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Li Y, Li J, Zhu Z, Zeng W, Zhu Q, Rong Z, Hu J, Li X, He G, Zhao J, Yin L, Quan Y, Zhang Q, Li M, Zhang L, Zhou Y, Liu T, Ma W, Zeng S, Chen Q, Sun L, Xiao J. Exposure-response relationship between temperature, relative humidity, and varicella: a multicity study in South China. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:7594-7604. [PMID: 36044136 DOI: 10.1007/s11356-022-22711-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 08/21/2022] [Indexed: 06/15/2023]
Abstract
Varicella is a rising public health issue. Several studies have tried to quantify the relationships between meteorological factors and varicella incidence but with inconsistent results. We aim to investigate the impact of temperature and relative humidity on varicella, and to further explore the effect modification of these relationships. In this study, the data of varicella and meteorological factors from 2011 to 2019 in 21 cities of Guangdong Province, China were collected. Distributed lag nonlinear models (DLNM) were constructed to explore the relationship between meteorological factors (temperature and relative humidity) and varicella in each city, controlling in school terms, holidays, seasonality, long-term trends, and day of week. Multivariate meta-analysis was applied to pool the city-specific estimations. And the meta-regression was used to explore the effect modification for the spatial heterogeneity of city-specific meteorological factors and social factors (such as disposable income per capita, vaccination coverage, and so on) on varicella. The results indicated that the relationship between temperature and varicella in 21 cities appeared nonlinear with an inverted S-shaped. The relative risk peaked at 20.8 ℃ (RR = 1.42, 95% CI: 1.22, 1.65). The relative humidity-varicella relationship was approximately L-shaped, with a peaking risk at 69.5% relative humidity (RR = 1.25, 95% CI: 1.04, 1.50). The spatial heterogeneity of temperature-varicella relationships may be caused by income or varicella vaccination coverage. And varicella vaccination coverage may contribute to the spatial heterogeneity of the relative humidity-varicella relationship. The findings can help us deepen the understanding of the meteorological factors-varicella association and provide evidence for developing prevention strategy for varicella epidemic.
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Affiliation(s)
- Yihan Li
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Jialing Li
- Institute of Immunization Program, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Zhihua Zhu
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Weilin Zeng
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Qi Zhu
- Institute of Immunization Program, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Zuhua Rong
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Jianxiong Hu
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Xing Li
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Guanhao He
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Jianguo Zhao
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Lihua Yin
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Yi Quan
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Qian Zhang
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Manman Li
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Li Zhang
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Yan Zhou
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Tao Liu
- Department of Public Health and Preventive Medicine, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Wenjun Ma
- Department of Public Health and Preventive Medicine, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Siqing Zeng
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Qing Chen
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China
| | - Limei Sun
- Institute of Immunization Program, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China
| | - Jianpeng Xiao
- School of Public Health, Southern Medical University, Guangzhou, 510515, Guangdong, China.
- Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, Guangdong, China.
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Inferring age-specific differences in susceptibility to and infectiousness upon SARS-CoV-2 infection based on Belgian social contact data. PLoS Comput Biol 2022; 18:e1009965. [PMID: 35353810 PMCID: PMC9000131 DOI: 10.1371/journal.pcbi.1009965] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 04/11/2022] [Accepted: 02/24/2022] [Indexed: 11/19/2022] Open
Abstract
Several important aspects related to SARS-CoV-2 transmission are not well known due to a lack of appropriate data. However, mathematical and computational tools can be used to extract part of this information from the available data, like some hidden age-related characteristics. In this paper, we present a method to investigate age-specific differences in transmission parameters related to susceptibility to and infectiousness upon contracting SARS-CoV-2 infection. More specifically, we use panel-based social contact data from diary-based surveys conducted in Belgium combined with the next generation principle to infer the relative incidence and we compare this to real-life incidence data. Comparing these two allows for the estimation of age-specific transmission parameters. Our analysis implies the susceptibility in children to be around half of the susceptibility in adults, and even lower for very young children (preschooler). However, the probability of adults and the elderly to contract the infection is decreasing throughout the vaccination campaign, thereby modifying the picture over time.
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Estimates of the basic reproduction number for rubella using seroprevalence data and indicator-based approaches. PLoS Comput Biol 2022; 18:e1008858. [PMID: 35239641 PMCID: PMC8893344 DOI: 10.1371/journal.pcbi.1008858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 01/23/2022] [Indexed: 11/19/2022] Open
Abstract
The basic reproduction number (R0) of an infection determines the impact of its control. For many endemic infections, R0 is often estimated from appropriate country-specific seroprevalence data. Studies sometimes pool estimates from the same region for settings lacking seroprevalence data, but the reliability of this approach is unclear. Plausibly, indicator-based approaches could predict R0 for such settings. We calculated R0 for rubella for 98 settings and correlated its value against 66 demographic, economic, education, housing and health-related indicators. We also trained a random forest regression algorithm using these indicators as the input and R0 as the output. We used the mean-square error to compare the performances of the random forest, simple linear regression and a regional averaging method in predicting R0 using 4-fold cross validation. R0 was <5, 5–10 and >10 for 81, 14 and 3 settings respectively, with no apparent regional differences and in the limited available data, it was usually lower for rural than urban areas. R0 was most correlated with educational attainment, and household indicators for the Pearson and Spearman correlation coefficients respectively and with poverty-related indicators followed by the crude death rate considering the Maximum Information Coefficient, although the correlation for each was relatively weak (Pearson correlation coefficient: 0.4, 95%CI: (0.24,0.48) for educational attainment). A random forest did not perform better in predicting R0 than simple linear regression, depending on the subsets of training indicators and studies, and neither out-performed a regional averaging approach. R0 for rubella is typically low and using indicators to estimate its value is not straightforward. A regional averaging approach may provide as reliable an estimate of R0 for settings lacking seroprevalence data as one based on indicators. The findings may be relevant for other infections and studies estimating the disease burden and the impact of interventions for settings lacking seroprevalence data.
