Ping Yan

Ping Yan
Public Health Agency of Canada | PHAC · Infectious Disease Prevention and Control Branch

PhD

About

52
Publications
12,820
Reads
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2,129
Citations
Introduction
Ping Yan currently works at the Infectious Disease Prevention and Control Branch, Public Health Agency of Canada. Ping applies biostatistics, applied probability and mathematical models in the area of epidemiology of communicable disease transmisson and control. He both manages a research group in disease modelling and publishes his own research in collaboration with other scientists.
Additional affiliations
September 2003 - present
May 1992 - September 2003
Education
September 1987 - September 1992
University of Waterloo
Field of study
  • Statistics
September 1986 - August 1987
University of Waterloo
Field of study
  • Statistics
March 1978 - July 1982

Publications

Publications (52)
Article
Two approximations are commonly used to describe the spread of an infectious disease at its early phase: (i) the branching processes based on the generation concept and (ii) the exponential growth over calendar time. The former is characterized by a mean parameter: the reproduction number R(0). The latter is characterized by a growth rate rho, also...
Article
We use distribution theory and ordering of non-negative random variables to study the Susceptible-Exposed-Infectious-Removed (SEIR) model with two control measures, quarantine and isolation, to reduce the spread of an infectious disease. We identify that the probability distributions of the latent period and the infectious period are primary featur...
Article
Use of the final size distribution of minor outbreaks for the estimation of the reproduction numbers of supercritical epidemic processes has yet to be considered. We used a branching process model to derive the final size distribution of minor outbreaks, assuming a reproduction number above unity, and applying the method to final size data for pneu...
Book
Full-text available
This book provides a systematic treatment of the mathematical underpinnings of work in the theory of outbreak dynamics and their control, covering balanced perspectives between theory and practice including new material on contemporary topics in the field of infectious disease modelling. Specifically, it presents a unified mathematical framework li...
Article
Full-text available
During an epidemic, accurate estimation of the numbers of viral infections in different regions and groups is important for understanding transmission and guiding public health actions. This depends on effective testing strategies that identify a high proportion of infections (that is, provide high ascertainment rates). For the novel coronavirus SA...
Article
Full-text available
During a pandemic, data are very “noisy” with enormous amounts of local variation in daily counts, compared with any rapid changes in trend. Accurately characterizing the trends and reliable predictions on future trajectories are important for planning and public situation awareness. We describe a semi-parametric statistical model that is used for...
Article
Full-text available
Background The COVID-19 pandemic has had an unprecedented impact on citizens and health care systems globally. Valid near-term projections of cases are required to inform the escalation, maintenance and de-escalation of public health measures, and for short-term health care resource planning. Methods Near-term case and epidemic growth rate project...
Article
Full-text available
The 2018–2020 Ebola outbreak in the Democratic Republic of the Congo is the first to occur in an armed conflict zone. The resulting impact on population movement, treatment centres and surveillance has created an unprecedented challenge for real-time epidemic forecasting. Most standard mathematical models cannot capture the observed incidence traje...
Preprint
Full-text available
The 2018-20 Ebola outbreak in the Democratic Republic of the Congo is the first to occur in an armed conflict zone. The resulting impact on population movement, treatment centers, and surveillance has created an unprecedented challenge for real-time epidemic forecasting. Most standard mathematical models cannot capture the observed incidence trajec...
Article
Full-text available
Background: As of March 31, 2020, the ongoing COVID-19 epidemic that started in China in December 2019 is now generating local transmission around the world. The geographic heterogeneity and associated intervention strategies highlight the need to monitor in real time the transmission potential of COVID-19. Singapore provides a unique case example...
Article
Full-text available
The ongoing COVID-19 epidemic continues to spread within and outside of China, despite several social distancing measures implemented by the Chinese government. Limited epidemiological data are available, and recent changes in case definition and reporting further complicate our understanding of the impact of the epidemic, particularly in the epide...
Article
Full-text available
The initial cluster of severe pneumonia cases that triggered the COVID-19 epidemic was identified in Wuhan, China in December 2019. While early cases of the disease were linked to a wet market, human-to-human transmission has driven the rapid spread of the virus throughout China. The Chinese government has implemented containment strategies of city...
Preprint
Full-text available
The initial cluster of severe pneumonia cases that triggered the 2019-nCoV epidemic was identified in Wuhan, China in December 2019. While early cases of the disease were linked to a wet market, human-to-human transmission has driven the rapid spread of the virus throughout China. The ongoing outbreak presents a challenge for modelers, as limited d...
Article
Full-text available
in the Democratic Republic of the Congo, has been exacerbated by deliberate attacks on healthcare workers despite vaccination efforts. Using a mathematical/statistical modelling framework, we present the quantified effective reproduction number (Rt) at national and regional levels as at 29 September. The weekly trend in Rt displays fluctuations whi...
Chapter
If the outcome is the former, what is the expected total number of infected individuals and what is the expected time to extinction?
Chapter
As we have emphasized in Chaps. 4 and 5, simple homogeneous models of transmission or growth dynamics often yield an early exponential epidemic growth phase even when the population is stratified into different groups (e.g., age, gender, regions). However, recent work has highlighted the presence of early sub-exponential growth patterns in case inc...
Chapter
Emerging and re-emerging infectious diseases pose major challenges to public health worldwide. Fortunately mathematical and statistical inference and simulation approaches are part of the toolkit for guiding prevention and response plans. As the recent 2013–2016 Ebola epidemic exemplified, an unfolding infectious disease outbreak often forces publi...
Chapter
We have seen that, under suitable assumptions such as homogeneous mixing, the basic reproduction number R0, defined at the start of the epidemic and given by ( 4.2) in Chap. 4, transcends to the asymptotic equilibrium (t →∞) outcomes such as the final size ( 5.32) in a closed population or the endemic equilibrium \(x(\infty )=\lim _{t\rightarrow \i...
Chapter
We now turn our attention to the population level dynamics and ask phenomenological questions. First, many important measures in the study of infectious diseases are count variables N, taking integer values n = 0, 1, 2, ….
Chapter
All the models presented in the previous chapters are parametric. They belong to different types and serve different purposes.
Chapter
We consider that at the beginning, t = 0, there is no disease. We call the system at this condition the disease-free equilibrium. We assume that the entire population is susceptible. The size of the susceptible population is denoted by m.
Chapter
We start with simple models that describe the dynamics of disease transmission over time t in a constant population of size m and investigate the long-term epidemic dynamics as t →∞. In these simple models, we assume there is no replacement of susceptible individuals due to demographic input of susceptible newborns. The population is partitioned in...
