Epidemiology made easy A guide for healthcare workers

[Audio] Epidemiology made easy A guide for healthcare workers Vid 1.

[Audio] Module 2 Introduction to Epidemiology Why does a disease develop in some people and not in others? What are the specific objectives of epidemiology? Epidemiology is the study of the distribution and determinants of health related states or events (including disease) in specified populations, and the application of this study to the control of health problems. Why does a disease develop in some people and not in others? That’s one of the core questions in epidemiology and a powerful one. The answer lies in a complex interaction of multiple factors. Disease doesn’t occur randomly ,it results from the interplay between: 1. Host Factors (the person) These are individual characteristics that influence susceptibility or resistance to disease: Genetics (for example, B-R-C-A mutations for breast cancer) Age Sex Immune status Nutritional status Underlying conditions (for example, diabetes) Some people are biologically more vulnerable. 2. Environmental Factors Conditions outside the individual that influence exposure to disease causing agents: Air and water quality Housing and sanitation Occupational exposures Climate Social environment (for example, poverty, stress) Environment affects both exposure risk and health outcomes. 3. Agent Factors These are the causes of disease, which vary by disease type: Infectious agents: Bacteria, viruses, parasites Chemical agents: Toxins, pollutants Physical agents: Radiation, trauma Lifestyle factors: Smoking, alcohol, diet Not everyone exposed to an agent develops disease — it depends on dose, duration, and host vulnerability. 4. Behavioral and Lifestyle Factors Choices that impact disease risk: Diet Physical activity Smoking Alcohol use Health seeking behavior (for example, screening, vaccination) These are modifiable risk factors a key focus of prevention. 5. Interactions Matter Often, disease develops when multiple risk factors come together. Example: Not everyone exposed to H-P-V develops cervical cancer risk increases with persistent infection, smoking, and genetic susceptibility..

[Audio] Why does a disease develop in some people and not in others? That’s one of the core questions in epidemiology and a powerful one. The answer lies in a complex interaction of multiple factors. Disease doesn’t occur randomly ,it results from the interplay between: 1. Host Factors (the person) These are individual characteristics that influence susceptibility or resistance to disease: Genetics (for example, B-R-C-A mutations for breast cancer) Age Sex Immune status Nutritional status Underlying conditions (for example, diabetes) Some people are biologically more vulnerable. 2. Environmental Factors Conditions outside the individual that influence exposure to disease causing agents: Air and water quality Housing and sanitation Occupational exposures Climate Social environment (for example, poverty, stress) Environment affects both exposure risk and health outcomes. 3. Agent Factors These are the causes of disease, which vary by disease type: Infectious agents: Bacteria, viruses, parasites Chemical agents: Toxins, pollutants Physical agents: Radiation, trauma Lifestyle factors: Smoking, alcohol, diet Not everyone exposed to an agent develops disease — it depends on dose, duration, and host vulnerability. 4. Behavioral and Lifestyle Factors Choices that impact disease risk: Diet Physical activity Smoking Alcohol use Health seeking behavior (for example, screening, vaccination) These are modifiable risk factors a key focus of prevention. 5. Interactions Matter Often, disease develops when multiple risk factors come together. Example: Not everyone exposed to H-P-V develops cervical cancer risk increases with persistent infection, smoking, and genetic susceptibility..

[Audio] This study is a large scale epidemiological analysis of breast cancer among women in the Eastern Province of Saudi Arabia, conducted at King Fahad Specialist Hospital Dammam. It explores how age, genetics, lifestyle, and environmental factors intersect to increase breast cancer risk—especially in younger Saudi women, who are diagnosed at a significantly earlier age than their Western counterparts. Using data from nearly 6000 breast cancer cases diagnosed between 2006 and 2022, the researchers investigated clinical features such as tumor stage, histological type, and hormone receptor status, alongside predictive models for future trends. The findings reveal a high prevalence of advanced stage diagnosis, a dominance of invasive ductal carcinoma, and a notable contribution of B-R-C-A mutations—particularly among younger women. This study highlights an urgent need for early screening programs, genetic testing, and lifestyle interventions tailored to the Saudi population, especially as breast cancer incidence is projected to double by 2028. Sample size: 5954 patients (2006–2022) Mean age at diagnosis: 49 years — significantly younger than Western countries Gender: 99% female Nationality: 92% Saudi nationals Most affected age group: 40–59 years (58% of cases) Stage at diagnosis: Regional: 47% Localized: 27% Distant metastasis: 19% In situ: 5% Most common subtype: Invasive Ductal Carcinoma (78%) Hormone receptor status: ER-positive: 61% PR-positive: 56% Her2-negative: 59% Regional Trends Highest referrals from Al Ahsa (31%), followed by Dammam (26%) and Khobar (13%) Age standardized incidence rate (A-S-I-R-) rose from 7 to over 50 per 100000 (2006–2021) Mortality rates remained relatively stable (~5–10 per 100000) Genetic and Lifestyle Factors High prevalence of BRCA1/2 mutations, particularly B-R-C-A-1 Contributing lifestyle factors: sedentary behavior, late childbearing, Western diet, reduced breastfeeding Cultural factors like consanguinity increase hereditary mutation risks.