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Abrams S, Wambua J, Santermans E, Willem L, Kuylen E, Coletti P, Libin P, Faes C, Petrof O, Herzog SA, Beutels P, Hens N. Modelling the early phase of the Belgian COVID-19 epidemic using a stochastic compartmental model and studying its implied future trajectories. Epidemics 2021; 35:100449. [PMID: 33799289 PMCID: PMC7986325 DOI: 10.1016/j.epidem.2021.100449] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 02/09/2021] [Accepted: 03/04/2021] [Indexed: 02/08/2023] Open
Abstract
Following the onset of the ongoing COVID-19 pandemic throughout the world, a large fraction of the global population is or has been under strict measures of physical distancing and quarantine, with many countries being in partial or full lockdown. These measures are imposed in order to reduce the spread of the disease and to lift the pressure on healthcare systems. Estimating the impact of such interventions as well as monitoring the gradual relaxing of these stringent measures is quintessential to understand how resurgence of the COVID-19 epidemic can be controlled for in the future. In this paper we use a stochastic age-structured discrete time compartmental model to describe the transmission of COVID-19 in Belgium. Our model explicitly accounts for age-structure by integrating data on social contacts to (i) assess the impact of the lockdown as implemented on March 13, 2020 on the number of new hospitalizations in Belgium; (ii) conduct a scenario analysis estimating the impact of possible exit strategies on potential future COVID-19 waves. More specifically, the aforementioned model is fitted to hospital admission data, data on the daily number of COVID-19 deaths and serial serological survey data informing the (sero)prevalence of the disease in the population while relying on a Bayesian MCMC approach. Our age-structured stochastic model describes the observed outbreak data well, both in terms of hospitalizations as well as COVID-19 related deaths in the Belgian population. Despite an extensive exploration of various projections for the future course of the epidemic, based on the impact of adherence to measures of physical distancing and a potential increase in contacts as a result of the relaxation of the stringent lockdown measures, a lot of uncertainty remains about the evolution of the epidemic in the next months.
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Affiliation(s)
- Steven Abrams
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium; Global Health Institute, Family Medicine and Population Health, University of Antwerp, Antwerp, Belgium.
| | - James Wambua
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium
| | - Eva Santermans
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium
| | - Lander Willem
- Centre for Health Economic Research and Modelling Infectious Diseases, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
| | - Elise Kuylen
- Centre for Health Economic Research and Modelling Infectious Diseases, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
| | - Pietro Coletti
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium
| | - Pieter Libin
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium; Artificial Intelligence Lab, Department of Computer Science, Vrije Universiteit Brussel, Brussels, Belgium; Department of Microbiology and Immunology, Rega Institute for Medical Research, Clinical and Epidemiological Virology, University of Leuven, Leuven, Belgium
| | - Christel Faes
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium
| | - Oana Petrof
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium
| | - Sereina A Herzog
- Centre for Health Economic Research and Modelling Infectious Diseases, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
| | - Philippe Beutels
- Centre for Health Economic Research and Modelling Infectious Diseases, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
| | - Niel Hens
- Data Science Institute, Interuniversity Institute of Biostatistics and statistical Bioinformatics, UHasselt, Hasselt, Belgium; Centre for Health Economic Research and Modelling Infectious Diseases, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
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Todorova TT. Seasonal dynamics of varicella incidence in Bulgaria. Future Virol 2020. [DOI: 10.2217/fvl-2020-0012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aim: Spatial and temporal distribution of varicella is heterogenic and insufficiently studied in Europe. The present study tries to fill the gap that exists about the seasonality of the infection in Bulgaria. Materials & methods: A 4-year retrospective study of the monthly and seasonal varicella epidemiology was performed at both national and district level. Results: In Bulgaria, varicella incidence peaked during winter (37% of the 2015–2018 cases), followed by spring (33%) and autumn (23%). Highly populated districts were more likely to follow this pattern, while less inhabited districts with smaller urbanized areas showed different periodicity of the infection. Conclusion: Winter peak in varicella incidence is positively associated with high accumulation of people in the large cities (>75,000 inhabitants).
