Applications of Public Health
knowledge
• As well as seeking to improve population health through the
implementation of specific population-level interventions, public
health contributes to medical care by identifying and assessing
population needs for health care services, including
• Assessing current services and evaluating whether they are
meeting the objectives of the healthcare system
• Ascertaining requirements as expressed by health professionals,
the public and other stakeholders
• Identifying the most appropriate interventions
• Considering the effect on resources for proposed interventions and
assessing their cost-effectiveness
• Supporting decision making in health care and planning health
services including any necessary changes.
• Informing, educating, and empowering people about health
issues
Nutritional epidemiology
farooq@asab.nust.edu.pk
Epidemiology
• Originally, the
study of epidemics
/ outbreaks
• Study of the factors
that contribute to
illness in
individuals and
communities, and
how to improve
health by altering
those factors
Epidemiology
and
Public Health
DEFINITIONS
• What is epidemiology?
• What is an epidemiologist?
How we view the world…..
• Pessimist: The
glass is half empty.
• Optimist: The glass
is half full.
• Epidemiologist: As
compared to what?
What is epidemiology?
EPIDEMIOLOGY is the study of
the nature, cause, control and
determinants of the frequency
and distribution of disease,
disability, and death in human
populations.
Epidemiology: the study of factors influencing the
occurrence, transmission, distribution, prevention and
control of disease in a defined population
What is epidemiology?
• “The study of skin diseases?”
• “The study of epidemics?”
• “The study of the distribution and
determinants of health-related states in
specified populations, and the
application of this study to control
health problems."
What is epidemiology?
EPIDEMIOLOGY is the study of the nature, cause, control
and determinants of the frequency and distribution of
disease, disability, and death in human populations.
 epidemiologists study sick and healthy people
 to determine the crucial difference between those who get the
disease and those who are spared
 epidemiologists study exposed and non-exposed people
 to determine the crucial effect of the exposure
An EPIDEMIOLOGIST is a public health
scientist, who is responsible for
carrying out all useful and effective
activities needed for successful
epidemiology practice
Disease-detective
Uses of Epidemiology..
Uses of Epidemiology..
Terminology
•
•
•
•
•
•
•
•
Endemic
Hyperendemic
Holoendemic
Epidemic/outbreak
Pandemic
Epizootic
Incidence
Prevalence
Terms used for reference
to various forms of
outbreaks
Endemic: a disease or pathogen present or usually prevalent in a given
population or geographic region at all times
Hyperendemic: equally endemic in all age groups of a population
Holoendemic: endemic in most of the children in a population, with the adults in the same population
being less often affected
Epidemic: a disease occuring suddenly in numbers far exceeding those
attributable to endemic disease; occurring suddenly in numbers clearly in excess
of normal expectancy
Pandemic: a widespread epidemic distributed or occurring widely throughout a
region, country, continent, or globally
Epizootic: of, or related to a rapidly spreading and widely diffused disease affecting large numbers of
animals in a given region
Incidence: rate of occurrence of an event; number of new cases of disease
occurring over a specified period of time; may be expressed per a known
population size
Prevalence: number of cases of disease occurring within a population at any one
given point in time
What is an Outbreak?
•
•
•
An outbreak is the occurrence
of more cases of a disease
than expected in a population
during a certain time
One case of smallpox,
anthrax, plague, botulism, or
tuberculosis anywhere in the
US is an outbreak requiring
immediate response
An epidemic and an outbreak
mean the same thing
– Epidemic is often applied
to an outbreak of special
concern
How Are Outbreaks Detected?
• Recognized and reported by