[Audio] What are the specific objectives of epidemiology? First, to identify the etiology or cause of a disease and the relevant risk factors that increase a person’s risk for a disease. Second, to determine the extent of disease foundation in the community. Third, to study the natural history and prognosis of disease Fourth, to evaluate both existing and newly developed preventive and therapeutic measures and modes of health care delivery Fifth, to provide the foundation for developing public health policy relating to environmental problems, genetic issues and other considerations regarding disease prevention and health promotion..

[Audio] Examples of Research Areas Using Epidemiology ( vid 2) Examples of Research Areas Using Epidemiology Infectious disease outbreaks (for example, COVID-19, Ebola) Chronic diseases (for example, cancer, diabetes, cardiovascular disease) Environmental health (for example, pollution and asthma) Occupational health (for example, asbestos exposure and mesothelioma) Injury prevention Mental health Pharmacoepidemiology Genetic and Molecular Epidemiology.

[Audio] Epidemiology and prevention Public health is Multidisciplinary field that Promote the health of the population through organized community efforts. There are two aspects of public health where epidemiology is used. -First, prevention. -Second, interventions..

[Audio] Three levels of public health prevention Primary Prevention Prevent disease or injury before it occurs Vaccination (for example, polio, M-M-R--) Health education (for example, anti smoking campaigns) Safe water and sanitation Seatbelt laws Secondary Prevention Early detection and treatment to halt disease Cancer screenings (for example, mammograms, Pap smears) Blood pressure checks Diabetes screening Contact tracing Tertiary Prevention Reduce impact of ongoing illness or injury Rehabilitation (for example, after stroke) Chronic disease management (for example, insulin for diabetes) Support groups Surgery to prevent complications.

[Audio] What is the main goal of public health epidemiology? A-To treat individual patients B-To prevent disease and promote health at the population level C To diagnose infections in hospitals D To analyze D-N-A for genetic disease B.

[Audio] Public Health Intervention levels Individual Level Person or patient Change individual behavior or manage health One on one counseling (for example, smoking cessation) Vaccinations Personalized diet/exercise plans Health screenings Population Level (Community Level) Groups or entire populations Improve health outcomes at a societal level Public smoking bans Mass media campaigns Safe water and sanitation Health related laws (for example, seatbelt use).

[Audio] Measures of occurrence of Disease: Morbidity Vid 2.

[Audio] Measures of occurrence of Disease: Morbidity Incidence Cumulative Incidence against Incidence Rate Attack rate Prevalence Two Types of Prevalence In previous module we discussed what is epi and how it is linked to public health we also covered the levels of disease prevention In this module we will discuss how we use rats to express the extent of morbidity resulting from a disease and in next module we will turn to expressing the extent of mortality in quantitative terms Occurrence of disease can be measured using rates or proportions. Rates tell us how fast the disease is occurring in a population. Proportions tell us what fraction of the population is affected. In this module we will cover.

[Audio] Incidence Cumulative Incidence against Incidence Rate Is defined as the number of new cases of disease that occur during a specified period of time in population at risk for developing the disease Cumulative Incidence (C-I---) Incidence Rate (I-R---) Is defined as the number of new cases of disease that occur during a specified period of time in population at risk for developing the disease Cumulative Incidence (C-I---) Definition The proportion of at risk individuals in a population who develop the disease over a specified period of time. Unitless (a proportion, often expressed as a percentage). Assumes the entire population is followed for the entire period. Formula: Cumulative Incidence= Number of new cases during a period / Number of individuals at risk at the beginning of the period Incidence Rate (I-R---) The rate at which new cases occur in a population, accounting for the time each individual is at risk (person time). -Expressed as cases per person time (for example, 10 cases per 1000 person years). -Accommodates variable follow up time. Formula: Incidence Rate= Number of new cases / Total person time.

[Audio] Incidence Incidence rate The rate at which new cases occur in a population, accounting for the time each individual is at risk (person time). Formula: Incidence Rate= Number of new cases / Total person time Cumulative Incidence The proportion of at risk individuals in a population who develop the disease over a specified period of time. Formula: Cumulative Incidence= Number of new cases during a period / Number of individuals at risk at the beginning of the period.

[Audio] Use Incidence Rate when: Use Cumulative Incidence when: Participants are followed for different lengths of time (for example, some drop out) All participants are followed for the same time period You want to account for person time You want a simple estimate of risk over time The disease/event is rare or time dependent The disease/event occurs in a fixed time window.

[Audio] Examples In a population of 1000 people, if 50 develop a disease in one year what is the cumulative incidence ? CI=1000 / 50​=0.05 or 5% How to interpret ? Among the 1000 people at risk at the start of the year, 5 out of every 100 (or 1 in 20) developed the disease during the one year period How to Interpret the Cumulative Incidence: "Over the course of one year, 5% of the population developed the disease." Or more precisely: "Among the 1000 people at risk at the start of the year, 5 out of every 100 (or 1 in 20) developed the disease during the one year period.".