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Affiliation(s)
- Tatina T Todorova
- Department of Microbiology & Virology, Medical University Varna, Faculty of Medicine, Varna, Bulgaria
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Funk S, Knapp JK, Lebo E, Reef SE, Dabbagh AJ, Kretsinger K, Jit M, Edmunds WJ, Strebel PM. Combining serological and contact data to derive target immunity levels for achieving and maintaining measles elimination. BMC Med 2019; 17:180. [PMID: 31551070 PMCID: PMC6760101 DOI: 10.1186/s12916-019-1413-7] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 08/20/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Vaccination has reduced the global incidence of measles to the lowest rates in history. However, local interruption of measles virus transmission requires sustained high levels of population immunity that can be challenging to achieve and maintain. The herd immunity threshold for measles is typically stipulated at 90-95%. This figure does not easily translate into age-specific immunity levels required to interrupt transmission. Previous estimates of such levels were based on speculative contact patterns based on historical data from high-income countries. The aim of this study was to determine age-specific immunity levels that would ensure elimination of measles when taking into account empirically observed contact patterns. METHODS We combined estimated immunity levels from serological data in 17 countries with studies of age-specific mixing patterns to derive contact-adjusted immunity levels. We then compared these to case data from the 10 years following the seroprevalence studies to establish a contact-adjusted immunity threshold for elimination. We lastly combined a range of hypothetical immunity profiles with contact data from a wide range of socioeconomic and demographic settings to determine whether they would be sufficient for elimination. RESULTS We found that contact-adjusted immunity levels were able to predict whether countries would experience outbreaks in the decade following the serological studies in about 70% of countries. The corresponding threshold level of contact-adjusted immunity was found to be 93%, corresponding to an average basic reproduction number of approximately 14. Testing different scenarios of immunity with this threshold level using contact studies from around the world, we found that 95% immunity would have to be achieved by the age of five and maintained across older age groups to guarantee elimination. This reflects a greater level of immunity required in 5-9-year-olds than established previously. CONCLUSIONS The immunity levels we found necessary for measles elimination are higher than previous guidance. The importance of achieving high immunity levels in 5-9-year-olds presents both a challenge and an opportunity. While such high levels can be difficult to achieve, school entry provides an opportunity to ensure sufficient vaccination coverage. Combined with observations of contact patterns, further national and sub-national serological studies could serve to highlight key gaps in immunity that need to be filled in order to achieve national and regional measles elimination.
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Affiliation(s)
- Sebastian Funk
- Centre for the Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
| | - Jennifer K. Knapp
- Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA USA
| | - Emmaculate Lebo
- Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA USA
| | - Susan E. Reef
- Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA USA
| | - Alya J. Dabbagh
- World Health Organization, Avenue Appia 20, Geneva, Switzerland
| | | | - Mark Jit
- Centre for the Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
- Modelling and Economics Unit, National Infections Service, Public Health England, 61 Colindale Avenue, London, UK
- School of Public Health, University of Hong Kong, 7 Sassoon Road, Hong Kong SAR, China
| | - W. John Edmunds
- Centre for the Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
| | - Peter M. Strebel
- GAVI Alliance, Chemin du Pommier 40, Le Grand-Saconnex, Switzerland
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le Polain de Waroux O, Flasche S, Kucharski AJ, Langendorf C, Ndazima D, Mwanga-Amumpaire J, Grais RF, Cohuet S, Edmunds WJ. Identifying human encounters that shape the transmission of Streptococcus pneumoniae and other acute respiratory infections. Epidemics 2018; 25:72-79. [PMID: 30054196 PMCID: PMC6227246 DOI: 10.1016/j.epidem.2018.05.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 05/17/2018] [Accepted: 05/17/2018] [Indexed: 01/23/2023] Open
Abstract
Although patterns of social contacts are believed to be an important determinant of infectious disease transmission, it remains unclear how the frequency and nature of human interactions shape an individual's risk of infection. We analysed data on daily social encounters individually matched to data on S. pneumoniae carriage and acute respiratory symptoms (ARS), from 566 individuals who took part in a survey in South-West Uganda. We found that the frequency of physical (i.e. skin-to-skin), long (≥1 h) and household contacts - which capture some measure of close (i.e. relatively intimate) contact - was higher among pneumococcal carriers than non-carriers, and among people with ARS compared to those without, irrespective of their age. With each additional physical encounter the age-adjusted risk of carriage and ARS increased by 6% (95%CI 2-9%) and 7% (2-13%) respectively. In contrast, the number of casual contacts (<5 min long) was not associated with either pneumococcal carriage or ARS. A detailed analysis by age of contacts showed that the number of close contacts with young children (<5 years) was particularly higher among older children and adult carriers than non-carriers, while the higher number of contacts among people suffering from ARS was more homogeneous across contacts of all ages. Our findings provide key evidence that the frequency of close interpersonal contact is important for transmission of respiratory infections, but not that of casual contacts. Those results are essential for both improving disease prevention and control efforts as well as informing research on infectious disease dynamics and transmission models, and more studies should be undertaken to further validate our results.
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Affiliation(s)
- Olivier le Polain de Waroux
- Centre for the Mathematical Modelling of Infectious Diseases, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, United Kingdom.