individual doctors or groups
(e.g., an emergency dept)
• Recognized and reported by
those affected (e.g.,
coworkers, school, banquet)
• Detected by PH agency
through review of individual
cases reported by doctors, or
review of lab reports or other
health care data
• Enhanced surveillance in
cooperation with state and
federal public health officials
Methods of Epidemiology
•
•
•
•
Public Health Surveillance
Disease Investigation
Analytic Studies
Program Evaluation
Surveillance
• The ongoing, systematic collection,
analysis, and interpretation of
health data essential to the
planning, implementation, and
evaluation of public health practice,
closely integrated with the timely
feedback of these data to those
who need to know.
In public health, ‘surveillance’
means tracking the occurrence of
diseases of importance – not
watching individuals or premises
Analytical studies
Observational:
Case-Control: Exposures, genes, and/or behaviors in
individuals with a particular disease (cases) are compared
to individuals without the disease (controls).
Cohort: A group of individuals with and without a particular
exposure are followed to compare disease outcomes.
Interventional:
Clinical Trials: Individuals are randomized to receive a
particular treatment within the clinic setting.
Community Trials: A community participates in a behavioral
intervention, a screening intervention, etc.
Analytical studies
Study Design:
Population-Based: Individuals under study
belong to a defined population, i.e., residents of
a geographic region.
Clinic or Hospital-Based: Studies are based
upon patients seen at a particular hospital or
clinic.
Community-Based: Participants are volunteers
in the community.
Analytical studies
Behavior, Genetics, Environment, Social/Cultural Risk Factors
Precancer
Risk Assessment,
Primary Prevention
Health
Cancer
Recurrence
Early Detection,
Secondary Prevention
•Etiologic studies
•Screening
•Genetic
•Chemoprevention
•Molecular
Trials
•Environmental
•Social/Cultural
•Behavioral Interventions
Survivorship
Tertiary Prevention
•Quality of life
•Predictors of survival
•Chemoprevention
Trials
All studies conducted in a population that is racially
and ethnically diverse
Population-Based Cancer Epidemiology
Surveillance Epidemiology and End Results
(SEER) Program
• Assemble and report estimates of cancer incidence and mortality in
the United States.
• Monitor annual cancer incidence trends.
• Provide continuing information on changes over time
in extent of disease at diagnosis, trends in therapy, and associated
changes in patient survival.
• Promote studies designed to identify factors amenable to cancer
control interventions.
Cancer In Arab Americans: Estimating Rates & Fostering
Research
Schwartz K, N01 PC35154-RRSS
•Arab–American women have similar distribution of
breast cancer histology to European–American
women.
•Arab–American stage, age, and hormone receptor
status at diagnosis was more similar to African–
American women.
•Arab–American women have a better overall
survival than even European–American women.
•Arab/Chaldean men had greater proportions of
leukemia , multiple myeloma, liver, kidney, and
urinary bladder cancers.
•Arab/Chaldean women had
greater proportions of leukemia, thyroid, and
brain cancers.
Jemal et. al., 2010
Trends in lung cancer mortality rates by sex in select countries, 1950-2006
Jemal et. al., 2010
Kinds of Epidemiology
• Descriptive
Study of the occurrence and
distribution of disease
• Analytic
Further studies to determine the
validity of a hypothesis
concerning the occurrence of
disease.
Deliberate manipulation of the
cause is predictably followed
by an alteration in the effect
not due to chance
• Experimental
Overview of epidemiologic design
strategies
• Descriptive
 Populations{Correlational studies}
 Individual
 Case report
 Case series
 Cross sectional studies
• Analytic studies
Observational
 Case control
 Cohort
 Retrospective
 Prospective
Interventional/Experimental
 Randomized controlled trial
 Field trial
 Clinical trial
Descriptive vs. Analytic Epidemiology
Descriptive
• Used when little is
known about the
disease
Analytic

