COURSE UNIT 9: INTRODUCTION AND BASIC • Programs to remove filth likewise put up to serve

CONCEPTS OF EPIDEMIOLOGY to advance community sanitation.

Germ or Bacteriological Theory
INTRODUCTION TO EPIDEMIOLOGY • Koch confirmed Pasteur’s previous claims
• Disease is due to microscopic forms of life
Definition: Epidemiology • Opened the concepts of isolation and quarantine
The study of the distribution and determinants of health, • Measures to destroy and remove the
disease, or injury in human populations and the bacteriological cause such as disinfection ,
application of this study to the control of health problems. fumigation and general cleanliness
• Bacteriology – explained the origins and spread of
PURPOSES IN PUBLIC HEALTH PRACTICE communicable disease
• Discover the agent, host, and environmental Henle-Koch's postulates (1877,1882)
factors that affect health Koch stated that four postulates should be met before a
• Determine the relative importance of causes of causal relationship can be accepted between a particular
illness, disability, and death bacterial parasite (or disease agent) and the disease in
• Identify those segments of the population that question. These are:
have the greatest risk from specific causes of ill 1. The agent must be shown to be present in
health every case of the disease by isolation in pure
• Evaluate the effectiveness of health programs and culture.
services in improving population health 2. The agent must not be found in cases of
other disease.
SOLVING HEALTH PROBLEMS 3. Once isolated, the agent must be capable of
Step 1. Data collection: Surveillance; determine reproducing the disease in experimental
time, place, and person animals.
Step 2. Assessment: Inference 4. The agent must be recovered from the
Step 3. Hypothesis testing: Determine how and why experimental disease produced.
Step 4. Action: Intervention
Concept of Multiple causation
• Disease results from the interaction of
DISEASE CAUSATION multiple ecologic factors within a dynamic
Theories of Disease Causation system made up of an agent of disease ,
• Disease was due to evil spirits host and the environment
• Recovery was attributed to good spirits
• Disease as a form of punishment MODELS OF DISEASE CAUSATION
• Control measures include offering sacrifices and
“casting-out demons” 1) The Web
Filth Theory States that effects never depend on single isolated causes
• Associates disease with the physical environment but rather develop as the result of chains of causation. It is
• Disease change with seasons, climate, a result of complex genealogy and antecedents
temperature, overcrowding and filth
• Diseases were due to poisonous substances and
gases from the earth
“Bad air”
• was the cause of fever .
• Building huge fires can purify the air
 • The characteristic of the two are influenced
considerably by the conditions of their environment

3) The Epidemiologic Triangle

• It is consist of 3 Components: the Host, the Agent
and the Environment. Each of the component
must be considered for better understanding and
Web of Causation for Myocardial Infarction prediction of patterns of disease.

ENVIRONMENTAL FACTORS OF DISEASE

THE ENVIRONMENT
These are external to the host and in which the agent may
exist, survive, or originate. It can be physical, climatologic,
biologic, social and economic

Physical:
– water, humidity, geologic formations, etc

Social:
2) The Epidemiologic Lever
– characteristics of a group of people
• The host and agent are at the opposite ends of a
It may enhance or diminish survival of agent. It may
hypothetical lever while the environment serves as
also serve to bring agent and host into contact. A
the fulcrum.
reservoir is a medium that fosters the survival of
infectious disease agent.
Based on biologic laws:
• Disease results from an imbalance between disease
An individual or animal infected with a pathogenic microbe
agent and man
is called a Reservoir host. Human reservoir hosts can be
• The nature and extent of the imbalance depends on patients, personnel, or visitors and include those with an
the nature and characteristics of the host and the active disease, those incubating a disease, and chronic
agent carriers of a disease.
 “Progression of a disease process in an individual over
THE AGENT FACTOR OF DISEASE time, in the absence of treatment” (CDC)
An agent is any element, substance, or force whether
living or non-living, the presence or absence of which can
initiate or perpetuate a disease process.

