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      Varicella and Herpes Zoster in Madrid, based on the Sentinel General Practitioner Network: 1997–2004

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          Abstract

          Background

          Varicella (chickenpox) is the primary disease caused by varicella-zoster virus. It is extremely contagious and is frequent in children. Indeed, in the absence of vaccination, a high proportion of the population is liable to contract it. Herpes zoster -more frequent among adults- is caused by reactivation of the latent virus. The objective of this study is to describe the status of and time trend for varicella and herpes zoster in the Madrid Autonomous Region prior to the introduction of the vaccine to the general population.

          Methods

          Data source: individualised varicella and herpes zoster case records kept by the Madrid Autonomous Region Sentinel General Practitioner Network for the period 1997–2004. Cumulative incidences, crude and standardised incidence rates, and age-specific rates of varicella and herpes zoster were calculated for each year. Kendall's Tau-b correlation coefficient was calculated to evaluate whether incidence displayed a time trend. Spectral density in the time series of weekly incidences was estimated using a periodogram.

          Results

          Standardised annual varicella incidence rates ranged from 742.5 (95% CI: 687.2 – 797.7) to 1239.6 (95% CI: 1164.5 – 1313.4) cases per 100 000 person-years. Most cases affected children, though complications were more frequent in adults. Varicella incidence displayed an annual periodicity but no trend over time. Most herpes zoster cases occurred at advanced ages, with incidence registering a rising annual trend but no seasonality factor.

          Conclusion

          In the absence of vaccination, no significant changes in varicella incidence were in evidence recent years, though these were observed in the incidence of herpes zoster. Sentinel general practitioner networks are a valid instrument for surveillance of diseases such as varicella. Further varicella vaccination-coverage and vaccine-efficacy studies are called for.

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          Most cited references30

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          What does epidemiology tell us about risk factors for herpes zoster?

          Reactivation of latent varicella zoster virus as herpes zoster is thought to result from waning of specific cell-mediated immunity, but little is known about its determinants in individuals with no underlying immunosuppression. We systematically reviewed studies of zoster epidemiology in adults and analysed data from a large morbidity study to identify factors that might be modulated to reduce the risk of zoster. Annual zoster incidence in population-based studies varied from 3.6-14.2/10(3) in the oldest individuals. Risk factors identified in analytical studies that could explain this variation included age, sex, ethnicity, genetic susceptibility, exogenous boosting of immunity from varicella contacts, underlying cell-mediated immune disorders, mechanical trauma, psychological stress, and immunotoxin exposure. Our review highlights the lack of information about risk factors for zoster. We suggest areas of research that could lead to interventions to limit the incidence of zoster. Such research might also help to identify risk factors for age-related immune decline.
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            The effectiveness of the varicella vaccine in clinical practice.

            A live attenuated varicella vaccine was approved for use in the United States in March 1995 and is recommended for all susceptible persons 12 months of age or older. To assess the effectiveness of the varicella vaccine, we conducted a case-control study with two controls per child with chickenpox, matched according to both age and pediatric practice. Children with potential cases of chickenpox were identified by active surveillance of pediatric practices in the New Haven, Connecticut, area. Research assistants visited the children on day 3, 4, or 5 of the illness, assessed the severity of the illness, and collected samples from lesions to test for varicella-zoster virus by polymerase chain reaction (PCR). From March 1997 through November 2000, data collection was completed for 330 potential cases, of which 243 (74 percent) were in children who had positive PCR tests for varicella-zoster virus. Of the 56 vaccinated children with chickenpox, 86 percent had mild disease, whereas only 48 percent of the 187 unvaccinated children with chickenpox had mild disease (P<0.001). Among the 202 children with PCR-confirmed varicella-zoster virus and their 389 matched controls, 23 percent of the children with chickenpox and 61 percent of the matched controls had received the vaccine (vaccine effectiveness, 85 percent; 95 percent confidence interval, 78 to 90 percent; P<0.001). Against moderately severe and severe disease the vaccine was 97 percent effective (95 percent confidence interval, 93 to 99 percent). The effectiveness of the vaccine was virtually unchanged (87 percent) after adjustment for potential confounders by means of conditional logistic regression. Varicella vaccine is highly effective as used in clinical practice.
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              Exposure to varicella boosts immunity to herpes-zoster: implications for mass vaccination against chickenpox.

              We present data to confirm that exposure to varicella boosts immunity to herpes-zoster. We show that exposure to varicella is greater in adults living with children and that this exposure is highly protective against zoster (Incidence ratio=0.75, 95% CI, 0.63-0.89). The data is used to parameterise a mathematical model of varicella zoster virus (VZV) transmission that captures differences in exposure to varicella in adults living with and without children. Under the 'best-fit' model, exposure to varicella is estimated to boost cell-mediated immunity for an average of 20 years (95% CI, 7-41years). Mass varicella vaccination is expected to cause a major epidemic of herpes-zoster, affecting more than 50% of those aged 10-44 years at the introduction of vaccination.
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                Author and article information

                Journal
                BMC Infect Dis
                BMC Infectious Diseases
                BioMed Central (London )
                1471-2334
                2007
                15 June 2007
                : 7
                : 59
                Affiliations
                [1 ]Department of Epidemiology, Madrid Public Health Institute, Julián Camarillo 4B, 28037 Madrid, Spain
                Article
                1471-2334-7-59
                10.1186/1471-2334-7-59
                1913920
                17570859
                184dae6e-989e-4ee5-ad23-e7302f08b00a
                Copyright © 2007 Pérez-Farinós et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 21 February 2007
                : 15 June 2007
                Categories
                Research Article

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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