| | - Stefan Flasche
- Centre for the Mathematical Modelling of Infectious Diseases, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, United Kingdom
| | - Adam J Kucharski
- Centre for the Mathematical Modelling of Infectious Diseases, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, United Kingdom
| | - Celine Langendorf
- Department of Research, Epicentre, 8 Rue Saint-Sabin, 75011, Paris, France
| | - Donny Ndazima
- Epicentre Mbarara Research Centre, PO Box 1956, Mbarara, Uganda
| | - Juliet Mwanga-Amumpaire
- Epicentre Mbarara Research Centre, PO Box 1956, Mbarara, Uganda; Mbarara Universityof Science and Technology, Mbarara University, PO Box 1410, Mbarara, Uganda
| | - Rebecca F Grais
- Department of Research, Epicentre, 8 Rue Saint-Sabin, 75011, Paris, France
| | - Sandra Cohuet
- Department of Field Epidemiology, Epicentre, 8 Rue Saint-Sabin, 75011, Paris, France
| | - W John Edmunds
- Centre for the Mathematical Modelling of Infectious Diseases, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, United Kingdom
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Marziano V, Poletti P, Béraud G, Boëlle PY, Merler S, Colizza V. Modeling the impact of changes in day-care contact patterns on the dynamics of varicella transmission in France between 1991 and 2015. PLoS Comput Biol 2018; 14:e1006334. [PMID: 30067732 PMCID: PMC6089450 DOI: 10.1371/journal.pcbi.1006334] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 08/13/2018] [Accepted: 06/27/2018] [Indexed: 11/18/2022] Open
Abstract
Annual incidence rates of varicella infection in the general population in France have been rather stable since 1991 when clinical surveillance started. Rates however show a statistically significant increase over time in children aged 0-3 years, and a decline in older individuals. A significant increase in day-care enrolment and structures' capacity in France was also observed in the last decade. In this work we investigate the potential interplay between an increase of contacts of young children possibly caused by earlier socialization in the community and varicella transmission dynamics. To this aim, we develop an age-structured mathematical model, informed with historical demographic data and contact matrix estimates in the country, accounting for longitudinal linear increase of early childhood contacts. While the reported overall varicella incidence is well reproduced independently of mixing variations, age-specific empirical trends are better captured by accounting for an increase in contacts among pre-school children in the last decades. We found that the varicella data are consistent with a 30% increase in the number of contacts at day-care facilities, which would imply a 50% growth in the contribution of 0-3y old children to overall yearly infections in 1991-2015. Our findings suggest that an earlier exposure to pathogens due to changes in day-care contact patterns, represents a plausible explanation for the epidemiological patterns observed in France. Obtained results suggest that considering temporal changes in social factors in addition to demographic ones is critical to correctly interpret varicella transmission dynamics.
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Affiliation(s)
- Valentina Marziano
- Center for Information Technology, Bruno Kessler Foundation, Trento, Italy
- * E-mail:
| | - Piero Poletti
- Center for Information Technology, Bruno Kessler Foundation, Trento, Italy
| | - Guillaume Béraud
- Médecine Interne et Maladies Infectieuses, Centre Hospitalier de Poitiers, Poitiers, France
- EA2694, Université Droit et Santé Lille 2, Lille, France
- Interuniversity Institute for Biostatistics and statistical Bioinformatics, Hasselt University, Hasselt, Belgium
| | - Pierre-Yves Boëlle
- INSERM, Sorbonne Université, Institut Pierre Louis d’Epidémiologie et de Santé Publique IPLESP, Paris, France
| | - Stefano Merler
- Center for Information Technology, Bruno Kessler Foundation, Trento, Italy
| | - Vittoria Colizza
- INSERM, Sorbonne Université, Institut Pierre Louis d’Epidémiologie et de Santé Publique IPLESP, Paris, France
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9
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Williams JR, Manfredi P, Melegaro A. The potential impact of the demographic transition in the Senegal-Gambia region of sub-Saharan Africa on the burden of infectious disease and its potential synergies with control programmes: the case of hepatitis B. BMC Med 2018; 16:118. [PMID: 30041645 PMCID: PMC6058373 DOI: 10.1186/s12916-018-1100-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 06/14/2018] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Sub-Saharan Africa (SSA) continues to suffer high communicable disease burdens as its demographic transition (DT) proceeds. Although the consequent changes in population structures influence age-specific contact patterns relevant for transmission, the age distribution of immunity, and the disease burden, investigation of the potential of DT to affect infectious disease epidemiology in regions of SSA has hitherto been overlooked. With a substantial disease burden and complex epidemiology, hepatitis B virus (HBV) represents a prime example of an infection whose epidemiology may be significantly influenced by the DT. METHODS An age-structured mathematical model for HBV in the Senegal and Gambia (SG) region was set within a demographic framework with varying vital rates mirroring the entire course of the DT there over 1850-2100, to investigate the effects of the DT on HBV epidemiology, with and without the combined action of vaccination. The model was run from its reconstructed ancien régime (old order) demo-epidemiologic equilibrium and calibrated against SG 1950 age-distribution estimates and Gambian pre-vaccination HBV age-prevalence data. RESULTS The model, which reproduced well demographic and HBV age-prevalence data, predicted a complex transition of HBV epidemiology over the course of the DT. This included a prolonged epoch of expansion alongside population growth and rejuvenation until 1990-2000, followed by a dramatic retreat, mainly reflecting projected fertility decline during the twenty-first century. This transitional pattern was mostly explained by the underlying demographically driven changes in horizontal transmission resulting from the changes in the age structure of the population. During 2000-2150 the HBV burden is predicted to decline by more than 70% even in the absence of vaccination. CONCLUSIONS Demographic change alone may strongly affect HBV disease burden and shape HBV endemicity. The onset of the demographically driven decline in HBV prevalence, aligned with the expansion of HBV vaccination, forms a synergy potentially boosting effectiveness of control. Such a synergy currently appears to be presenting a "window of opportunity" facilitating HBV elimination which it would be important to exploit and which underlines the importance of taking demographic change into account when assessing the potential longer term impact of vaccination and other control measures.
