides indirect evidence for the hypothesis that a high intensity of varicella transmission suppresses viral reactivation. The significance of this finding for proposed varicella vaccination campaigns is explored by a review of published data on the use of the vaccine. No significant difference is shown to exist between the risk of zoster caused by the vaccine and the wild virus. A mathematical model is then developed to take into consideration the influence of the prevalence of varicella on viral reactivation and the impact of vaccination with attenuated virus, which may be able to recrudesce. Under some conditions, mass application of such vaccines may have the impact of increasing zoster incidence. The results presented here indicate that, before starting any vaccination programme against varicella, its consequences need to be assessed in much more depth.

The epidemiology of varicella-zoster virus infections: a mathematical model

Herpes-zoster is caused by the reactivation of varicella-zoster virus (VZV). In this paper different hypotheses of how this re-emergence of virus comes about are reviewed and discussed. From these hypotheses, and epidemiological data describing the initial transmission of the virus, a mathematical model of primary disease (varicella) and reactivated disease (zoster) in developed countries is derived. The steady-state age distributions of zoster cases predicted by this model are compared with the observed distribution, derived from a review and analysis of published epidemiological data. The model allows differentiation between published hypotheses in which age of host may or may not influence the probability of viral reactivation. The results indicate that the probability of reactivation must increase with age to allow the observed pattern of zoster cases. The basic mathematical model presented provides a conceptual framework, which may be extended to assess possible control programmes.

The epidemiology of herpes zoster

The epidemiology of Zoster is analysed by means of data acquired from the Zoster Clinic at Moorfields and the RCGP Research Unit. It complements and extends previous surveys, using much larger and consistent data, showing the effects of age, sex and season. The behaviour in the population as a whole and the pathogenesis are discussed; a model is proposed to explain the characteristics of some of the data, particularly the effects of age and non-specific stresses.