Article
Full-text available
Background While combination antiretroviral therapy (cART) has significantly improved survival times for persons diagnosed with HIV, estimation of life expectancy (LE) for this cohort remains a challenge, as mortality rates are a function of both time since diagnosis and age, and mortality rates for the oldest age groups may not be available. Meth...
Data
SAS macros, sample program and documentation. (ZIP)
Data
Excel workbook with supporting tables and data corresponding to figures. (XLSX)
Article
Full-text available
Motivated by the vision of the Joint United Nations Programme on HIV/AIDS that 90% of people living with HIV will be diagnosed by year 2020, we present an optimization framework regarding repeated testing of an infectious disease which is transmitted unevenly in the population. A subset of HIV surveillance data in Canada with detailed and compatibl...
Article
Full-text available
For an intervention against the spread of communicable diseases, the idealized situation is when individuals fully comply with the intervention and the exposure to the infectious agent is comparable across all individuals. Some level of non-compliance is likely where the intervention is widely implemented. The focus is on a more accurate view of it...
Article
Full-text available
Background: Prevalence estimates contribute to our understanding of the magnitude of a particular health condition and in planning appropriate public health interventions. Objective: To estimate the prevalence of chronic Hepatitis C virus (HCV) infection, anti-HCV-positive status (anti-HCV) and the proportion of undiagnosed HCV infections in Can...
Article
Full-text available
Background Hepatitis C virus (HCV) infection has a high likelihood of becoming chronic and lead to a range of conditions with poor health outcomes. Identifying birth groups highly affected by HCV infection may better focus public health interventions and ensure their cost-effectiveness. Our analysis focused on studying the association of the birth...
Article
We propose a new approach to estimate the number of new infections with the human immunodeficiency virus (HIV), by integrating the back-calculation method based on HIV diagnostic data with proportions of recent infections among newly diagnosed individuals. This is done by establishing an explicit link between the distribution of time-since-infectio...
Article
Full-text available
Many people who are HIV positive are unaware of their infection status. Estimation of the number of people with undiagnosed HIV within a country or region is vital for understanding future need for treatment and for motivating testing programs. We review the available estimation approaches which are in current use. They can be broadly classified in...
Article
Full-text available
We describe the application of mathematical models in the study of disease epidemics with particular focus on pandemic influenza. We outline the general mathematical approach and the complications arising from attempts to apply it for disease outbreak management in a real public health context.
Article
Full-text available
To estimate the number of prevalent and incident HIV infections in Canada in 2008. We applied multiple methods to estimate national HIV prevalence and incidence in Canada, including the workbook method, two statistical modelling methods, and an iterative spreadsheet model. The estimated number of people living with diagnosed or undiagnosed HIV infe...
Article
The aim of the study was to reconstruct the HIV epidemic in Australia for selected populations categorized by exposure route; namely, transmission among men who have sex with men (MSM), transmission among injecting drug users (IDUs), and transmission among heterosexual men and women in Australia. Statistical back-projection techniques were extended...
Article
The threat of 2009 pandemic influenza A (H1N1) is still causing widespread public concern. A comprehensive understanding of the epidemiology of 1918 pandemic influenza commonly referred to as the Spanish flu may be helpful in offering insight into control strategies for the new pandemic. We explore how the preparedness for a pandemic at the communi...
Article
Full-text available
In the face of an influenza pandemic, accurate estimates of epidemiologic parameters are required to help guide decision-making. We sought to estimate epidemiologic parameters for pandemic H1N1 influenza using data from initial reports of laboratory-confirmed cases. We obtained data on laboratory-confirmed cases of pandemic H1N1 influenza reported...
Article
Full-text available
We set out to estimate historical trends in HIV incidence in Australian men who have sex with men with respect to age at infection and birth cohort. A modified back-projection technique is applied to data from the HIV/AIDS Surveillance System in Australia, including "newly diagnosed HIV infections", "newly acquired HIV infections" and "AIDS diagnos...
Article
Given the enormity of challenges involved in pandemic preparedness, design and implementation of effective and cost-effective public health policies is a major task that requires an integrated approach through engagement of scientific, administrative, and political communities across disciplines. There is ample evidence to suggest that modeling may...
Article
Full-text available
The BED Capture Enzyme Immunoassay, believed to distinguish recent HIV infections, is being used to estimate HIV incidence, although an important property of the test--how specificity changes with time since infection--has not been not measured. We construct hypothetical scenarios for the performance of BED test, consistent with current knowledge,...
Chapter
Mathematical epidemiology differs from most sciences in a way that it does not lend itself to experimental validation of models. Models involve sequences of events. Each pair of successive events is composed of an initiating event that leads to a subsequent event. All these events are generated through some stochastic mechanisms. Data are observati...
Chapter
Full-text available
The occurrence of a major outbreak, the shape of the epidemic curves, as well as the final sizes of outbreaks, are realizations of some stochastic events with some probability distributions. These distributions are manifested through some stochastic mechanisms. This chapter divides a typical outbreak in a closed population into two phases, the init...
Article
Full-text available
Given the danger of an unprecedented spread of the highly pathogenic avian influenza strain H5N1 in humans, and great challenges to the development of an effective influenza vaccine, antiviral drugs will probably play a pivotal role in combating a novel pandemic strain. A critical limitation to the use of these drugs is the evolution of highly tran...
Article
Full-text available
The emergence of drug resistance in treated populations and the transmission of drug resistant strains to newly infected individuals are important public health concerns in the prevention and control of infectious diseases such as HIV and influenza. Mathematical modelling may help guide the design of treatment programs and also may help us better u...
Article
This article describes the methods, results and future perspectives of four information sources used to monitor the HIV epidemic in Canada: AIDS case surveillance, HIV case surveillance, HIV sentinel serosurveillance, and behavioral surveillance. Synthesizing data from these multiple sources provides a more comprehensive picture of the HIV epidemic...
Article
Multi-state Markov models can be useful in analysing disease history data. We apply the general estimation methods of Kalbfleisch and Lawless to panel data in which individuals are viewed over only a portion of their life history and complete information about transition times between states is unavailable. Methods to assess goodness-of-fit are pro...
Article
This article describes a sampling and estimation scheme for estimating the size of injecting drug use (IDU) population using Needle Exchange Programs (NEPs). It is designed to use the information of number of needles distributed in the NEPs centres. The approach involves a sampling design to collect a sample of injecting drug users (IDUs) who appea...

