Piero Manfredi | University of Pisa (original) (raw)

Papers by Piero Manfredi

American Journal of Epidemiology, 2008

Social contact patterns are a critical explanatory factor of the spread of close-contact infectio... more Social contact patterns are a critical explanatory factor of the spread of close-contact infectious agents. Both indirect (via observed epidemiologic data) and direct (via diaries that record at-risk events) approaches to the measurement of contacts by age have been proposed in the literature. In this paper, the authors discuss the possibilities offered by time-use surveys to measure contact patterns and to explain observed seroprevalence profiles. The authors first develop a methodology to estimate time-of-exposure matrices, and then they apply it to time-use data for the United States (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). Finally, the authors estimate age-specific transmission parameters for varicella, commonly known as ''chickenpox,'' from age-specific time-of-exposure and seroprevalence data (United States, 1988-1994. The estimated time-of-exposure matrix reveals a strong element of assortativeness by age. In addition, there are peaks of exposure between people who were born one generation apart (i.e., parents and their children). Models based on the estimated age-specific transmission parameters fit the observed patterns of infection of endemically circulating varicella in a satisfactory way. The availability of time-use data for a large number of countries and their potential to supplement contact surveys make the methods developed extremely valuable and suitable for implementation in several different contexts.

Abstract Little is known on how different levels of population heterogeneity and different patter... more Abstract Little is known on how different levels of population heterogeneity and different patterns of human mobility affect the course of pandemic influenza in terms of timing and impact. By employing a large-scale spatially explicit individual-based model, founded on a highly detailed model of the European populations and on a careful analysis of air and railway transportation data, we provide quantitative measures of the influence of such factors at the European scale.

Background The 2009 H1N1 pandemic influenza dynamics in Italy was characterized by a notable patt... more Background The 2009 H1N1 pandemic influenza dynamics in Italy was characterized by a notable pattern: as it emerged from the analysis of influenza-like illness data, after an initial period (September–mid-October 2009) characterized by a slow exponential increase in the weekly incidence, a sudden and sharp increase of the growth rate was observed by mid-October. The aim here is to understand whether spontaneous behavioral changes in the population could be responsible for such a pattern of epidemic spread.

Riassunto: Il rischio di una pandemia influenzalee diventato piu sostanziale e persistente alla f... more Riassunto: Il rischio di una pandemia influenzalee diventato piu sostanziale e persistente alla fine del 2003, quando sie osservata una rapida crescita della diffusione del virus A (H5N1). In questo lavoro proponiamo un modello stocastico ad agenti individuali per verificare l'efficacia di alcune strategie di contenimento, quali vaccinazione, profilassi antivirale, misure per l'aumento della distanza sociale e limitazione dei voli aerei internazionali.

Beyond control measures imposed by public authorities, human behavioral changes can be triggered ... more Beyond control measures imposed by public authorities, human behavioral changes can be triggered by uncoordinated responses driven by the risk perception of an emerging epidemic. In order to account for spontaneous social distancing, a model based on an evolutionary game theory framework is here proposed. Behavioral changes are modeled through an imitation process in which the convenience of different behaviors depends on the perceived prevalence of infections.

SUMMARY We describe the real-time modelling analysis conducted in Italy during the early phases o... more SUMMARY We describe the real-time modelling analysis conducted in Italy during the early phases of the 2009 A/H1N1v influenza pandemic in order to estimate the impact of the pandemic and of the related mitigation measures implemented. Results are presented along with a comparison with epidemiological surveillance data which subsequently became available.

To investigate the 1918/19 influenza pandemic daily number of new hospitalizations in the only ho... more To investigate the 1918/19 influenza pandemic daily number of new hospitalizations in the only hospital in Florence (Central Italy) were analyzed. In order to describe the transmission dynamics of the 1918/1919 pandemic influenza a compartmental epidemic model was used. Model simulations show a high level of agreement with the observed epidemic data.

Evidence of preferential mixing through selected social routes has been suggested for the transmi... more Evidence of preferential mixing through selected social routes has been suggested for the transmission of tuberculosis (TB) infection in low burden settings. A realistic modelization of these contact routes is needed to appropriately assess the impact of individually targeted control strategies, such as contact network investigation of index cases and treatment of latent TB infection (LTBI).

