OPTOMETRY · SEMESTER 2
Introduction To Epidemiology-2
Epidemiology and Biostatistics
Introduction to Epidemiology
Learning Objectives
- By the end of this session, students are expected to be able to:
- Define epidemiology, health and disease
- Describe Types of epidemiology
- Describe the application of epidemiology and achievements of epidemiology
- Explain the determinants of health and disease
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Epidemiology
- The word epidemiology comes from the Greek words
- epi = meaning on or upon
- demos = meaning people
- logos = meaning the study of or doctrine
- Thus the word “epidemiology” simply means the study of what is happening to people
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Definition od Epidemiology
- As per perkins 1873 it is that branch of science which treats epidemics
- As per frost 1927 it is the science of mass phenomenon of infection disease.
- As per greenwood 1934 the study of any disease as a mass phenomena
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Definition of 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. »
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Key words of the definition:
| Study | | Basic science |
| Distribution | | time, place, person |
| Determinants | | Cause, risk factors |
- Event Health status
| Population | | Community |
| Application | | Information for action |
Three closely-related components (distribution, determinants and frequency) encompass all epidemiological principles and methods
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Types of Epidemiology
DESCRIPTIVE EPIDEMIOLOGY
ANALYTICAL EPIDEMIOLOGY
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Distribution (DESCRIPTIVE EPIDEMIOLOGY)
- Distribution is concerned with the frequency and pattern of health events in a population
Distribution: Descriptive Epidemiology
- What, who, when, and where
- Frequency: number, rates, and risk
- Quantify diseases to determine magnitude
- Patterns: time, place, and person
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Distribution cont…
- Frequency: refers to the number of health events
- e.g.
- Number of cases of meningitis
- Number of cases of diabetes in a population
- Number of people with mental disorder in a population
- Number of children under one year of age vaccinated for measles
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Distribution cont…
Pattern of disease refers to the occurance of health related events or disease by time, place and person.
Time pattern may be; seasonal, annual, monthly, weekly, daily, hourly, weekends or weekdays.
Place pattern includes; residence (urban/rural), geographical variations, country variations Personal patterns includes; age, sex, gender, marital status, educational level
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Determinants (Analytic Epidemiology)
- Causes and influences
- Compare between exposure groups to determine causal relationships
- Evidence for control and prevention
- Why and how
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Definition of Health
- Health: A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity. (World Health Organization)
- Definition of Disease
- Disease: A disorder of structure or function in a human, especially one that produces
- specific symptoms or that affects a specific part.
- Definition of agent
- Is an microorganism/microbe that is cable of causing a disease
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Definition of host
| • | Host: An organism which harbors or nourishes another organism (parasite). |
| • | Intermediate host: An organism in which a parasite passes its larval or nonsexual existence. |
| • | Definitive host: An organism in which the parasite develops to an adult and sexually mature stage. |
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Host
- Host Is an organism capable of being infected by an agent.
- Examples…
- Host factors include:
- Age
- Sex
- Social class
- Personality
- Genetic factors
- Education
Marital status
Definition of vector
An organism which is capable of spreading infection by conveying pathogens from one host to another.
- vectors of medical importance
| i. | Mosquitoes |
| ii. | Tsetse flies |
| iii. | House flies |
| iv. | Ticks |
| v. | Mites |
| vi. | Bedbugs and Lice |
| vii. | Snails |
| viii. | Rodents |
| ix. | Fleas |
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Definition of Reservoir
Reservoir: The habitat in which disease-causing organisms normally live and multiply without necessarily being affected
- Reservoirs can be human, animal, or environmental.
- o Diseases with human reservoirs:
- Smallpox (symptomatic)
HIV (asymptomatic)
Diseases with animal reservoirs (also known as zoonoses):
- Brucellosis (can be found in goats, sheep, cattle, pigs)
- Plague (can be found in rats and other wild rodents)
- Anthrax (can be found in cattle, sheep, goats, and other herbivores)
- o Environmental
- Histoplasmosis (caused by a fungus that is often found in areas with lots of
- bird/bat droppings such as caves)
Legionnaires’ bacillus (caused by aquatic bacteria that grow in warm water)
- Note: a reservoir is different from a vector or disease carrier, which are agents of disease transmission.
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Agent
- An etiological factor which are necessary for
- bringing about a particular disease in a
- susceptible host.
- Examples of agents are:
- Plasmodium
- Yesinia pestis
Mycobacterium tuberculosis
The determinants of health include:
- Income and social status
- Education
- Physical environment
- Social support networks
- Biology and genetic endowment
- Health services (availability and accessibility)
- Gender
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In a Specified population how does epidemiologist differ from clinicians?
