BIOEPIDEMIOLOGY
LECTURE / FINALS / PPT-BASED
BIOE211
INTRODUCTION DISEASE CAUSATION
NATURAL HISTORY OF THE DISEASE
SOURCES OF DATA
HOST
 goes through a chain of events leading from
inapparent infection to a clinical case of the disease
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Sufficient Cause – Cause that inevitably
initiates or produces an effect  includes
“component causes”
Any given cause may be necessary,
sufficient, both, neither
GRADIENT OF INFECTION
TYPES OF CAUSAL RELATIONSHIPS
 Range of infection, from inapparent to severe
disease.
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Necessary and sufficient – without the
factor, the disease never develops
With the factor, disease always develops
(this situation rarely occurs)
THE HOST
 The severity of illness depends on the resistance
of the host (immunity level)
 end result of infection -- complete recovery -permanent disability/disfigurement -- death –
chronicity.
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CHARACTERISTICS OF THE HOST
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Non-specific Defense Mechanisms
• Skin
• mucosal surface
• Tears
• Saliva
• acid pH of gastric juice
• phagocytes & macrophages
• Age, nutrition status, genetic factors
Necessary but not sufficient – the factor
in and of itself is not enough to cause
disease.
Multiple factors are required, usually in a
specific temporal sequence (such as
carcinogenesis).
Sufficient but not necessary – the factor
alone can cause disease, but so can other
factors in its absence.
Benzene or radiation can cause leukemia
without the presence of the other.
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Neither sufficient nor necessary – the
factor cannot cause disease on its own, nor
is it the only factor that can cause that
disease
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This is the probable model for chronic
disease relationships
Other concepts related to causation
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Necessary versus Sufficient Cause
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Necessary Cause – Factor must be present
for the disease to occur it must invariably
precede an effect.
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HERD IMMUNITY
Immunity of a group or a community
“resistance” of a group to invasion and
spread of an infectious agent based on the
immunity of a high proportion of individual
members of the group
•important factor underlying the dynamics of
propagated epidemic
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BIOEPIDEMIOLOGY
LECTURE / FINALS / PPT-BASED
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NATURAL HISTORY OF THE DISEASE
TWO PHASES
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1. PREPATHOGENESIS
• The phase before man is involved.
• Through the interaction of agent, host, and
environmental factors, the agent finally
reaches man.
2. PATHOGENESIS
• Includes the successful invasion and
establishment of the agent in the host.
• From the incubation period to the
production of detectable evidence of the disease
process (Clinical Horizon), until it is interrupted by
treatment.
Natural History of Disease
“Progression of a disease process in an individual
over time, in the absence of treatment” --(CDC)
health determinant.
During this stage, the individual in the
population does not have the disease nor
the infection; only the risk factors are
present.
The susceptibility stage ends with effective
exposure.
PRE-PATHOGENESIS
Who is at Risk?
• Risk factors
• Poor health and nutrition
• Lack of immunity
• Behaviors that increase the opportunity for
exposure
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Adaptation
Failure leads to pathogenesis
Immediate response of the body
Immune system
STAGE OF PRESYMPTOMATIC DISEASE
(Sublinical stage)
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The etiological factors (e.g. infectious agent,
risk behaviors, environmental toxins) are
present in the body and are causing
pathological changes, but there are not yet
any discernible signs or symptoms.
•
In this stage there is no manifest of disease
but pathogenic changes have started to
occur.
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The time required for the agent to establish
itself, multiply and produce toxins
STAGE OF SUSCEPTIBILITY
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Pre-exposure period in the natural history of
the disease, in which the individual in the
population is vulnerable or at risk of
acquiring the infection and/or amenable to
getting exposed to and being harmed by a
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BIOEPIDEMIOLOGY
LECTURE / FINALS / PPT-BASED
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Sub-clinical stages of the disease
Incubation period
• Asymptomatic
• Time between exposure to onset of
symptoms of
• Infectious diseases
Morphologic subdivision or functional or
therapeutic considerations
STAGE OF DISABILITY
Latency period
• Asymptomatic
• Time between exposure to causal factors
and disease detection
• **common in NCD
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The final stage in the natural history of
disease concerns the outcome: recovery,
disability, or death.
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Some diseases run their course and then
resolve completely either spontaneously or
by treatment
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Any temporary or long-term reduction of a
person’s activities
PATHOGENESIS
STAGE OF CLINICAL DISEASE
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Refers to the period of time at the onset of
signs or symptoms of the disease.
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Sufficient end-organ changes have occurred
so that there are recognizable signs or
symptoms of the disease
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The outcomes of this stage may be
recovery, disability, or death.
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It is important to subdivide this stage for
better management of cases and purposes
of epidemiologic study
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BIOEPIDEMIOLOGY
LECTURE / FINALS / PPT-BASED
Levels of Prevention Primordial
• Before risk factors Primary
• Pre-pathogenesis Secondary
• Subclinical or very early clinical Tertiary
• Middle to late clinical
CLASSIFICATION OF DISEASES
Primordial Prevention
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Prevent the development of risk factors
SOURCES OF EPIDEMIOLOGIC DATA
Target:
❖ National Policies and Programs
❖ Mass Education
❖ Individual Education
Primary Prevention
❖ Prevent disease:
❖ Reduction of risk factors
❖ Immunization
❖ Removal of harmful agents
Target:
Secondary Prevention
❖ Early detection
❖ Prompt treatment
❖ Cure disease at the earliest stage
Considerations in Choosing the Source of Data
✓
✓
✓
✓
Target:
Tertiary Prevention
❖ Complete treatment
❖ Limit disability
❖ Rehabilitation
Primary Data: collected by the researcher firsthand
Secondary Data: derived from another source that
may have other objectives for collecting the data.