We developed a stochastic individual-based discrete-time model to assess the impact of pandemic i... more We developed a stochastic individual-based discrete-time model to assess the impact of pandemic influenza containing strategies. The spread of influenza was then modeled with specific levels for households, schools/workplaces, and random contacts. We considered different R0 values (1.4, 1.7, 2), evaluating the impact of combined preventive measures (vaccination, antiviral prophylaxis (AVP), border restrictions and increased social distancing).

Viral hepatitis A, as other endemic diseases, represents a public health priority worldwide. To s... more Viral hepatitis A, as other endemic diseases, represents a public health priority worldwide. To study long-time scale human pathogens through individual-based simulations, the development of a dynamic network of contacts is required. In this work, we introduce an individual-based model accounting for the birth and death of the individuals, the generation of new households, and the educational career of the individuals, in order to investigate viral hepatitis A dynamics in the most affected Italian areas.

Influenza pandemics in the last century were characterized by successive waves and differences in... more Influenza pandemics in the last century were characterized by successive waves and differences in impact and timing between different regions, for reasons not clearly understood. The 2009 H1N1 pandemic showed rapid global spread, but with substantial heterogeneity in timing within each hemisphere.

Little is known on how different levels of population heterogeneity and different patterns of hum... more Little is known on how different levels of population heterogeneity and different patterns of human mobility would affect the course of an epidemic in terms of timing and impact. By employing a large-scale spatially-explicit individual-based model, based on a highly detailed model of the European populations and on a carefully analysis of air and railway transportation data, we provide quantitative measures of their effects at European level.

Background Individual based models have become a valuable tool for modeling the spatiotemporal dy... more Background Individual based models have become a valuable tool for modeling the spatiotemporal dynamics of epidemics, eg influenza pandemic, and for evaluating the effectiveness of intervention strategies. While specific contacts among individuals into diverse environments (family, school/workplace) can be modeled in a standard way by employing available socio-demographic data, all the other (unstructured) contacts can be dealt with by adopting very different approaches.

Abstract Botnets have become the most sophisticated and dangerous way of spreading malware. Their... more Abstract Botnets have become the most sophisticated and dangerous way of spreading malware. Their damaging actions can range from massive dispatching of e-mail messages, to denial of service attacks, to collection of private and sensitive information. Unlike standard computer viruses or worms, botnets spread silently without actively operating their damaging activity, and then are activated in a coordinated way to maximize the``benefit''of the malware.

Marburg hemorrhagic fever is rare yet among the most severe diseases affecting humans, with case ... more Marburg hemorrhagic fever is rare yet among the most severe diseases affecting humans, with case fatality ratio even higher than 80%. By analyzing the largest documented Marburg hemorrhagic fever epidemic, which occurred in Angola in 2005 and caused 329 deaths, and data on viral load over time in non-human primates, we make an assessment of transmissibility and severity of the disease. We also give insight into the control of new Marburg hemorrhagic fever epidemics to inform appropriate health responses.

We study how spontaneous reduction in the number of contacts could develop, as a defensive respon... more We study how spontaneous reduction in the number of contacts could develop, as a defensive response, during an epidemic and affect the course of infection events. A model is proposed which couples an SIR model with selection of behaviours driven by imitation dynamics. Therefore, infection transmission and population behaviour become dynamical variables that influence each other. In particular, time scales of behavioural changes and epidemic transmission can be different.

Mathematical models are powerful tools for simulating plausible epidemic spread scenarios and for... more Mathematical models are powerful tools for simulating plausible epidemic spread scenarios and for evaluating the impact of control policies. They represent the scientific basis on which public health policy makers should take their decisions on the intervention strategies that should be performed at local, national and international scale. In this context, Individual-Based simulation Models (IBM) have become one of the much relevant approaches.

During summer 2007 Italy has experienced an epidemic caused by Chikungunya virus–the first large ... more During summer 2007 Italy has experienced an epidemic caused by Chikungunya virus–the first large outbreak documented in a temperate climate country–with approximately 161 laboratory confirmed cases concentrated in two bordering villages in North–Eastern Italy comprising 3,968 inhabitants. The seroprevalence was recently estimated to be 10.2%.