Used when insight about
various aspects of disease
is available
• Rely on preexisting
data

Rely on development of
new data
• Who, where, when

Why
• Illustrates potential
associations

Evaluates the causality of
associations
Both are important!
Descriptive Studies
• Relatively inexpensive and less timeconsuming than analytic studies, they
describe,
• Patterns of disease occurrence, in terms of,
– Who gets sick and/or who does not
– Where rates are highest and lowest
– Temporal patterns of disease
• Data provided are useful for,
– Public health administrators (for allocation of resources)
– Epidemiologists (first step in risk factor determination)
Descriptive Epidemiology
• Correlational studies
• Case reports
• Case series
• Cross sectional studies
Correlational Studies (Ecological Studies)
• Uses measures that represent characteristics of
entire populations
• It describes outcomes in relation to age, time,
utilization of services, or exposures
• ADVANTAGES
– We can generate hypotheses for case-control studies
and environmental studies
– We can target high-risk populations, time-periods, or
geographic regions for future studies
Correlational Studies
• LIMITATIONS
– Because data are for groups, we cannot link disease and exposure
in individual
– We cannot control for potential confounders
– Data represent average exposures rather than individual exposures,
so we cannot determine a dose-response relationship
– Caution must be taken to avoid drawing inappropriate conclusions,
or ecological fallacy
Case Reports (case series)
• Report of a single individual or a group of
individuals with the same diagnosis
• Advantages
We can aggregate cases from disparate sources to generate
hypotheses and describe new syndromes
Example: hepatitis, AIDS
• Limitations
We cannot test for statistical association because there is no
relevant comparison group
Based on individual exposure {may simply be coincidental}
Case report/Case series(contd.)
• Important interface between clinical medicine &
epidemiology
• Most common type of studies published in
medical journals{1/3rd of all}
– AIDS ~ b/w oct1980-may81, 5 cases of P.carinii
pneumonia were diagnosed among previously healthy
young homosexual males in L.A.
Cross-Sectional Studies (prevalence studies)
• Measures disease and exposure simultaneously in a
well-defined population
• Advantages
– They cut across the general population, not simply those
seeking medical care
– Good for identifying prevalence of common outcomes, such as
arthritis, blood pressure or allergies
• Limitations
– Cannot determine whether exposure preceded disease
– It considers prevalent rather than incident cases, results will
be influenced by survival factors
– Remember: P = I x D
Cross-Sectional Studies
 Can be used as a type of analytic study for
testing hypothesis, when;
Current values of exposure variables are unalterable
over time
Represents value present at initiation of disease
E.g. eye colour or blood group
If risk factor is subject to alterations by disease, only
hypothesis formulation can be done
The epidemiologic approach:
Steps to public health action
DESCRIPTIVE
–
–
–
–
–
What (case
definition)
Who
(person)
Where
(place)
When (time)
How many
(measures)
ANALYTIC
–
–
Why
(Causes)
How
(Causes)
MEASURES
 Counts
 Times
 Rates
 Risks/Odds
 Prevalence
METHODS
 Design
 Conduct
 Analysis

Interpretation
ALTERNATIVE
EXPLANATIONS
 Chance
 Bias
 Confounding
ACTION
 Behavioural
 Clinical
 Community

Environmental
INFERENCES
 Epidemiologic
 Causal
Descriptive Epidemiology
• Study of the occurrence and distribution of
disease
• Terms:

Time

Place

Person
What are the three categories of
descriptive epidemiologic clues?
– □ Person: Who is getting sick?
– □ Place: Where is the sickness occurring?
– □ Time: When is the sickness occurring?
• PPT = person, place, time
Time
Secular