Epidemiologist and clinicians differ on how they view “the patient”.
Epidemiologist will be concerned with collective health of people in the community while clinician will focus on the individual case.
e.g. patient with diarrheal disease- what is source?, other people infected/exposed?, interventions to prevent additional cases > epidemiologist will take account
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Applications and Achievements of epidemiology
- Epidemiology is used to:
Describe the etiological factors in causation of disease.
Study the natural history of disease, from good health to subclinical changes until occurrence of clinical disease, where the outcome can be recovery (with or without disability) or death.
Describe the health status of populations, and the distribution of diseases in a population (in which the proportion of people with poor health changes with time and age) Provide and analyze information for planning, implementation and evaluation of health services; such as interventions directed at maintaining good health (including health promotion, prevention, and medical management of ill people through the provision of prompt treatment).
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• Non-communicable Diseases(NCDs)
Group of conditions that are not maily caused by an acute infection,result in long term health problems and often need long term treatment Examples;…………………………
- Chronic Diseases
Condtions that last 1 year or more and esquire ongoing medical attention or limit activities of daily living or both Examples……………………..
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Types of epidemiology
- There are mainly two types of epidemiology namely:-
- Descriptive (Distribution) epidemiology
- Analytical (Determinant) epidemiology
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Descriptive Epidemiology
Describe distribution of disease and health-related characteristics in the population.
Characterizing health events by time, place, and person are activities of descriptive epidemiology Formation of hypothesis (Case reports, case series, correlation studies)
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Examples of descriptive epidemiology
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Examples of descriptive epidemiologycont…
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Analytic Epidemiology
Identify and quantify the relationship between an exposure and a health outcome.
The hallmark of such a study is the presence of a comparison group (e.g. an outbreak of hepatitis A).
- Permit inferences about cause-and-effect relationships.
- Test the hypothesis (Case-control, cohort, experimental-studies)
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Analytical Epidemiologycont…
- Search for causes and effects, or the why and the how
Analytic epidemiology: quantify association between exposure and outcomes Studies (Experimental [clinical trial, community trial], cohort study, case-control study and sometimes cross sectional study used in analytical epidemiology)
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EVALUATION
- Which type of epidemiology can give answer to the following epidemiological questions
- What is the source of infection for an outbreak of diarrhoeal disease?
- What are the risk factors for neonatal tetanus in neonatal ward at Sokoine hospital?
- What factors are associated with increased mortality for persons with measles?
- Does smoking cause lung cancer?
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Key Points
As a discipline within public health, epidemiology includes the study of the frequency, patterns, and causes of health-related states or events in populations, and the application of the information gained to public health issues.
In epidemiology, our “patient” is the public at large—the community—and in “treating” our patient we perform several tasks, including public health surveillance, disease investigation, analytic epidemiology, and evaluation.
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Key points cont…
Epidemiology provides us with a systematic approach for determining What, Who, Where, When, and Why/How.
We use descriptive epidemiology to describe disease occurrence by person (Who), place (Where), and time (When).
We use descriptive epidemiology to portray the characteristics and public health of a population or community.
We use analytic epidemiology to sort out and quantify potential risk factors and causes (Why).
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aims/Uses/Applications of epidemiology
- Describe the distribution of diseases and burden in a population
Identification of etiological factors in pathogenesis Provide and analyze information for planning, implementation and evaluation of health status Study the natural history of disease
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Uses/Applications of epidemiology cont…
Make individual decisions e.g. quit smoking, climbing stairs vs. elevator, eat salad vs. chips or using condoms in casual sex
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Read on
- 5 Achievements in Epidemiology
- Epidemic communicable diseases
- Endemic communicable diseases
- pandemic diseases
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reference
Bety R. K., & Jonathan A. C. S. (2003) Medical Statistics (2nd Ed.), Massachusetts: Blackwell Publishing Company Herold JM. Surveys and sampling. In: Greg M, ed. Field epidemiology. 3rd ed. New York: Oxford University Press; 2008:97-117.
Keneth, J. R., Sander, G., & Timoth, L.L. (2008).Modem Epidemiology (3rd Ed.). Philladelphia: Lippincott Williams and Wilkins.
McCusker J. (2001). Epidemiology in Community Health, Rural Health Series No. 9 (Revised Edition). Nairobi, Kenya: AMREF Varkevisser et al. (1995). Designing and Conducting Health Systems Research Projects,
