Transcript Intro to Epidem-

Introduction of Epidemiology
SUNPETCH ANGKITITRAKUL, Ph.D.
สรรเพชญ อังกิติตระกูล
One World One Health
• One World: Earth
• One Health: Humans, Animals, Environment
• Emerging Infectious Disease (EID)
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Avian Influenza (H5N1),
SARS (Severe Acute Respiratory Syndrome)
Nipah virus
Influenza A (H1N1)
Emerging Infectious Diseases
• infectious diseases with an increasing in
patient report over the past 20 years
• infectious diseases with an increasing
possibility in the near future
• AIDS, Avian Influenza, and drug resistant
tuberculosis
• Antimicrobial resistant organisms
Re-emerging Infectious Diseases
• infectious diseases that used to create
outbreak in the past and subsided for a
number of years but are occurred again
• tuberculosis, hemorrhage fever and malaria
Emerging and re-emerging
Infectious Diseases
Global of emerging and re-emerging infectious diseases
Factors of EID
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Humans (Africa, Asia and Latin America)
Wildlife (Forest encroachment)
Climate change
Pathogens
– Spread of pathogen (air or insect)
– Virus (mutation)
Epidemiology
• Epi = on, upon
• Demos = people
• Logos = knowledge
Historical of epidemiology
• Hippocrates (400 BC)
• John Graunt (1662)
• John Snow (1854)
– Out break of cholera occurred in a small area of
central London (Golden Square)
What is Epidemiology?
• The study of the distribution and
determinants of health-related states or
events in specified populations and the
application of this study to the control of
health problems (CDC)
What is Epidemiology?
• focused on the health and disease status
of a population
• the study of how disease is distributed in
populations and the factors that influence
or determine this distribution
Epidemiology
is a scientific discipline
that involves the study of
the frequency
and distribution
of health and disease
in order to find risk factors
in populations
for prevention and control
Discipline: the general approach is to creating order and
structure from incomplete knowledge
Study: combines learning about epidemiology theory with
on the job field application
Frequency: means that we count characteristics in a
population of people or animals
Distribution: describes the patterns of disease in a
population, in a particular place during a period of time
Health: refers to measures of optimum productivity
due to lack of disease (meat, eggs or milk)
Disease: refers generally to an imbalance in the health
status of individuals or populations that result in
decreased productivity, illness or death
Population: refers to the group of individual animals or
people that are considered or affected
Risk factors: risk is the probability that a factor the
population is exposed to be associated with the
occurrence of disease
Prevent: means not providing the opportunity for a
disease to occur
Control: method to reduce the extent of disease in a
population or area
Objective of Epidemiology
• To identity the etiology (cause) of disease
and the relevant risk factors
• To determine the extent of disease found in
the community
• To study the natural history and prognosis
of disease
Objective of Epidemiology
• To evaluate both existing and newly
developed preventive and therapeutic
measure and modes of health care
delivery
• To provide the foundation for developing
public policy relating to environmental
problems
Use of Epidemiology
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Describe the distribution of disease
Describe the natural history of disease
Identify factors that increase/decrease risk
Predict trends
Consider mechanisms of transmissions
Test efficacy & evaluate interventions
Identify health needs
Epidemiology VS Clinical medicine
Epidemiology
Clinical medicine
Population
People (Case)
Prevention and control
Treatment
Epidemiologist
Case
Healthy in population
Healthy in people
Field Epidemiology
• Field Epidemiology is the front line
• There is health emergency or an immediate
need to understand the health status of a
population
• Emerging Infectious Disease (EID): no
information, very limited
Field Epidemiology
• Attempts to gather and organize data to
bring order and meaning to it
• Can be applied to disease outbreaks,
situation assessments and policy
evaluation.
