Title: Introduction of Epidemiology
1Introduction of Epidemiology
- SUNPETCH ANGKITITRAKUL, Ph.D.
- ??????? ?????????????
2One World One Health
- One World Earth
- One Health Humans, Animals, Environment
- Emerging Infectious Disease (EID)
- Avian Influenza (H5N1),
- SARS (Severe Acute Respiratory Syndrome)
- Nipah virus
- Influenza A (H1N1)
3Emerging 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
4Re-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
5Emerging and re-emerging Infectious Diseases
6Global of emerging and re-emerging infectious
diseases
7Factors of EID
- Humans (Africa, Asia and Latin America)
- Wildlife (Forest encroachment)
- Climate change
- Pathogens
- Spread of pathogen (air or insect)
- Virus (mutation)
8(No Transcript)
9Epidemiology
- Epi on, upon
- Demos people
- Logos knowledge
10Historical 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)
11What 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)
12What 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
13Epidemiology
is a scientific discipline
that involves the study of
the frequency
and distribution
of health and disease
in populations
in order to find risk factors
for prevention and control
14Discipline 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
15Health 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
16Risk 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
17Objective 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
18Objective 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
19Use of Epidemiology
- 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
20Epidemiology VS Clinical medicine
Epidemiology Clinical medicine
Population People (Case)
Prevention and control Treatment
Epidemiologist Case
Healthy in population Healthy in people
21Field 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
22Field 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
23Goal ofVeterinary field epidemiology
- Prevention and control disease agents
- Health of animals, humans and environment
- Concepts and methods of epidemiology
- Practical and information
24Epidemiology 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
25Endemic (????????????)
- 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
26Sporadic pattern
27Epidemic (????????)
- 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
28Epidemic pattern
29Epidemic patterns
30Disease outbreak
- survey of disease data
- count of cases
- describe
- person / animal
- place
- time
31Relax
32(No Transcript)
33(No Transcript)
34(No Transcript)
35Agents
- Biological
- Viruses Bacteria Parasites or prions
- Chemical
- Toxins
- Man-made (Dioxins and melamine)
- Inorganic/organic zearalenone
- Physical
- Foreign bodies
- Trauma
- Radiation
36Agent Factors
- Dose
- Environmental hardiness
- Virulence (microbial)
- Infectivity (microbial)
- Toxicity (poisons)
37Host
- Natural host
- agent has adapted itself and co-exists in balance
in the host - Atypical host
- agent is not normally encountered
38Host
- Demography
- Age, Sex, Species, Breed
- Production type / level, Density
- Biology
- Genetics, behavior
- Management
- Intensive (housing) / extensive (free roaming)
- Nutrition
- Hygiene
- Husbandry
- Vaccination / medication
39Host
- 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
40Host Factors
- Innate resistance (e.g. gastric barrier,
mucocilliary transport mechanism) - Previous exposure
- Passive immune status (neonates)
- Vaccination status and response
- Age
- Gender
41Host Factors
- Behavior (e.g. mutual grooming, dominance, pica)
- Production status (e.g., lactating vs.
non-lactating) - Reproductive status (e.g., pregnant vs.
non-pregnant, sterile vs. intact) - Genetics
42Environment
- Natural environment
- Geography
- Climate
- Season
- pH
- Ammonia concentration
- Water activity
- Ultraviolet light
- Organic matter
43- 2) Human aspects
- Animal management systems
- Marketing systems and economics
- Government policies
44Environmental Factors
- 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)
45Example
- 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."
46Break 15 mins
47Natural history of disease
48Natural history of disease
- Stage of susceptibility
- Stage of preclinical disease
- Stage of clinical disease
- Stage of disability
49Iceberg principle of disease
50Iceberg (phenomenon) Principle
51Iceberg phenomenon
52Steps in the Disease Process
53Concept of Causation
- The basis for most epidemiological investigations
- To identify causal relationships and potential
risk factors - A framework for identifying causes of infectious
disease
54Kochs 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.
55Causation 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
56Causation 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
57Sources of infectious disease
- Environment
- Live Animals / Dead animals
- Feed and Water
- Animal products
- Animal by-products
- Reservoir (wild animals, insects)
- Fomites (clothing, equipment, vehicles)
- Vectors (insects)
58Exposure
- 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
59(No Transcript)
60Host susceptibility
- Species, breed, strain
- Age
- Sex
- Genetics
- Animal management and husbandry
61Infectious 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
62Infectivity
- the percentage (or proportion) of individuals
exposed to a particular agent who become infected
Infectivity
63Pathogenicity
- the percentage of infected individuals who
develop clinical disease due to the particular
agent
Pathogenicity
64Virulence
- the percentage of individuals with clinical
disease who become serious ill or die
Virulence
65Mode of Transmission
- Direct Transmission
- Direct contact
- Droplet spread
- Indirect
- Air borne
- Vehicle borne (food water)
- Vector borne (arthropods ticks, mosquitoes)
66- Influenza droplet spread, vehicle borne
- Salmonella vehicle borne, direct contact
- TB air borne
- Cutaneous Anthrax direct contact
- Pneunonic Plague air borne
67Type 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
68(No Transcript)
69Descriptive epidemiology
Time
Distribution
Place
Descriptive study
Person
Epidemiology
Risk factors
Analytic study
Etiology
70Descriptive epidemiology
- What (How much) occurred
- Who animals or humans
- When time
- Where place
71Descriptive epidemiology
- 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
72Descriptive epidemiology
- Generate hypotheses and ideas for further
research - Evaluation of prevention and control measures
- Support planning activities for animal health
program
73Basic Measures and Tools of Descriptive
Epidemiology
- Data collection
- classification / organization
- summarizing
- presentation
74Incidence
- the number of NEW cases that develop over a
certain time period.
75Incidence rate
x100
76Prevalence
- the number of existing cases including old and
new cases that have developed at some point
during a time period.
77Prevalence rate
x100
78Incidence and Prevalence
79(No Transcript)
80Example
Question Type of measure
Do you currently have asthma? Point prevalence
Have you had asthma during the last 2 years? Period prevalence
Have you ever had asthma? Cumulative incidence
81(No Transcript)
82(No Transcript)
83(No Transcript)
84Analytical epidemiology
- How adjust policy and response
- Why prevent and control
85Cross-sectional
- A random sample of individuals from a population
is taken at a point in time - Surveys to collect data
86Cross-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
87Cohort
- 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
88Cohort
89Cohort
- Advantages
- monitored over time for disease occurrence
- estimates of the absolute incidence of disease in
exposed and non-exposed - Disadvantages
- long follow-up period
- case of rare diseases large groups are necessary
- Losses to follow-up
- expensive
90Case-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
91(No Transcript)
92Case-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
93(No Transcript)
94confuse
95Thank you