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Affiliation(s)
- John R Williams
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London, W2 1PG, UK.
| | - Piero Manfredi
- Dipartimento di Economia e Management, University of Pisa, via Ridolfi 10, 56124, Pisa, Italy
| | - Alessia Melegaro
- Dondena Centre for Research on Social Dynamics and Public Policy and Department of Social and Political Science, Bocconi University, Via Roentgen 1, 20136, Milan, Italy
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10
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Medić S, Katsilieris M, Lozanov-Crvenković Z, Siettos CI, Petrović V, Milošević V, Brkić S, Andrews N, Ubavić M, Anastassopoulou C. Varicella zoster virus transmission dynamics in Vojvodina, Serbia. PLoS One 2018; 13:e0193838. [PMID: 29505590 PMCID: PMC5837184 DOI: 10.1371/journal.pone.0193838] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 02/19/2018] [Indexed: 01/29/2023] Open
Abstract
This study aimed at establishing baseline key epidemiological parameters for varicella zoster virus (VZV) infection in Vojvodina, Serbia, with the ultimate goal to quantify the VZV transmission potential in the population. Seroprevalence data generated during the first large cross-sectional VZV serosurvey were modelled, using a two-tiered modelling approach to calculate age-specific forces of infection (FOI), the basic reproduction number (R0) and herd immunity threshold (H). Seroprevalence and modelling data were compared with corresponding pre-vaccination epidemiological parameters from 11 countries participating in the European Sero-Epidemiology Network 2 (ESEN2) project. Serbia fits into the general dynamic VZV transmission patterns in Europe in the pre-vaccine era, with estimated R0 = 4.12, (95% CI: 2.69–7.07) and H = 0.76 (95% CI: 0.63–0.86). The highest VZV transmission occurs among preschool children, as evidenced by the estimation of the highest FOI (0.22, 95% CI: 0.11–0.34) in the 0.5–4 age group, with a peak FOI of 0.25 at 2.23 years. Seroprevalence was consistently lower in 5–14 year-olds, resulting in considerable shares of VZV-susceptible adolescents (7.3%), and young adults (6%), resembling the situation in a minority of European countries. The obtained key epidemiological parameters showed most intense VZV transmission in preschool children aged <4 years, justifying the consideration of universal childhood immunization in the future. National immunization strategy should consider programs for VZV serologic screening and immunization of susceptible groups, including adolescents and women of reproductive age. This work is an important milestone towards the evaluation of varicella immunization policy options in Serbia.
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Affiliation(s)
- Snežana Medić
- Center for Disease Control and Prevention, Institute of Public Health of Vojvodina, Novi Sad, Serbia
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
- * E-mail:
| | - Michalis Katsilieris
- School of Applied Mathematics and Physical Sciences, National Tehnical University of Athens, Athens, Greece
| | - Zagorka Lozanov-Crvenković
- Department of Mathematics and Computer Science, Faculty of Science, University of Novi Sad, Novi Sad, Serbia
| | - Constantinos I. Siettos
- School of Applied Mathematics and Physical Sciences, National Tehnical University of Athens, Athens, Greece
| | - Vladimir Petrović
- Center for Disease Control and Prevention, Institute of Public Health of Vojvodina, Novi Sad, Serbia
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Vesna Milošević
- Center for Disease Control and Prevention, Institute of Public Health of Vojvodina, Novi Sad, Serbia
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Snežana Brkić
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
- Clinic for Infectious Diseases, Clinical Center of Vojvodina, Novi Sad, Serbia
| | - Nick Andrews
- Statistics, Modelling, and Economics Department, National Infections Services, Public Health England, London, United Kingdom
| | | | - Cleo Anastassopoulou
- Division of Genetics, Cell and Developmental Biology, Department of Biology, University of Patras, Patras, Greece
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11
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Varicella infection in a non-universally vaccinated population: Actual epidemiology in Bulgaria (2013-2015). J Infect Public Health 2017; 11:326-330. [PMID: 29017751 DOI: 10.1016/j.jiph.2017.09.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 08/23/2017] [Accepted: 09/09/2017] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Varicella is a common and usually mild disease but it has great importance in regard to general infectious morbidity. The current study aimed to characterize possible risk factors of varicella epidemiology in Bulgaria, a country where infection follows its natural epidemiological pattern as no mandatory or recommended vaccine is currently applied. METHODS Administrative regions of Bulgaria were used as units of observation and a set of sociodemographic and economic determinants, as well as geographic location (south or north) were tested for associations with the mean 3-year varicella incidence rates (2013-2015). RESULTS The proportion of urban population, proportion of females, number of health care units and proportion of urban population aged <10 years were the four sociodemographic variables most strongly and significantly correlated (p<0.05) with varicella frequency (Spearman's rank correlation coefficients of 0.62, 0.47, 0.43, and 0.38, respectively). After reducing the number of intercorrelated factors to a few principal components and accounting for confounders, the demographic component and geographic location remained most robustly associated with varicella incidence in Bulgaria (adjusted R2 of 0.51, p<0.001). CONCLUSIONS The results obtained identify important determinants in the local epidemiology of varicella and show that community characteristics should be considered, to improve our understanding of varicella distribution.