• Relies on a systematic approach to gather
and organize data in a way that will support
a better understanding of a disease situation
Goal of
Veterinary field epidemiology
• Prevention and control disease agents
• Health of animals, humans and environment
– Concepts and methods of epidemiology
– Practical and information
Epidemiology approach
• Try and understand what factors may be
increasing or reducing the risk of disease
• Promoting and protecting the health of
animal and human populations
Endemic (โรคประจำถิน่ )
• the constant occurrence of a disease that
commonly presents in a particular place with
stability in the level of infection
– Sporadic: An irregular occurrence of a disease
that commonly presents in a particular place
Endemic pattern
Sporadic pattern
Epidemic (โรคระบำด)
• the occurrence of a disease that the level of
infection exceeds that normal expectancy in
a specific region, spreads rapidly and
usually lasts for a limited period of time
– Pandemic: widespread epidemic that affects a
large part of population in many countries
– Epizootic: epidemic that involves animal host
population
Epidemic pattern
Epidemic patterns
Disease outbreak
• survey of disease data
• count of cases
• describe
– person / animal
– place
– time
Relax
Epidemiology triad: explain why diseases occur in a population
Host
Agent
Environment
Agent
Host
Host
Agent
Environment
Environment
Host
Environment
Host
Agent
Environment
Agent
Agents
• Biological
– Viruses Bacteria Parasites or prions
• Chemical
– Toxins
– Man-made (Dioxins and melamine)
– Inorganic/organic: zearalenone
• Physical
– Foreign bodies
– Trauma
– Radiation
Agent Factors
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Dose
Environmental hardiness
Virulence (microbial)
Infectivity (microbial)
Toxicity (poisons)
Host
• Natural host:
– agent has adapted itself and co-exists in
balance in the host
• Atypical host:
– agent is not normally encountered
Host
• Demography
– Age, Sex, Species, Breed
– Production type / level, Density
• Biology
– Genetics, behavior
• Management
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Intensive (housing) / extensive (free roaming)
Nutrition
Hygiene
Husbandry
Vaccination / medication
Host
• Marketing
– Profitability related to prices (economics)
– Distance from market
• Herd immunity
– Innate (genetic capability)
– Acquired through vaccination or deliberate
exposure
– Proportion of total population that is resistant to
a disease agent
• Susceptibility
– Lack of resistance to the disease agent
Host Factors
• Innate resistance (e.g. gastric barrier,
mucocilliary transport mechanism)
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Previous exposure
Passive immune status (neonates)
Vaccination status and response
Age
Gender
Host Factors
• Behavior (e.g. mutual grooming, dominance, pica)
• Production status (e.g., lactating vs. nonlactating)
• Reproductive status (e.g., pregnant vs. nonpregnant, sterile vs. intact)
• Genetics
Environment
Natural environment
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Geography
Climate
Season
pH
Ammonia concentration
Water activity
Ultraviolet light
Organic matter
2) Human aspects
– Animal management systems
– Marketing systems and
economics
– Government policies
Environmental Factors
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Animal stocking density
Animal movement between groups
Housing (e.g. ventilation, sanitation)
Environmental conditions (e.g. temperature,
humidity, wind velocity, precipitation)
• Nutrition (protein, energy and macromineral and
micromineral adequacy)
Example
• Increased animal density may lead to increased
microbial load in the environment
•a roof may prevent exposure of microbe to killing UV
• low ventilation
• increase humidity
• increases environmental survival of the organism
• increases exposure dose and infects more animals.
"Bovine mastitis is a disease of man with signs in the cow."
"Bad management will overwhelm the best immunology."
Break 15 mins
Natural history of disease
Risk factors
Death
Normal
Disease
recover
disabled
Natural history of disease
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Stage of susceptibility
Stage of preclinical disease
Stage of clinical disease
Stage of disability
Iceberg principle of disease
Iceberg (phenomenon) Principle
Iceberg phenomenon
death
disability
Clinical
Clinical
Pre-clinical
Susceptibility
Healthy
Steps in the Disease Process
Agent source
Exposure
Host
susceptibility
Outcome
•Clinical
•Sub-clinical
Concept of Causation
• The basis for most epidemiological
investigations
• To identify causal relationships and potential
risk factors
• A framework for identifying causes of
infectious disease
Koch’s Postulates
• The agent has to be present in every case of
the disease.
• The agent has to be isolated and grown in
pure culture.
• The agent has to cause disease when
inoculated into a susceptible animal and the
agent must then be able to be recovered
from that animal and identified.