Periodic
Seasonal
Epidemic
Secular Trend
The long-time trend of disease
occurrence
Tetanus – by year, USA, 1955-2000
During 2000, a total of 35 cases of tetanus were reported. The percentage of cases among persons
aged 25-59 years has increased in the last decade. Note: A tetanus vaccine was first available in 1933.
900
800
700
600
500
400
300
200
100
0
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
Possible Reasons for Changes in
Trends
• Artifactual
–Errors in numerator due to
•Changes in the recognition of disease
•Changes in the rules and procedures for
classification of causes of death
•Changes in the classification code of causes of
death
•Changes in accuracy of reporting age at death
•Errors in the denominator due to error in the
enumeration of the population
Possible Reasons for Changes in
Trends (cont.)
• Real
– Changes in age distribution of the
population
– Changes in survivorship
– Changes in incidence of disease resulting
from
• Genetic factors
• Environmental factors
Other phrases
Cyclic trends ~ recurrent alterations in
occurrence , interval or frequency of
disease
Secular cyclicity
Levels of immunizations
Build up of susceptibles
e.g. Hep A-7 yr cycle,Measles-2yr cycle
Short term cyclicity
Chickenpox,salmonella(yearly basis)
Periodic Trend
Temporal interruption of the
general trend of secular variation
Whooping Cough - Four-monthly
admissions, 1954-1973
Seasonal
• A cyclic variation in disease
frequency by time of year & season.
Seasonal fluctuations in,
Environmental factors
Occupational activities
Recreational activities
Seasonal affective disorder
Seasonal Trend
Pneumonia-Influenza Deaths – By
year, 1934-1980
Person
Age
Sex
Occupation
Immunization status
Underlying disease
Medication
Nutritional status
Socioeconomic factors
Crowding
Hobbies
Pets
Travel
Personal Habits
Stress
Family unit
School
Genetics
Religion
Host.....
 Personal traits
 Behaviours
 Genetic predisposition
 Immunologic factor
Agent.....
Influence the chance
for disease or its Environment.....
severity
Contribute to the disease
Biological
process
 Physical
External conditions
 Chemical
Physical/biological/social
Epidemics Occur when.......
 host, agent and environmental factors are not
in balance
 due to new agent.
 due to change in existing agent (infectivity,
pathogenicity, virulence).
 due to change in number of susceptibles in the
population
 due
to
environmental
changes
that
affect
transmission
of the agent or growth of the agent.
INTRODUCTION to NE
To understand the relationship between diet and
long term health and disease
Incomplete understanding of biologic mechanisms
Inability to predict consequences of a food or nutrient.
Thus, the epidemiologic studies directly relating
intake of dietary components to risk of death or
disease
among
humans
play
a
critical
complementary role to laboratory investigation.
What is Nutritional epidemiology?
– Concept: diet influences occurrence of diseases
– Relatively new: the basic method used for > 200
years to identify essential nutrients
Nutritional epidemiology is a relatively new
discipline which combines the knowledge
compiled by nutritionists during this century
with
the
methodology
developed
by
epidemiologists to study the determinants of
diseases with multiple etiologies and long
latent periods.
【Example】 Observations that fresh fruits and
vegetables could cure scurvy by Lind in 1753.
Nutritional epidemiology
• Epidemiology is the study of the
occurrence of human diseases.
Nutritional epidemiology focuses on
the relationship between our diet and
our health.
History
• Scurvy
– Lind 1753
• Beriberi
– Kanehiro Takaki in 1884
• Rickets, pellagra
– Casimir Funk 1912
• Niacin (vit B3 deficiency)
– Dr.Joseph Goldberger 1915
– Conrad Elvehjem 1938
History
• Itai-itai disease "ouch ouch sickness”, was the
documented case of mass cadmium poisoning in
Toyama Prefecture, Japan. The cadmium poisoning
kidney failure. The disease is named for caused
softening of the bones and the severe pains
(Japanese: 痛い itai) caused in the joints and spine.
The term itai-itai disease was coined by locals.
• The cadmium was released into rivers by mining
companies in the mountains. The mining companies
were successfully sued for the damage.
Goals of nutritional epidemiology
• Monitoring the food consumption, nutrient intake
and nutritional status of a population.
• Generate new hypotheses about diet and
disease, to produce evidence that supports or
refutes existing hypotheses and to assess the
strength of diet-disease associations.
• Contribute to the prevention of disease and
improvement of public health
Goals of nutritional epidemiology
• Understanding the complex relationships between
diet and the major diseases (as cancer and
atherosclerosis)
• Having an overview of research strategies in
nutritional epidemiology
• Identifying methods of dietary assessment using
data on food intake, biochemical indicators of diet,
and measures of body size and composition.
• Discussing the analysis, presentation, and
interpretation of data from epidemiologic studies of
diet
Advantages of Nutritional Epidemiology
• Direct relevance to human health.
• The epidemiological results are used to calculate
direct estimates of risk, which can then be
translated into specific recommendations for
changes in nutrient intakes or food consumption
patterns.
• Findings from nutritional epidemiology can even
have direct implications for food processing and
technology
Example
High intakes of trans fatty acids (found in
margarine and other processed vegetable fats)
with increased risks of coronary heart disease
Difficulties
The most important one is the potential for
many kinds of bias.
Bias is defined as systematic error,
resulting in over- or underestimation of the
strength of an association between an
exposure and an outcome.
Studies in nutritional epidemiology must be
designed and executed with great care to
minimize bias.
The difficulty in determining whether observed
associations are causal. If the association
between a factor and a disease is not