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A systematic review of varicella seroprevalence in European countries before universal childhood immunization: deriving incidence from seroprevalence data. Epidemiol Infect 2017; 145:2666-2677. [PMID: 28826422 PMCID: PMC5647669 DOI: 10.1017/s0950268817001546] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Surveillance systems for varicella in Europe are highly heterogeneous or completely absent. We estimated the varicella incidence based on seroprevalence data, as these data are largely available and not biased by under-reporting or underascertainment. We conducted a systematic literature search for varicella serological data in Europe prior to introduction of universal varicella immunization. Age-specific serological data were pooled by country and serological profiles estimated using the catalytic model with piecewise constant force of infection. From the estimated profiles, we derived the annual incidence of varicella infection (/100·000) for six age groups (<5, 5–9, 10–14, 15–19, 20–39 and 40–65 years). In total, 43 studies from 16 countries were identified. By the age of 15 years, over 90% of the population has been infected by varicella in all countries except for Greece (86·6%) and Italy (85·3%). Substantial variability across countries exists in the age-specific annual incidence of varicella primary infection among the <5 years old (from 7052 to 16 122 per 100 000) and 5–9 years old (from 3292 to 11 798 per 100 000). The apparent validity and robustness of our estimates highlight the importance of serological data for the characterization of varicella epidemiology, even in the absence of sampling or assay standardization.
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13
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Meszner Z, Molnar Z, Rampakakis E, Yang HK, Kuter BJ, Wolfson LJ. Economic burden of varicella in children 1-12 Years of age in Hungary, 2011-2015. BMC Infect Dis 2017; 17:495. [PMID: 28705150 PMCID: PMC5513371 DOI: 10.1186/s12879-017-2575-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 06/29/2017] [Indexed: 11/16/2022] Open
Abstract
Background Although live-attenuated varicella-zoster virus (VZV) vaccines have been proven to be safe and effective in preventing varicella and real-word evidence shows routine childhood immunization programs are effective in dramatically reducing varicella associated morbidity and mortality, varicella vaccine is not included in the National Immunization Program (NIP) in Hungary. The purpose of this study was to evaluate the clinical and economic burden associated with varicella in Hungary. Methods This was a multicenter, retrospective, chart review study of patients aged 1–12 years with a primary varicella diagnosis between 2011 and 2015. Healthcare resource utilization (HCRU) associated with varicella, unit costs, and work loss were used to estimate direct and indirect costs. All costs are presented in 2015 HUF / Euros (€). Results 156 children with varicella were included (75 outpatients, 81 inpatients), with a mean age of 4.4 (SD: 2.0) and 3.7 (SD: 2.1) years, respectively. One or more complications were reported by 12.0% of outpatients and 92.6% of inpatients, the most common being dehydration, skin and soft tissue infections, pneumonia, keratoconjunctivitis, and cerebellitis. HCRU estimates included use of over-the-counter (OTC) medications (96.0% outpatients, 53.1% inpatients), prescription medications (9.3% outpatients, 70.4% inpatients), tests/procedures (4.0% outpatients, 97.5% inpatients), and consultation with allied health professionals (2.7% outpatients, 30.9% inpatients). The average duration of hospital stay (inpatients) was 3.6 (95% CI: 3.2, 4.1) days. The total combined direct and indirect cost per varicella case was 228,146.7 Hungarian Forint (HUF)/€ 736.0 for inpatients and 49,790.6 HUF/€ 106.6 for outpatients. The overall annual cost of varicella in Hungary for children aged <15 years in 2015 was estimated at 1,903,332,524.3 HUF/ € 6,139,980.4. Conclusion Varicella is associated with substantial clinical burden in Hungary, resulting in the utilization of a significant amount of healthcare resources. These results support the need for routine vaccination of all healthy children to reduce the varicella-associated disease burden.
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Affiliation(s)
- Z Meszner
- St. László Hospital for Infectious Diseases, National Institute of Child Health, Budapest, Hungary
| | - Z Molnar
- National Center for Epidemiology, Budapest, Hungary
| | | | - H K Yang
- Merck & Co, Inc., Center for Observational and Real-World Evidence (CORE), MAILSTOP WP97-A243, 770 Sumneytown Pike, West Point, PA, 19486, USA
| | - B J Kuter
- Merck & Co, Inc., Center for Observational and Real-World Evidence (CORE), MAILSTOP WP97-A243, 770 Sumneytown Pike, West Point, PA, 19486, USA
| | - Lara J Wolfson
- Merck & Co, Inc., Center for Observational and Real-World Evidence (CORE), MAILSTOP WP97-A243, 770 Sumneytown Pike, West Point, PA, 19486, USA.
