Epidemiology - L1

Introduction to Epidemiology

• Epidemiology is derived from Greek words: epi (on or upon), demos (people), and logos (study of).
• It's the study of what happens to populations, specifically regarding health, including negative issues.

Definition of Epidemiology

• Epidemiology investigates diseases in different age groups and explores how, when, and why they occur in populations.

Background of Epidemiology

• Epidemiological methods emerged in the early 1800s to study disease occurrences.
• Early focus was on infectious (contagious) diseases.
• In the 1940s and 1950s, the study expanded to non-communicable diseases like heart attack and lung cancer.

Benefits of Epidemiological Information

• It helps plan and evaluate strategies to identify and prevent disease in at-risk individuals.
• It assists in managing patients who already have diseases.

Disease

• Disease is an abnormality affecting body structure or function, often associated with specific signs and symptoms.
• Two types: contagious (communicable) and non-contagious (non-communicable).

Injury

• Injury is physical harm or damage to the body.
• Injuries can be caused by accidents or overuse (repetitive) stress on body parts.
• Types include acute and overuse injuries.

Measuring Disease and Injury Occurrence

• Incidence: The number of new cases in a defined population during a specific time period. Measured by rate and proportion.
• Prevalence: Measures the total number of cases (old and new) in a population at a particular time. It has two types:
  • Point prevalence: The number of cases at a single point in time.
  • Period prevalence: The number of cases within a specified time period (e.g., a year).

Natural History of Disease

• Natural history describes the progression of a disease without treatment.
• It spans from the initial onset (inception) to recovery, disability, or death.
• Two phases: pre-pathogenic and pathogenic.

Pre-Pathogenic Phase

• During this phase, the individual isn't yet ill.
• The disease agent is present in the environment, but the host hasn't developed the disease yet.
• Epidemiological triad interaction (agent, host, environment)

Pathogenic Phase

• The disease agent enters the body, leading to clinically obvious or subtle disease.
• The natural history may lead to recovery, disability, or death.

Agents

• Agents can be living (e.g., bacteria, viruses, fungi) or non-living (e.g., chemicals, physical factors such as crushing, dislocation from accidents, nutritional factors such as excessive or deficient amounts of certain foods).

Host Factors

• Host factors include socio-demographic characteristics (e.g., age, gender, ethnicity, race), biological, social, and economic factors, life style.

Environmental Factors

• Environmental factors include physical aspects (e.g., air, soil, water), biological (e.g., co-existence with the ecosystem), and psychosocial (e.g., customs, habits, beliefs, religion).

Aetiology

• Aetiology is the study of the causes of diseases.
• It's divided into: intrinsic, extrinsic, and idiopathic (causes unknown).

Infectious Diseases

• Caused by viruses, bacteria, or fungi.
• Examples: common cold, flu, COVID-19, strep throat, whooping cough, gonorrhoea

Non-Infectious Diseases

• Not caused by external organisms, but related to genetics, anatomy, age, lifestyle. Examples include cardiovascular diseases, cancer, chronic respiratory diseases, diabetes.

Idiopathic

• Idiopathic refers to diseases with unknown causes.
• Also known as cryptogenic. Examples include scoliosis and frozen shoulder.

Risk Factors

• Risk is the probability of getting a disease.
• Understanding risk factors helps prevent diseases.
• Examples of common risk factors include obesity (risk of diabetes, heart attack, osteoarthritis), smoking (risk of cancers), and high blood pressure (risk of chronic pain, chronic obstructive lung disease).

Determinants of Disease

• Determinants are factors contributing to disease. Examples include age, gender, ethnicity, poverty, location, and occupation. These are often difficult for an individual to control.

Risk vs. Vulnerability

• What's the difference?