Basic Epidemiological concepts Dr.Haitham Issa Al – Banna Assistant professor Hawler college of Medicine

EPIDEMIOLOGY Greek: EPI - Upon DEMOS - People LOGOS - Study of, Body of Knowledge

History of Epidemiology

Hippocrates (460-377 B.C.) On Airs, Waters, and Places Idea that disease might be associated with physical environment

Edward Jenner (1749-1823) Pioneered clinical trials for vaccination to control spread of smallpox  Jenner's work influenced many others, including Louis Pasteur who developed vaccines against rabies and other infectious diseases

Ignas Semmelweis (1840’s) Pioneered handwashing to help prevent the spread of septic infections in mothers following birth 

John Snow (1813-1858) Father of epidemiology Careful mapping of cholera cases in East London during cholera epidemic of 1854 Traced source to a single well on Broad Street that had been contaminated by sewage

Why is epidemiology the basic science of public health? PUBLIC HEALTH WORKS BY: • Defining a health problem • Identifying risk factors associated with the problem • Developing and testing community-level interventions to control or prevent the causes of the problem • Implementing interventions to improve the health of the population; and • Monitoring those interventions to assess their effectiveness

DEFINITIONS OF PUBLIC HEALTH • The science and art of : 1) preventing disease 2) prolonging life and 3) promoting health and efficiency through organized community effort.

Epidemiology asks or uses: Person- Who? Place- Where? Time- When? Helps us to understand: Why?

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 control of health problems.

Introduction to Epidemiology Key words Study Distribution Determinants Health-related states Populations Application

Epidemiology key words: Study Epidemiology is the basic science of public health. It's a highly based on principles of statistics and research methodologies.

Epidemiology key words: Distribution Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population. They use descriptive epidemiology, which characterizes health events in terms of time, place, and person. Questions: who, where, when

Epidemiology key words: Determinants Epidemiologists also attempt to search for causes or factors that are associated with increased risk or probability of disease. What factors cause the problem or are associated with the problem Questions: how and why

Epidemiology key words: Health-related states Epidemiology is applied to the whole spectrum of health-related events: chronic diseases, environmental problems, behavioral problems, injuries, infectious diseases.

Epidemiology key words: Populations One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients.

Epidemiology key words: Application . Epidemiological data aids in developing and evaluating interventions to control and prevent health problems.

Clinician Epidemiologist Patient’s Community Diagnosis Predict trend Therapy Control Cure Prevention

Objectives of epidemiology (uses of epidemiology) 1- Assessment of the health situation Collect basic data about diseases and health-related problems in the community 2- Study natural history and etiology of disease Help understand risk factors and natural history of disease 3- Control and prevention Provide recommendations for control and prevention of health problems in the population

4- Planning health interventions Provide data for developing health policy and sound planning 5- Evaluation of health interventions Assess the impact of health programs and interventions

Kinds of Epidemiology Descriptive Analytic

The Basic Triad Of Descriptive Epidemiology THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY: TIME PLACE PERSON

Descriptive Epidemiology Study of the occurrence and distribution of disease Terms: Time Place Person

Time Changing or stable? Seasonal variation. Clustered (epidemic) or evenly distributed (endemic)? Point source or propagated.

Time Secular Periodic Seasonal Epidemic

Secular Trend The long-time trend of disease occurrence

Tetanus – by year, United States, 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. Reported Cases

4. Disease incubation period Epidemic curve A graph of the time distribution of epidemic cases. An epid. Curve can suggest: 1- Time trend A time relationship with exposure to a suspected source. 2- Pattern of spread: A cyclical or seasonal pattern suggestive of a particular infection, and common source or propagated spread of the disease. 3. Magnitude 4. Disease incubation period

Periodic Trend Temporal interruption of the general trend of secular variation

Whooping Cough - Four-monthly admissions, 1954-1973

Seasonal Trend

4. Disease incubation period Epidemic curve A graph of the time distribution of epidemic cases. An epid. Curve can suggest: 1- Time trend A time relationship with exposure to a suspected source. 2- Pattern of spread: A cyclical or seasonal pattern suggestive of a particular infection, and common source or propagated spread of the disease. 3. Magnitude 4. Disease incubation period

Epidemic An increase in incidence above the expected in a defined geographic area within a defined time period

Endemic vs. Epidemic No. of Cases of a Disease Epidemic Endemic Time

Place Geographically restricted or widespread (pandemic)? Relation to water or food supply.   Multiple clusters or one?