American Journal of Epidemiology, 2008

Social contact patterns are a critical explanatory factor of the spread of close-contact infectio... more Social contact patterns are a critical explanatory factor of the spread of close-contact infectious agents. Both indirect (via observed epidemiologic data) and direct (via diaries that record at-risk events) approaches to the measurement of contacts by age have been proposed in the literature. In this paper, the authors discuss the possibilities offered by time-use surveys to measure contact patterns and to explain observed seroprevalence profiles. The authors first develop a methodology to estimate time-of-exposure matrices, and then they apply it to time-use data for the United States (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). Finally, the authors estimate age-specific transmission parameters for varicella, commonly known as ''chickenpox,'' from age-specific time-of-exposure and seroprevalence data (United States, 1988-1994. The estimated time-of-exposure matrix reveals a strong element of assortativeness by age. In addition, there are peaks of exposure between people who were born one generation apart (i.e., parents and their children). Models based on the estimated age-specific transmission parameters fit the observed patterns of infection of endemically circulating varicella in a satisfactory way. The availability of time-use data for a large number of countries and their potential to supplement contact surveys make the methods developed extremely valuable and suitable for implementation in several different contexts.

Abstract Little is known on how different levels of population heterogeneity and different patter... more Abstract Little is known on how different levels of population heterogeneity and different patterns of human mobility affect the course of pandemic influenza in terms of timing and impact. By employing a large-scale spatially explicit individual-based model, founded on a highly detailed model of the European populations and on a careful analysis of air and railway transportation data, we provide quantitative measures of the influence of such factors at the European scale.

Background The 2009 H1N1 pandemic influenza dynamics in Italy was characterized by a notable patt... more Background The 2009 H1N1 pandemic influenza dynamics in Italy was characterized by a notable pattern: as it emerged from the analysis of influenza-like illness data, after an initial period (September–mid-October 2009) characterized by a slow exponential increase in the weekly incidence, a sudden and sharp increase of the growth rate was observed by mid-October. The aim here is to understand whether spontaneous behavioral changes in the population could be responsible for such a pattern of epidemic spread.

Riassunto: Il rischio di una pandemia influenzalee diventato piu sostanziale e persistente alla f... more Riassunto: Il rischio di una pandemia influenzalee diventato piu sostanziale e persistente alla fine del 2003, quando sie osservata una rapida crescita della diffusione del virus A (H5N1). In questo lavoro proponiamo un modello stocastico ad agenti individuali per verificare l'efficacia di alcune strategie di contenimento, quali vaccinazione, profilassi antivirale, misure per l'aumento della distanza sociale e limitazione dei voli aerei internazionali.

Beyond control measures imposed by public authorities, human behavioral changes can be triggered ... more Beyond control measures imposed by public authorities, human behavioral changes can be triggered by uncoordinated responses driven by the risk perception of an emerging epidemic. In order to account for spontaneous social distancing, a model based on an evolutionary game theory framework is here proposed. Behavioral changes are modeled through an imitation process in which the convenience of different behaviors depends on the perceived prevalence of infections.

SUMMARY We describe the real-time modelling analysis conducted in Italy during the early phases o... more SUMMARY We describe the real-time modelling analysis conducted in Italy during the early phases of the 2009 A/H1N1v influenza pandemic in order to estimate the impact of the pandemic and of the related mitigation measures implemented. Results are presented along with a comparison with epidemiological surveillance data which subsequently became available.

To investigate the 1918/19 influenza pandemic daily number of new hospitalizations in the only ho... more To investigate the 1918/19 influenza pandemic daily number of new hospitalizations in the only hospital in Florence (Central Italy) were analyzed. In order to describe the transmission dynamics of the 1918/1919 pandemic influenza a compartmental epidemic model was used. Model simulations show a high level of agreement with the observed epidemic data.

Evidence of preferential mixing through selected social routes has been suggested for the transmi... more Evidence of preferential mixing through selected social routes has been suggested for the transmission of tuberculosis (TB) infection in low burden settings. A realistic modelization of these contact routes is needed to appropriately assess the impact of individually targeted control strategies, such as contact network investigation of index cases and treatment of latent TB infection (LTBI).