Causation of disease
• The agent
– Is present when the disease exists
– Is absent when the disease does not exist
– The agent can be isolated in pure culture and
results in disease when it is given to exposed
animals
• Exposure
– Occurs before the disease occurs
Causation of disease
• Consistency
– The disease is reproducible in different
populations at different times
• Strength of statistical association
– The results are not due to chance
• Dose-response
– Increase in exposure leads to increase in disease
Sources of infectious disease
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Environment
Live Animals / Dead animals
Feed and Water
Animal products
Animal by-products
Reservoir (wild animals, insects)
Fomites (clothing, equipment, vehicles)
Vectors (insects)
Exposure
• Initial introduction into the population
• Transmission within the population
• Direct transmission
• Horizontal
• Vertical
• Indirect transmission
• Marketing systems
• Exposure dose of disease agent
• Route of exposure
• Animal density
Host susceptibility
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Species, breed, strain
Age
Sex
Genetics
Animal management and husbandry
Infectious disease
• Three terms are used to describe an
infectious disease according to the various
outcomes that many occur after exposure to
the causative agent and their population
based definitions are given below
– Infectivity
– Pathogenicity
– Virulence
Infectivity
• the percentage (or proportion) of individuals
exposed to a particular agent who become
infected
Infectivity =
No of infected following exposure
Total of population at exposure
Pathogenicity
• the percentage of infected individuals who
develop clinical disease due to the particular
agent
Pathogenicity =
No of clinically affected following exposure
Total of infected at exposure
Virulence
• the percentage of individuals with clinical
disease who become serious ill or die
Virulence =
No of severe (fatal) cases following exposure
Total of clinically infected cases at exposure
Mode of Transmission
• Direct Transmission
– Direct contact
– Droplet spread
• Indirect
– Air borne
– Vehicle borne (food water)
– Vector borne (arthropods: ticks, mosquitoes)
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Influenza: droplet spread, vehicle borne
Salmonella: vehicle borne, direct contact
TB: air borne
Cutaneous Anthrax: direct contact
Pneunonic Plague: air borne
Type of Epidemiology
(Study design)
• Descriptive epidemiology
– survey: time, place, person
– Case report, case series
• Analytical epidemiology (risk factors)
– Cross-sectional
– Cohort
– Case-control
• Experimental epidemiology
– Randomized control trial
– Clinical trial
– Community trial
Epidemiology study
Distribution
Risk factors
Descriptive study
Analytic study
Descriptive epidemiology
Time
Descriptive study
Distribution
Place
Person
Epidemiology
Analytic study
Risk factors
Etiology
Descriptive epidemiology
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What (How much): occurred
Who: animals or humans
When: time
Where: place
Descriptive epidemiology
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Detection of individual case
Detection of outbreaks
Measuring the impact of disease
Understand the nature of a disease
Understand the way that disease spreads
and is distributed
Descriptive epidemiology
• Generate hypotheses and ideas for further
research
• Evaluation of prevention and control
measures
• Support planning activities for animal health
program
Basic Measures and Tools of
Descriptive Epidemiology
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Data collection
classification / organization
summarizing
presentation
Incidence
• the number of NEW cases that develop
over a certain time period.
Incidence rate
No. of new cases of a disease occurring in the population
during a specified period of time
No. of persons who are at risk of developing the disease
during that period of time
x100
Prevalence
• the number of existing cases including old
and new cases that have developed at some
point during a time period.
Prevalence rate
No. of cases of a disease present in the population
at a specified time
No. of persons in the population at that specified time
x100
Incidence and Prevalence
Example
Question
Do you currently have asthma?
Type of measure
Point prevalence
Have you had asthma during the last 2 years? Period prevalence
Have you ever had asthma?
Cumulative incidence
Morbidity rate =
Infection rate =
No of clinically ill
Population
No of infected
Population
Mortality rate =
Case fatality rate =
No of deaths
Population
No of deaths
No of clinically ill
Analytical epidemiology
• How: adjust policy and response
• Why: prevent and control
Cross-sectional
• A random sample of individuals from a
population is taken at a point in time
• Surveys to collect data
Cross-sectional
• Advantages:
– quick to conduct and cost is moderate compared
with other study designs.
• Disadvantages:
– cannot provide information on the incidence of
disease in a population only an estimate of
prevalence
– Difficult to investigate cause and effect
relationships
Cohort
• Comparing disease incidence over time
between groups
• Prospective cohort
– Non-disease case
– Expose and non-expose
• Retrospective cohort
– Disease case
– Evaluated for evidence of exposure to the agent
Cohort
Cohort
• Advantages:
– monitored over time for disease occurrence
– estimates of the absolute incidence of disease in
exposed and non-exposed
• Disadvantages:
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long follow-up period
case of rare diseases large groups are necessary
Losses to follow-up
expensive
Case-control
• Comparing the frequency of past exposure
between cases who develop the disease (or
other outcome of interest) and controls
chosen to reflect the frequency of exposure
in the underlying population at risk
Case-control
• Advantages:
– an efficient method for studying rare diseases
– subjects have experienced the outcome of
interest at the start of the study
– quick to run and cheaper than other study
• Disadvantages:
– Can not provide information on the disease
incidence in a population
– Reliant on the quality of past records or
recollection of study participants
– Difficult to ensure an unbiased selection of the
control group
confuse
Thank you