Place Where patient was exposed or Where source became infected

Person Age Socio-economic status Gender Ethnicity/Race Behavior

Analytic Epidemiology Further studies to determine the validity of a hypothesis concerning the occurrence of disease.

The Basic Triad Of Analytic Epidemiology THE THREE PHENOMENA ASSESSED IN ANALYTIC EPIDEMIOLOGY ARE: HOST Define host, agent? AGENT ENVIRONMENT

Agents Nutrients Poisons Allergens Radiation Physical trauma Microbes Psychological experiences

Host Factors Genetic susceptiblity Immunologic state Age Personal behavior

Environment Crowding Atmosphere Modes of communication – phenomena in the environment that bring host and agent together, such as: Vector Vehicle Reservoir

Other different important definitions

Incidence Measure of new cases of disease (or other events of interest) that develop in a population during a specified period of time E.g. Annual incidence Measure of the probability that unaffected persons will develop the disease Used when examining an outbreak of a health problem

Prevalence Number of existing cases of disease or other condition Proportion of individuals in a population with disease or condition at a specific point of time Diabetes prevalence, smoking prevalence Provides an idea of how severe a problem may be – measures overall extent Useful for planning health services (facilities, staff)

Relationship Between Incidence and Prevalence Prevalence varies directly with both incidence and duration. If incidence is low, but duration is long (chronic), prevalence will be large in relation to incidence. If prevalence is low because of short duration (due to recovery, migration or death), prevalence will be small in relation to incidence.

Morbidity – illnesses, symptoms, impairments Mortality - deaths Acute disease – diseases that strike and disappear quickly, within a month or so (chicken pox, colds) Chronic disease – long term or lifelong diseases, incurable

Epidemiologic Measures

Tools Count العدد Rate المعدل Proportion التناسب Ratio النسبة

Count العدد

Why is a simple count not enough? 3 cases of cancer per year from a city of 1,000 people is very different than 3 cases per year from a city of 100,000 people

So, in epidemiology we must know: the size of the population from which the affected individuals come, and the time period the information was collected.

Example of proportion:

RATIO A fraction in which the numerator is not part of the denominator. e.g. Fetal death ratio: Fetal deaths/live births. Fetal deaths are not included among live births, by definition.

Ratio & Proportion Female All Female Male Ratio Proportion

Maternal mortality ratio- Number of maternal deaths ascribed to childbirth. Reflects health care access   Number of deaths assigned causes related to child birth maternal = x 100,000 live births mortality ratio Number of live births

Rate Special form of proportion that includes a specification of time Most commonly used in epidemiology because it most clearly expresses probability or risk of disease or other events in a defined population over a specified period of time 2 major types Crude rates Specific rates (age-specific, infant mortality)

Rate The basic formula for a rate is as follows: Number of cases or events occurring during a given time period Rate = Population at Risk during the same time period X 1000

Epidemic investigation Rule of six: Max. 6 words in a line and 6 lines/slide

Endemic vs. Epidemic No. of Cases of a Disease Epidemic Endemic Time

Outbreak Detection and Response First Case Detection/ Reporting Lab Confirmation Response DAY CASES Opportunity for control

Outbreak Detection and Response First Case Detection/ Reporting Confirmation Investigation Opportunity for control Response DAY CASES

objectives of an epidemic investigation 1- To define the magnitude of the epidemic in terms of time, place and person. 2- To determine the particular factors responsible for the occurrence of the epidemic. 3- To identify the cause, source(s) of infection, and modes of transmission to determine measures necessary to control the epidemic. 4-To make recommendations to prevent recurrence. Rule of six: Max. 6 words in a line and 6 lines/slide

The elements of epidemic control include: 1. Controlling the source of the pathogen (if known) Remove or inactivate the pathogen 2. Interrupting the transmission Sterilize environmental source of spread and vector control 3. Controlling or modifying the host response to exposure, Immunize the susceptible; use prophylactic chemotherapy