causal, efforts to modify exposure to that
factor will not reduce disease risk.
Alcohol & lung cancer
The apparent simplicity and “real life” relevance of
epidemiological findings
encourage misuse & over-interpretation of data
when preliminary or unconfirmed findings come
to the attention of the news media and the
general public.
For example, the reports of an association between
margarine intake and cardiovascular disease may
have prompted some consumers to switch back to
butter, even though most experts believe that this
course of action would not be beneficial to
cardiovascular health.
Nutrition problems in the past
Typical deficiency syndromes
– Protein energy malnutrition
– Iron deficiency anemia
– Goiter
– High frequency among those with very low
intake
– Short latent periods
– Can be reversed within days or weeks
Contemporary nutritional epidemiology
Major diseases throughout the world
•
•
•
•
•
•
•
Heart disease
Cancer
Osteoporosis
Cataracts
Stroke
Diabetes
Congenital malformations
Why is it hard to study contemporary
nutrition-related disease?
Characteristics
1. Multiple determinants (causes)
diet, genetic, occupational, psychosocial, and
infectious factors; levels of physical activity;
behavioral characteristics
2. Long latent periods
cumulative exposure over many years, or
relatively short exposure occurring many years
before diagnosis
3. Occur with relatively low frequency
despite a substantial cumulative lifetime risk
4. Conditions not readily reversible
5. May result from excessive and/or insufficient
intake of dietary factors
Coronary heart disease
The complex nature of diet has posed an
unusually difficult challenge to nutritional
epidemiology:
– Diet represents an unusually complex set of
exposures that are strongly intercorrelated,
cannot be characterized as present or
absent
– Continuous variables often with a rather
limited range of variation
complex nature of diet
– Evolving patterns
– Preparatory methods
– Unawareness of nutrients
– Estimates
Comparison with another factor
"Do you eat?”
Vs.
“Do you smoke?”
Limitation in nutritional epidemiology
research:
-Lack of practical methods to measure diet for
large number of subjects
-Dietary assessment methods must be:
– Reasonably accurate
– Relatively inexpensive
-Diets of persons within one country are too
homogeneous to detect relationships with
disease.
Epidemiologic Approaches
to Diet and Disease
• Sources of the concepts, hypotheses, and techniques of
nutritional epidemiology:
-Biochemistry
-Cell culture methods
-Experiments in laboratory animals
-Metabolic and biochemical studies among human subjects
• Findings from in vitro studies and animal experiments
cannot be extrapolated directly to humans
• The basic science areas provide critical direction for
information that can aid in the interpretation of the
epidemiologic findings:
New methods for measuring genetic and environmental
exposures that can be applied in epidemiologic studies
Who is an epidemiologist?
• Many disciplines:
– Doctors (MD, DO, DVM, PhD)
– Nurses (RN, PHN)
– Laboratory workers (microbiologists,
technologists)
– Social workers, health educators
– Environmental health workers
– Attorneys
– Administrators
• Many have additional degrees/training
in public health
Goal of Epidemiologic Investigation:
Prevention
• This is the source of urgency
for PH staff
• Find and fix ongoing point
source (like contaminated
water supply)
• Close location until fixed
• Take food product off the
market
• Find, isolate, and treat
infectious people
• Find exposed people, give
them prophylactic treatment
or vaccine, and/or quarantine
them
Steps in an Outbreak
Investigation
• Detect problem by public
health surveillance
• Verify diagnosis
• Confirm outbreak
• Identify / count cases
• Characterize data ® time /
place / person
• Take immediate control
measures
• Formulate / test hypotheses
• Implement / evaluate
additional control measures
• Report findings
Public Health Emergencies
• Threat and reality of
bioterrorism have
focused attention on
public health
preparedness for
emergencies
• Planning for public
health emergencies
requires interagency
agreements, training,
and exercises
Public Health Emergencies
• Examples of public health
emergencies:
– Natural disaster:
hurricanes, floods,
earthquakes;
– Outbreaks from
contaminated food or
water, influenza
pandemics;
– Biological, chemical,
radiological and nuclear
WMD
What Should Make You Suspect an
Intentional Outbreak?
• Cases of an extremely rare disease (anthrax,
plague, smallpox) that could be BT agent
• Ordinary disease but out of season or area or
with wrong mode of spread or other unusual
characteristics (I.e. antibiotic resistance, atypical
symptoms or victim demographics)
• Cannot solve outbreak with usual techniques
• Threats received
• Group taking credit
• Plausible accusations
What Should Make You Suspect an
Intentional Outbreak?
• All victims attended a common event
• All victims share a common workplace or other
locale
• All victims work for the same agency
• A dissemination device is found
• Whom should PH workers call first in this
community when they receive allegations that
someone has caused an outbreak deliberately?
Categories of Intervention
• Efforts directed at source
of infectious agent
– Vehicle
– Vector
• Efforts directed at people
at risk
Poultry “Biosecurity”
USDA guidance to prevent
introduction/spread of A.I.
Interventions Directed at Source
• Eliminate / treat source
– Dispose of contaminated food, shock-chlorinate
contaminated water
• Isolate / treat infected persons
– Prevent further exposures by minimizing susceptible’
risk of exposure to infectious persons
• Close contaminated sites / sources
– Protect susceptible by minimizing risk of exposure
from infected sites / sources
Interventions Directed at
People at Risk
• Reduce risk of exposure
in susceptible people –
e.g., by educating on
how to avoid exposure
• Directly protect at-risk
people
– Vaccinate
– Post-exposure
treatment with
medicines or vaccines
to prevent or lessen
illness