Characteristics of Agents of Diseases

• Inherent Characteristics
o Physical Features
o Biologic Requirements

• Characteristics directly related to man

o Infectivity - the ability of an agent to invade
and multiply in a host.
o Pathogenicity - the ability to produce clinically
apparent illness.
TWO PHASES
o Virulence - severity of the reaction produced
and measured in terms of fatality 1) PREPATHOGENESIS
o Immunogenicity - infections ability to produce • Phase before man is involved
specific immunity Through interaction of agent, host and
environmental factors, agent finally
• Characteristics related to the environment reaches man
o Reservoir Risk factors
o Sources of infection • Poor health and nutrition
o Modes of transmission • Lack of immunity
- Refer to the mechanisms by which an • Behaviors that increase opportunity
infectious agent is transported from for exposure
reservoir to susceptible human host
- There are three modes of pathogen
transmission:
a. Contact transmission
b. Vehicle transmission
c. Vector transmission
2) PATHOGENESIS
THE HOST • Includes the success invasion and establishment
The host goes through chain of events leading from of the agent in the host
unapparent infection to a clinical case of the disease. • From incubation period to production of detectable
Severity of illness depends on resistance of the host evidence of the disease process (Clinical
(immunity level). End result of infection: Horizon), until it is interrupted by treatment
– complete recovery
– permanent disability/disfigurement
– death
– chronicity
NATURAL HISTORY OF THE DISEASE
Pathogenesis Secondary Prevention
• Early detection
• Prompt treatment
• Cure disease at the earliest stage

Tertiary Prevention
• Complete treatment
• Limit disability
Sub-clinical stages of disease Incubation period • Rehabilitation
• Asymptomatic
• Time between exposure to onset of symptoms SOURCES OF EPIDEMIOLOGIC DATA
• Infectious diseases Considerations in Choosing the Source of Data
• Research Objective
Latency period • Data Quality
• Asymptomatic • Sensitivity Issues
• Time between exposure to causal factor and • Logistics
disease detection
• common in Non-Communicable Diseases General Types of Data
Primary Data: collected by the researcher first-hand
Stage of Clinical Disease Queries
• Refers to the period of time at the onset of signs • Interviews
or symptoms of the disease. Sufficient end-organ • Questionnaires
changes have occurred so that there are • FGD
recognizable signs or symptoms of disease. The Observations
clinical stage of different diseases differs in • Direct
duration, severity and outcome. The outcomes of • With tools
this stage may be recovery, disability or death.
Secondary Data: derived from another source that may
Outcome of the Disease have other objectives for collecting the data
• The final stage in the natural history of disease Computerized bibliographic databases and Surveillance
concerns the outcome: recovery, disability or data: Census, Registries, Hospital records, Insurance
death records

Levels of Prevention TERMINOLOGIES:

• Primordial – Before risk factors • Asymptomatic- A condition or a person producing
• Primary - Pre-pathogenesis or showing no symptoms
• Secondary – Subclinical or very early clinical • Chronicity- Having an illness persisting for a long
• Tertiary - Middle to late clinical time or constantly recurring
• Rehabilitation- The action of restoring someone to
Primordial Prevention health or normal life through training and therapy
Prevent development of risk factors • Susceptibility- The state of being predisposed to,
sensitive to, or of lacking the ability to resist
Primary Prevention something (ie. disease, pathogen).
Prevent disease:
• Reduction of risk factors
• Immunization PART II COURSE UNIT 9:
• Removal of harmful agents SOURCES OF EPIDEMIOLOGIC DATA
Health Indicators: • Small number of health questions that can be
included
2) Civil Registry
• Primary purpose: establishment of legal
documents as required by law
• Major and most effective source of vital statistics
• **Cause of death together with ICD
• Advantage
• Enables the routine production of vital
statistics essential for improving health
outcomes, as well as the provision of
small-area data
• Disadvantage
• In low and lower-middle-income countries,
civil registry is weak or non-existent
Considerations in Choosing the Source of Data 3) Birth Statistics
• Research Objective • Most visible evidence of a government’s existence
• Data Quality of a person as a member of the society
• Sensitivity Issues • Uses of birth certificate data:
• Logistics a. Calculation of birth rates
General Types of Data b. Maternal conditions, length of gestation, birth
• Primary Data: collected by the researcher weight, congenital abnormalities..
firsthand • Problems: completeness of entries, unreliable
• Secondary Data: derived from another source that data from the mother, neonatal defects
may have other objectives for collecting the data undetected at birth
Data Sources according to Type of Data 4) Death Statistics
Primary • Mortality data have the advantage of being almost
A. Queries totally complete because deaths are unlikely to go
• Interviews unrecorded
• Questionnaires • **Cause of Death
• FGD o Immediate cause of death: final disease,
B. Observations injury, complication
• Direct o Antecedent cause of death: intervening
• With tools event between immediate and underlying
Secondary cause of death
A. Computerized bibliographic databases o Underlying cause of death: disease that
B. Surveillance data initiated chain of morbid events
• Census • Uses of death certificate:
• Registries o Calculation of mortality rates
• Hospital records o Information on CoD
• Insurance records Problems:
Secondary: o Correctness of entries
1) Census o Stigma associated with certain illnesses
Advantage o Lack of standardization of diagnostic
• Info on population numbers and distributions by criteria
age, sex and others o Change of coding for CoD over time
• Allows small-area estimation and disaggregation Notifiable Disease Statistics
like socio-economic status • Reportable diseases
Disadvantage
 o Selected for being epidemic-prone • Food and agricultural records
o Targeted for eradication or elimination • Occupational reports
o Subject to international health regulation • Police records
USES:
o Monitor progress towards disease DATA QUALITY AND UTILITY
reduction targets • Nature of the data
o Measure achievements of disease • Vital statistics, registries, surveys
prevention activities • Availability of the data
o Identify hidden outbreaks or problems so • Accessibility to the researcher
• Completeness of population coverage
that early action may be taken
• Representativeness
• Vale and limitations
Notifiable Diseases
• usefulness
• Category 1
• acute flaccid paralysis, anthrax, adverse
DATA PRIVACY AND CONFIDENTIALITY
event following immunization, human
• Privacy vs. Confidentiality ?
avian influenza, measles, meningococcal
• Republic Act 10173: Data Privacy Act of 2012
disease, neonatal tetanus, paralytic
• Executive Order No. 2 s. 2016: Freedom of
shellfish poisoning, rabies, SARS,
Information
outbreaks, clusters of diseases, unusual
diseases or threats
SENSITIVE PERSONAL INFORMATION (RA 10173)
• Category 2
• Individual’s race, ethnic origin, marital status, age,
• Acute blood diarrhea, acute encephalitis,
political affiliations, etc.
acute hemorrhagic fever, acute viral
• Individual’s health, education, genetic or sexual
hepatitis, bacterial meningitis, cholera,
life of a person, etc.
dengue, diptheria, influenza-like,
• Issued by government agencies like SSS number,
leptospirosis, Malaria, Non-neonatal
licenses, tax returns, etc.
tetanus, pertussis, typhoid and
paratyphoid fever
DATA SHARING
• Voluntary release of information by one
POPULATION (SAMPLE) SURVEY
investigator or institution to another for purposes
Advantage
of scientific research
• Prime data sources on risk factors
• Advantage: enhancement of knowledge
• Possible to generate important data on the links
• Issues:
between health and socio-economic determinants
• Loss of control over intellectual property
Disadvantage
• Loss of privacy and confidentiality of the
• Less efficient in rare events
research subject
• Sampling error
• Estimates for local areas may not be possible
DATA LINKAGE
• Joining data from two or more sources
INSTITUTION-BASED SURVEILLANCE DATA
• Requires interoperability of data sources
1) Within the Health Sector
• Talk with each other
• Case reporting
• Use of common identifying features to
• Morbidity and mortality data
connect data records on a single
• Availability and quality of services
individual
• Services delivered and commodities
provided
• Resources
2) Beyond the Health Sector