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Projects

Projects (3)
Archived project
Combining Operations Research with biostatistics, given the background context to fulfill the Joint United Nations Programme on HIV/AIDS (UNAIDS) vision that 90% of all people living with HIV will have been diagnosed by year 2020, the question is under what principles that one should select the optimal HIV testing strategy in a population composed of subpopulations with different levels of transmission rates.
Archived project
For an intervention against the spread of communicable diseases, when individuals fully comply with the intervention and the exposure to the infectious agent is comparable across all individuals, this is the idealized situation. Some level of non-compliance is likely where an intervention to be widely implemented. A frailty model is applied. The goal is to show that , under the influence of between-individual heterogeneity, the value of the controlled reproduction number along with its derived quantities with epidemiologic relevance, are invariant of time scale and robust to the underlying model assumptions.
Archived project
The goal of this project is to adapt the standard abridged life table approach for the calculation of Life Expectancy (LE) to disease-specific cohorts. For a disease specific cohort the mortality rate may be significantly elevated at the time of diagnosis and then become much lower during periods of remission. Also, for emerging diseases such as HIV or HCV, the disease prevalence among older 5-year age groups is insufficient for the calculation of mortality rates for these age groups. We plan to created a SAS macro to calculate LE using the Chiang II algorithm. The Chiang II algorithm is recommended for small populations where some age groups may contain zero deaths. We will add a module to include mortality rates stratified by time since diagnosis and a module to project excess mortality based on mortality rates from the reference population.