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14
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Riera-Montes M, Bollaerts K, Heininger U, Hens N, Gabutti G, Gil A, Nozad B, Mirinaviciute G, Flem E, Souverain A, Verstraeten T, Hartwig S. Estimation of the burden of varicella in Europe before the introduction of universal childhood immunization. BMC Infect Dis 2017; 17:353. [PMID: 28521810 PMCID: PMC5437534 DOI: 10.1186/s12879-017-2445-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 05/07/2017] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Varicella is generally considered a mild disease. Disease burden is not well known and country-level estimation is challenging. As varicella disease is not notifiable, notification criteria and rates vary between countries. In general, existing surveillance systems do not capture cases that do not seek medical care, and most are affected by underreporting and underascertainment. We aimed to estimate the overall varicella disease burden in Europe to provide critical information to support decision-making regarding varicella vaccination. METHODS We conducted a systematic literature review to identify all available epidemiological data on varicella IgG antibody seroprevalence, primary care and hospitalisation incidence, and mortality. We then developed methods to estimate age-specific varicella incidence and annual number of cases by different levels of severity (cases in the community, health care seekers in primary care and hospitals, and deaths) for all countries belonging to the European Medicines Agency (EMA) region and Switzerland. RESULTS In the absence of universal varicella immunization, the burden of varicella would be substantial with a total of 5.5 million (95% CI: 4.7-6.4) varicella cases occurring annually across Europe. Variation exists between countries but overall the majority of cases (3 million; 95% CI: 2.7-3.3) would occur in children <5 years. Annually, 3-3.9 million patients would consult a primary care physician, 18,200-23,500 patients would be hospitalised, and 80 varicella-related deaths would occur (95% CI: 19-822). CONCLUSIONS Varicella disease burden is substantial. Most cases occur in children <5 years old but adults require hospitalisation more often and are at higher risk of death. This information should be considered when planning and evaluating varicella control strategies. A better understanding of the driving factors of country-specific differences in varicella transmission and health care utilization is needed. Improving and standardizing varicella surveillance in Europe, as initiated by the European Centre for Disease Prevention and Control (ECDC), is important to improve data quality to facilitate inter-country comparison.
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Affiliation(s)
- Margarita Riera-Montes
- P95 Pharmacovigilance and Epidemiology Services, Koning Leopold III Laan 1, 3001, Leuven, Belgium.
| | - Kaatje Bollaerts
- P95 Pharmacovigilance and Epidemiology Services, Koning Leopold III Laan 1, 3001, Leuven, Belgium
| | - Ulrich Heininger
- Division of Paediatric Infectious Diseases and Vaccinology, University of Basel Children's Hospital, CH-4056, Basel, Switzerland
| | - Niel Hens
- Interuniversity Institute for Biostatistics and statistical Bioinformatics, Hasselt University, Antwerp, Belgium.,Centre for Health Economics Research and Modelling Infectious Diseases and Centre for the Evaluation of Vaccination, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium
| | - Giovanni Gabutti
- Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Angel Gil
- Universidad Rey Juan Carlos, Madrid, Spain
| | - Bayad Nozad
- Department of Primary Care and Public Health, Imperial College London, London, UK
| | - Grazina Mirinaviciute
- Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Public Health, Oslo, Norway
| | - Elmira Flem
- Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Public Health, Oslo, Norway
| | | | - Thomas Verstraeten
- P95 Pharmacovigilance and Epidemiology Services, Koning Leopold III Laan 1, 3001, Leuven, Belgium
| | - Susanne Hartwig
- Sanofi Pasteur MSD, 162 avenue Jean Jaurès, 69007, Lyon, France
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15
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The natural history of varicella zoster virus infection in Norway: Further insights on exogenous boosting and progressive immunity to herpes zoster. PLoS One 2017; 12:e0176845. [PMID: 28545047 PMCID: PMC5436649 DOI: 10.1371/journal.pone.0176845] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 04/18/2017] [Indexed: 12/27/2022] Open
Abstract
We use age-structured models for VZV transmission and reactivation to reconstruct the natural history of VZV in Norway based on available pre-vaccination serological data, contact matrices, and herpes zoster incidence data. Depending on the hypotheses on contact and transmission patterns, the basic reproduction number of varicella in Norway ranges between 3.7 and 5.0, implying a vaccine coverage between 73 and 80% to effectively interrupt transmission with a 100% vaccine efficacy against infection. The varicella force of infection peaks during early childhood (3–5 yrs) and shows a prolonged phase of higher risk during the childbearing period, though quantitative variations can occur depending on contact patterns. By expressing the magnitude of exogenous boosting as a proportion of the force of infection, it is shown that reactivation is well described by a progressive immunity mechanism sustained by a large, though possibly below 100%, degree of exogenous boosting, in agreement with findings from other Nordic countries, implying large reproduction numbers of boosting. Moreover, magnitudes of exogenous boosting below 40% are robustly disconfirmed by data. These results bring further insight on the magnitude of immunity boosting and its relationship with reactivation.
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16
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Squamous epitheliotropism of Enterovirus A71 in human epidermis and oral mucosa. Sci Rep 2017; 7:45069. [PMID: 28322333 PMCID: PMC5359612 DOI: 10.1038/srep45069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 02/16/2017] [Indexed: 12/31/2022] Open
Abstract
Hand-foot-and-mouth disease is a self-limiting paediatric infectious disease commonly caused by Enterovirus A71 (Genus: Enterovirus, Family: Picornaviridae). Typical lesions in and around the hands, feet, oral cavity and other places may rarely be complicated by acute flaccid paralysis and acute encephalomyelitis. Although virus is readily cultured from skin vesicles and oral secretions, the cellular target/s of Enterovirus A71 in human skin and oral mucosa are unknown. In Enterovirus A71-infected human skin and oral mucosa organotypic cultures derived from the prepuce and lip biopsies, focal viral antigens and viral RNA were localized to cytoplasm of epidermal and mucosal squamous cells as early as 2 days post-infection. Viral antigens/RNA were associated with cytoplasmic vacuolation and cellular necrosis. Infected primary prepuce epidermal keratinocyte cultures showed cytopathic effects with concomitant detection of viral antigens from 2 days post-infection. Supernatant and/or tissue homogenates from prepuce skin organotypic cultures and primary prepuce keratinocyte cultures showed viral titres consistent with active viral replication. Our data strongly support Enterovirus A71 squamous epitheliotropism in the human epidermis and oral mucosa, and suggest that these organs are important primary and/or secondary viral replication sites that contribute significantly to oral and cutaneous viral shedding resulting in person-to-person transmission, and viraemia, which could lead to neuroinvasion.