We developed a stochastic individual-based discrete-time model to assess the impact of pandemic i... more We developed a stochastic individual-based discrete-time model to assess the impact of pandemic influenza containing strategies. The spread of influenza was then modeled with specific levels for households, schools/workplaces, and random contacts. We considered different R0 values (1.4, 1.7, 2), evaluating the impact of combined preventive measures (vaccination, antiviral prophylaxis (AVP), border restrictions and increased social distancing).

Viral hepatitis A, as other endemic diseases, represents a public health priority worldwide. To s... more Viral hepatitis A, as other endemic diseases, represents a public health priority worldwide. To study long-time scale human pathogens through individual-based simulations, the development of a dynamic network of contacts is required. In this work, we introduce an individual-based model accounting for the birth and death of the individuals, the generation of new households, and the educational career of the individuals, in order to investigate viral hepatitis A dynamics in the most affected Italian areas.

Influenza pandemics in the last century were characterized by successive waves and differences in... more Influenza pandemics in the last century were characterized by successive waves and differences in impact and timing between different regions, for reasons not clearly understood. The 2009 H1N1 pandemic showed rapid global spread, but with substantial heterogeneity in timing within each hemisphere.

Little is known on how different levels of population heterogeneity and different patterns of hum... more Little is known on how different levels of population heterogeneity and different patterns of human mobility would affect the course of an epidemic in terms of timing and impact. By employing a large-scale spatially-explicit individual-based model, based on a highly detailed model of the European populations and on a carefully analysis of air and railway transportation data, we provide quantitative measures of their effects at European level.

Background Individual based models have become a valuable tool for modeling the spatiotemporal dy... more Background Individual based models have become a valuable tool for modeling the spatiotemporal dynamics of epidemics, eg influenza pandemic, and for evaluating the effectiveness of intervention strategies. While specific contacts among individuals into diverse environments (family, school/workplace) can be modeled in a standard way by employing available socio-demographic data, all the other (unstructured) contacts can be dealt with by adopting very different approaches.

Abstract Botnets have become the most sophisticated and dangerous way of spreading malware. Their... more Abstract Botnets have become the most sophisticated and dangerous way of spreading malware. Their damaging actions can range from massive dispatching of e-mail messages, to denial of service attacks, to collection of private and sensitive information. Unlike standard computer viruses or worms, botnets spread silently without actively operating their damaging activity, and then are activated in a coordinated way to maximize the``benefit''of the malware.

Marburg hemorrhagic fever is rare yet among the most severe diseases affecting humans, with case ... more Marburg hemorrhagic fever is rare yet among the most severe diseases affecting humans, with case fatality ratio even higher than 80%. By analyzing the largest documented Marburg hemorrhagic fever epidemic, which occurred in Angola in 2005 and caused 329 deaths, and data on viral load over time in non-human primates, we make an assessment of transmissibility and severity of the disease. We also give insight into the control of new Marburg hemorrhagic fever epidemics to inform appropriate health responses.

We study how spontaneous reduction in the number of contacts could develop, as a defensive respon... more We study how spontaneous reduction in the number of contacts could develop, as a defensive response, during an epidemic and affect the course of infection events. A model is proposed which couples an SIR model with selection of behaviours driven by imitation dynamics. Therefore, infection transmission and population behaviour become dynamical variables that influence each other. In particular, time scales of behavioural changes and epidemic transmission can be different.

Mathematical models are powerful tools for simulating plausible epidemic spread scenarios and for... more Mathematical models are powerful tools for simulating plausible epidemic spread scenarios and for evaluating the impact of control policies. They represent the scientific basis on which public health policy makers should take their decisions on the intervention strategies that should be performed at local, national and international scale. In this context, Individual-Based simulation Models (IBM) have become one of the much relevant approaches.

During summer 2007 Italy has experienced an epidemic caused by Chikungunya virus–the first large ... more During summer 2007 Italy has experienced an epidemic caused by Chikungunya virus–the first large outbreak documented in a temperate climate country–with approximately 161 laboratory confirmed cases concentrated in two bordering villages in North–Eastern Italy comprising 3,968 inhabitants. The seroprevalence was recently estimated to be 10.2%.