Target:
Classification of diseases
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Research Objective
Data Quality
Sensitivity Issues
Logistics General Types of Data
Method of grouping diseases based on their
specific features
Ensures universal criteria for diagnosing
diseases
Usually dependent on the current level of
knowledge about the disease
Data Sources according to Type of Data
Primary
A. Queries
• Interviews
• Questionnaires
• FGD
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B. Observations
• Direct
• With tools
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BIOEPIDEMIOLOGY
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Secondary
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Civil Registry: Birth Statistics
➢ The most visible evidence of a government’s
existence of a person as a member of the
society.
➢ Uses of birth certificate data:
Computerized bibliographic databases
B. Surveillance data
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Census
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Registries
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Calculation of birth rates
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Hospital records
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Insurance records
Maternal conditions, length of gestation, birth
weight, and congenital abnormalities.
➢ Problems: completeness of entries,
unreliable data from the mother, neonatal
defects undetected at birth
Secondary: Census
Advantage
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Info on population numbers and distributions
by age, sex, and others
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Allows small-area estimation and
disaggregation like socioeconomic status
Disadvantage
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Civil Registry: Death Statistics
➢ Mortality data have the advantage of being
almost totally complete because deaths are
unlikely to go unrecorded
The small number of health questions can be
included
➢ **Cause of Death
Secondary: Civil Registry
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Primary purpose: establishment of legal
documents as required by law
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Major and most effective source of vital
statistics
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**Cause of death together with ICD Civil
registry
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Immediate cause of death: final disease,
injury, complication
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Antecedent cause of death: intervening event
between immediate and underlying cause of
death
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The underlying cause of death: a disease
that initiated a chain of morbid events
Civil Registry: Death Statistics
➢ Uses of death certificate:
Advantage
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Calculation of mortality rates
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Information on CoD
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Enables the routine production of vital
statistics essential for improving health
outcomes, as well as the provision of smallarea data.
Disadvantage
In low and lower-middle-income countries, the civil
registry is weak or non-existent
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➢ Problems:
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Correctness of entries
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Stigma associated with certain illnesses
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Lack of standardization of diagnostic criteria
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Change of coding for CoD over time.
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BIOEPIDEMIOLOGY
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NOTIFIABLE DISEASE STATISTICS
➢ Reportable diseases
Disadvantage
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Less efficient in rare events
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Selected for being epidemic-prone
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Sampling error
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Targeted for eradication or elimination
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Subject to international health regulation
Estimates for local areas may not be
possible
➢ USES
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INSTITUTION-BASED SURVEILLANCE DATA
Monitor progress towards disease reduction
targets Measure achievements of disease
prevention activities.
Within the Health Sector
Identify hidden outbreaks or problems so that
early action may be taken
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Case reporting
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Morbidity and mortality data
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Availability and quality of services
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Services delivered and commodities
provided resources
Notifiable Diseases
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Category 1
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acute flaccid paralysis, anthrax, adverse
event following immunization, human avian
influenza, measles, meningococcal disease,
neonatal tetanus, paralytic shellfish
poisoning, rabies, SARS, outbreaks, clusters
of diseases, unusual diseases or threats
Beyond the Health Sector
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Food and agricultural records
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Occupational reports
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Police records
DATA QUALITY AND UTILITY
➢ Nature of the data
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Category 2
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Acute blood diarrhea, acute encephalitis,
acute hemorrhagic fever, acute viral
hepatitis, bacterial meningitis, cholera,
dengue, diphtheria, influenza-like,
leptospirosis, Malaria, Non-neonatal tetanus,
pertussis, typhoid and paratyphoid fever
➢ Availability of the data
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Vital statistics, registries, surveys
Accessibility to the researcher
➢ Completeness of population coverage
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Representativeness
➢ Vale and limitations
Population (Sample) Survey
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usefulness
Advantage
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Prime data sources on risk factors
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Possible to generate important data on the
links between health and socioeconomic
determinants
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BIOEPIDEMIOLOGY
LECTURE / FINALS / PPT-BASED
➢ Requires interoperability of data sources
Data Privacy and Confidentiality
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Privacy vs. Confidentiality?
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Republic Act 10173: Data Privacy Act of
2012.
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Executive Order No. 2 s. 2016: Freedom of
Information
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Talk with each other
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Use of common identifying features to
connect data records on a single individual.
Sensitive personal information (RA 10173)
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Individual’s race, ethnic origin, marital status,
age, political affiliations, etc.
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Individual’s health, education, the genetic or
sexual life of a person, etc.
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Issued by government agencies like SSS
numbers, licenses, tax returns, etc.
Data Sharing
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Voluntary release of information by one
investigator or institution to another for
purposes of scientific research
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Advantage: enhancement of knowledge
➢ Issues:
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Loss of control over intellectual property
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Loss of privacy and confidentiality of the
research subject
Data Linkage
➢ Joining data from two or more sources
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