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17
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The economic impact of prenatal varicella immunity among pregnant women in Alberta. Vaccine 2017; 35:570-576. [DOI: 10.1016/j.vaccine.2016.12.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Revised: 12/08/2016] [Accepted: 12/09/2016] [Indexed: 02/04/2023]
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18
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Del Fava E, Rimseliene G, Flem E, Freiesleben de Blasio B, Scalia Tomba G, Manfredi P. Estimating Age-Specific Immunity and Force of Infection of Varicella Zoster Virus in Norway Using Mixture Models. PLoS One 2016; 11:e0163636. [PMID: 27689800 PMCID: PMC5045180 DOI: 10.1371/journal.pone.0163636] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 09/12/2016] [Indexed: 01/28/2023] Open
Abstract
This study applies mixture modelling to examine age-specific immunity to varicella zoster virus (VZV) infection in Norway based on the first large-scale serological study in the general population. We estimated the seropositive proportions at different ages and calculated the underlying force of infection by using a sample of 2103 residual sera obtained from patients seeking primary and hospital care. A rapid increase in the VZV-associated immunity is observed in the first years of life with 63% of children being immune by age 5. The increase in the immunity levels slows down thereafter, with a large proportion of adults still susceptible by age 20 (around 14.5%), thus at risk of serious sequelae of varicella infection. The corresponding force of infection peaks during the preschool period, subsequently declines to a minimum between ages 10 and 20 years, and afterwards moderately increases to reach a plateau lasting throughout the childbearing period. In comparison with the traditional cut-off approach, mixture modelling used the whole data without producing any inconclusive cases, led to an unbiased classification of individuals between susceptible and immune, and provided a smoother immune profile by age. These findings represent an important step towards any decision about the introduction of varicella vaccination in Norway, as they are a primary input for mathematical transmission models aimed at evaluating potential vaccination scenarios.
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Affiliation(s)
- Emanuele Del Fava
- Carlo F. Dondena Centre for Research on Social Dynamics and Public Policy, Bocconi University, Milan, Italy
- * E-mail:
| | - Grazina Rimseliene
- Department of Vaccines, Norwegian Institute of Public Health, Oslo, Norway
| | - Elmira Flem
- Department of Vaccines, Norwegian Institute of Public Health, Oslo, Norway
| | - Birgitte Freiesleben de Blasio
- Oslo Centre for Biostatistics and Epidemiology, University of Oslo, Oslo, Norway
- Department of Infectious Disease Epidemiology, Norwegian Institute of Public Health, Oslo, Norway
| | | | - Piero Manfredi
- Department of Economics and Management, University of Pisa, Pisa, Italy
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19
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Xiao X, van Hoek AJ, Kenward MG, Melegaro A, Jit M. Clustering of contacts relevant to the spread of infectious disease. Epidemics 2016; 17:1-9. [PMID: 27639116 DOI: 10.1016/j.epidem.2016.08.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Revised: 08/04/2016] [Accepted: 08/23/2016] [Indexed: 10/21/2022] Open
Abstract
OBJECTIVE Infectious disease spread depends on contact rates between infectious and susceptible individuals. Transmission models are commonly informed using empirically collected contact data, but the relevance of different contact types to transmission is still not well understood. Some studies select contacts based on a single characteristic such as proximity (physical/non-physical), location, duration or frequency. This study aimed to explore whether clusters of contacts similar to each other across multiple characteristics could better explain disease transmission. METHODS Individual contact data from the POLYMOD survey in Poland, Great Britain, Belgium, Finland and Italy were grouped into clusters by the k medoids clustering algorithm with a Manhattan distance metric to stratify contacts using all four characteristics. Contact clusters were then used to fit a transmission model to sero-epidemiological data for varicella-zoster virus (VZV) in each country. RESULTS AND DISCUSSION Across the five countries, 9-15 clusters were found to optimise both quality of clustering (measured using average silhouette width) and quality of fit (measured using several information criteria). Of these, 2-3 clusters were most relevant to VZV transmission, characterised by (i) 1-2 clusters of age-assortative contacts in schools, (ii) a cluster of less age-assortative contacts in non-school settings. Quality of fit was similar to using contacts stratified by a single characteristic, providing validation that single stratifications are appropriate. However, using clustering to stratify contacts using multiple characteristics provided insight into the structures underlying infection transmission, particularly the role of age-assortative contacts, involving school age children, for VZV transmission between households.
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Affiliation(s)
- Xiong Xiao
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom; Department of Epidemiology and Biostatistics, West China School of Public Health, Sichuan University, Chengdu, China.
| | - Albert Jan van Hoek
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom.
| | - Michael G Kenward
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom.
| | - Alessia Melegaro
- DONDENA Centre for Research on Social Dynamics & Public Policy, Università Bocconi, Via Guglielmo Röntgen n. 1, 20136 Milan, Italy.
| | - Mark Jit
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom; Modelling and Economics Unit, Public Health England, 61 Colindale Avenue, London NW9 5EQ, United Kingdom.
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