Introduction to Epidemiology and Biostatistics Study Guide

Introduction to Epidemiology and Biostatistics

Instructor: MR. Mahundi E, MPHARM.
Scope: This session provides an exhaustive introduction to the core principles of epidemiology and biostatistics, establishing their role in public health and clinical research.

Learning Objectives

At the end of this session, a student should be able to:
- Define epidemiology and its major subtypes.
- Understand the necessity of studying epidemiology.
- Identify factors that contribute to disease transmission.
- Describe modes of disease transmission.
- Outline the fundamental steps in epidemiological investigation.

The Etymology and Fundamental Assumptions of Epidemiology

Etymology: The word "epidemiology" is derived from Greek roots:
- Epi: Upon.
- Demos: People.
- Logy: Study of.
Core Logic: It is the study of what falls "upon the people."
Fundamental Assumptions:
- Diseases (or other health events) do not occur at random.
- Diseases occur in specific population groups who are exposed in a particular way (termed "at risk").
- Diseases (or other health events) possess causal and preventive factors that are identifiable.
- Researchers can investigate these factors and apply the resulting knowledge to control the disease.

Defining Epidemiology and Key Terminology

Formal Definition (Last, 1988): "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."
Key Words and Conceptual Pillars:
- Study: Represents basic science and rigorous methodology.
- Distribution: Refers to the patterns of "Time, Place, and Person."
- Determinants: Refers to the "Causes and Risk Factors" involved.
- Event / Health Status: The specific condition or occurrence being tracked.
- Population: The focus is on public health groups rather than individual patients.
- Application: The use of information for action and intervention.

Health-Related Events in Epidemiology

Epidemic Communicable Diseases.
Endemic Communicable Diseases.
Non-communicable Diseases.
Chronic Diseases.
Injuries.
MCH (Maternal and Child Health).
Occupational and Environmental Health.
Health Behaviors.

Definitions and Types of Statistics

Public Perception: Statistics is often narrowly viewed as a collection of mathematical formulas.
Practical Definition: Information available in numerical form, including:
- Averages: For example, the average number of new daily admissions may be $43.4$ patients.
- Rates in Vital Statistics: For example, the Maternal Mortality Ratio (MMR) is $578$ per $100,000$ live births.
- Proportions: For example, the percentage of pregnant mothers who use Insecticide-Treated Nets (ITNs) is $65\%$ .
Subfields of Statistics:
- Descriptive Statistics: Deals with the systematic collection, summarization, and presentation of data.
- Inferential Statistics: Deals with drawing conclusions about a whole population based on a subset (sample) of that population. Example: Determining if there is a "significant difference" in response rates between chloroquine and Sulfadoxine-Pyrimethamine (SP).
Biostatistics: The specific application of statistics to the biological sciences.

Rationale for Studying Epidemiology and Biostatistics

The number of new products in the medical field is increasing rapidly.
Necessary for the design and conduct of scientific research.
Facilitates critical appraisal of literature and cost-effective analysis.
Enables the sharing of accurate information with prescribers.
Crucial for interpreting and evaluating medical and health information.

Distribution: Descriptive Epidemiology

Focus: Determining "What" is happening.
Frequency: Measuring the magnitude of disease through numbers, rates, and risk quantification.
Patterns: Identifying "When, Where, and Who" (Time, Place, and Person).

Determinants: Analytic Epidemiology

Focus: Determining "Why" and "How."
Investigation: Identifying causes and influences behind health events.
Goal: Providing the evidence required for control and prevention.
Methodology: Comparing exposure groups to establish causal relationships.

Historical Case Study: John Snow and the London Cholera Outbreak (1854)

Contribution: John Snow is a foundational figure in epidemiology due to his work on the Cholera epidemics.
Methodological Tools Used:
- Linelist.
- Spot Map (mapping cases to specific locations).
- Epidemic Curve.
- Tables categorized by district and by individual household.
Significant Locations Mapped in the 1854 Outbreak:
- Broad Street (Location of the primary pump).
- Carnaby Street.
- Marshall Street.
- Regent Street.
- Great Pulteney Street.
- Berwick Street.
- Silver Street.
- Poland Street.
- Golden Square.
- Brewery and Work House sites.
- Specific Pumps (A, B, C).

The Epidemiologic Triad

The triad consists of the interaction between three factors: Agent, Host, and Environment.

1. Host Factors

Host factors influence the chance for disease or the severity of the illness.
Physiologic Factors: General physical health status.
Genetic Factors: Inherited predispositions.
Immunologic Factors: Resistance or susceptibility to agents.
Behavioral Factors: Actions taken by the individual.
Demographics: Age, Sex, Race/Ethnicity, Marital Status, Religion, Socioeconomic Status (SES), Nutrition, Co-morbidity.

2. Agent Factors

The agent is necessary for the disease to occur.
Types of Agents:
- Infectious: Microorganisms (bacteria, viruses).
- Toxic: Chemical substances, toxins, tobacco, alcohol, drugs.
- Nutritional: Lack of or excess of specific nutrients.
- Physical: Trauma, radiation, fire.
Note: Some diseases are classified as having no single identifiable agent.

3. Environmental Factors

The environment encompasses external conditions that affect the transmission of the agent to the host.
Physical: Air quality, weather, noise, food, and water sources.
Biologic: Presence of disease vectors.
Socioeconomic / Physical Surroundings: Population density, substances in the workplace.
Special Environments: Hospitals, day-care centers, institutions, bath houses, crack houses, refugee camps.

Modes of Disease Transmission

Direct Transmission:
- Contact: Examples include Cutaneous Anthrax and hookworm.
- Droplet: Examples include Tuberculosis (Tb).
Indirect Transmission:
- Airborne: Examples include Histoplasmosis and Inhalation Anthrax.
- Vehicleborne: Transmission via food or water, such as Salmonella.
- Vectorborne (Mechanical): Transmission via insect appendages (e.g., Shigella carried by flies).
- Vectorborne (Biological): Transmission where the agent undergoes a life cycle change in the vector (e.g., Malaria).

Levels of Disease Frequency

Sporadic: Occasional, isolated cases.
Endemic: The constant presence and/or usual prevalence of a disease in a geographic population.
Epidemic: A sudden increase in the number of cases of a disease above what is normally expected in that population in that area.
Pandemic: An epidemic that has spread over several countries or continents, usually affecting a large number of people.

Basic Epidemiologic Methods and the "3 Steps"

Methodological Workflow:
1. Count cases (events).
2. Define the involved population.
3. Determine rates and proportions.
4. Compare rates.
5. Make inferences.

Step 1: Counting (Descriptive)

Determining the number of events or conditions in populations or subgroups.
Asks: "How many persons experienced a particular condition?"
The count serves as the Numerator.

Step 2: Dividing (Descriptive)

Dividing the number of events by the number of persons at risk in the population to establish a rate.
Asks: "What group of persons experienced the event?"
The population group serves as the Denominator.
Used to calculate proportions, rates, and odds.

Step 3: Comparing (Analytic)

Comparing rates from different populations to make inferences about possible causes for observed differences.
Study Designs:
- Cohort Study: Compares exposed vs. non-exposed individuals.
- Case-Control Study: Compares sick (cases) vs. healthy (controls) individuals.
Metrics:
- Rate Ratios or Rate Differences.
- Odds Ratios (Comparison of odds).
Outcome: Identifying risk factors and using statistical tests to determine the reliability of the differences.

The Purpose and Utility of Epidemiologic Studies

Comparison: Epidemiology is fundamentally based on making comparisons between groups with different characteristics or risk factors.
Health Planning: Epidemiology helps to:
1. Determine the magnitude and trends of health issues.
2. Identify the etiology or cause of disease.
3. Determine the mode of transmission.
4. Identify risk factors or susceptibility.
5. Study the natural history of diseases.
6. Determine the role of the environment.
7. Evaluate the impact of control measures.
8. Provide necessary information for health planning.

Practical Examples and Data Presentation

Hang-gliding Accident Case Study:
- Analyzes the number of accidents according to the time of day (Morning, Mid-morning, Mid-afternoon, Evening).
- Distinguishes between Male and Female victims.
- Highlights the importance of appropriate data grouping to identify if specific times or genders represent higher risk.
Drug Efficacy Testing:
- Example setup: A researcher conducts an experiment comparing "Drug A" and "Drug B."
- Patients are tested to evaluate the efficacy of the drugs.

Questions & Discussion

The transcript presents a hypothetical evaluation of data presentation: "What is inappropriate here?" regarding the hang-gliding chart, prompting students to think critically about whether the data are represented as raw counts or rates, and if proper denominators are used to draw conclusions.