[Audio] Employee Time Followed (years) Outcome A 2.0 Stayed healthy B 1.5 Developed disease C 0.5 Left job early D 2.0 Developed disease E 1.0 Stayed healthy F 0.8 Developed disease Example 2 A company wants to track the incidence of a respiratory disease in a small group of 6 employees over a 2-year study period. Some employees leave early or get sick before the study ends. Here’s the follow up info: Calculate Total Person Time Count the Number of New Cases Calculate Incidence Rate Example 2 : A company wants to track the incidence of a respiratory disease in a small group of 6 employees over a 2-year study period. Some employees leave early or get sick before the study ends. Here’s the follow up info: Calculate Total Person Time Add up the follow up time for each person: Total Person Time=2.0 plus 1.5 plus 0.5 plus 2.0 plus 1.0 plus 0.8=7.8 person years Count the Number of New Cases From the table, these employees developed the disease: B D F Number of New Cases=3.

[Audio] Answers Calculate Total Person Time Add up the follow up time for each person: Total Person Time=2.0 plus 1.5 plus 0.5 plus 2.0 plus 1.0 plus 0.8=7.8 person years Count the Number of New Cases From the table, these employees developed the disease: B D F Number of New Cases=3 Calculate the Incidence Rate Incidence Rate (I-R---)=Number of New Cases / Total Person Time 3 / 7.8= 0.3846 per person year Convert to a standard rate (for example, per 1000 person years): 0.3846×1000=384.6 cases per 1000 person year Calculate Total Person Time Add up the follow up time for each person: Total Person Time=2.0 plus 1.5 plus 0.5 plus 2.0 plus 1.0 plus 0.8=7.8 person years Count the Number of New Cases From the table, these employees developed the disease: B D F Number of New Cases=3 Use the Incidence Rate Formula Incidence Rate (I-R---)=Number of New Cases / Total Person Time 3 / 7.8= 0.3846 per person year Convert to a standard rate (for example, per 1000 person years): 0.3846×1000=384.6 cases per 1000 person year.

[Audio] Attack Rate It measures the proportion of people who become ill after being exposed to a risk (for example, contaminated food, infectious person). Usually expressed as a percentage (%). It applies over a short period of time. Often used for foodborne illness, respiratory outbreaks, et cetera Formula: Attack Rate= Number of people at risk/Number of new cases of disease​ ×100 Attack rate Attack Rate is a type of cumulative incidence used in outbreak investigations and acute disease settings. It measures the proportion of people who become ill after being exposed to a risk (for example, contaminated food, infectious person). Usually expressed as a percentage (%). It applies over a short period of time. Often used for foodborne illness, respiratory outbreaks, et cetera Formula: Attack Rate= Number of people at risk/Number of new cases of disease​ ×100 Example: A dorm has 100 students. 40 students developed the flu during a 2-week outbreak. Attack Rate=40 / 100×100=40 Interpretation: 40% of dorm residents got the flu during the outbreak..

[Audio] Example: A dorm has 100 students. 40 students developed the flu during a 2-week outbreak. Attack Rate=40 / 100×100=40 Interpretation: 40% of dorm residents got the flu during the outbreak..

[Audio] Prevalence Two Types of Prevalence Point Prevalence Proportion of a population with the condition at a specific point in time. Period Prevalence Proportion of a population with the condition during a specific time period (for example, over 1 year). ForMULA: Prevalence=Total population / Number of existing cases​×100 (or per 1000/100000) Prevalence: Definition and Explanation Prevalence is a measure of how common a disease or condition is in a specific population at a particular point in time or over a specific period. Two Types of Prevalence Point Prevalence Proportion of a population with the condition at a specific point in time. Period Prevalence Proportion of a population with the condition during a specific time period (for example, over 1 year). Prevalence=Total population / Number of existing cases​×100 (or per 1000/100000).

[Audio] Example: Suppose you survey a population of 1000 people, and you find that 100 people currently have diabetes at the time of the survey? Prevalence=Number of existing cases / Total population ​=100/1000​=0.10 or 10% How to Interpret? At the time of the survey, 10% of the population had diabetes. Or: Out of every 10 people, 1 currently has diabetes. Suppose you survey a population of 1000 people, and you find that 100 people currently have diabetes at the time of the survey. How to Interpret Prevalence: "At the time of the survey, 10% of the population had diabetes." Or: "Out of every 10 people, 1 currently has diabetes.".

[Audio] Practice Qs : A school has 500 students. During an outbreak of gastroenteritis over a 1-week period: 60 students developed symptoms. 10 of those students were previously sick with gastroenteritis before the outbreak began. A follow up survey conducted later found that 75 students currently have gastroenteritis.

[Audio] Question 1: Calculate the cumulative incidence during the outbreak A 60 / 500 B (60 10) / 500 C 75 / 500 D 10 / 500 Question 2: What is the attack rate? A (60 / 500) × 100 B (75 / 500) × 100 C (50 / 500) × 100 D (10 / 500) × 100 Question 3: What is the point prevalence of gastroenteritis at the time of the survey? A 75 / 500 B 60 / 500 C 10 / 500 D (60 10) / 500 Question 4: What type of incidence does the outbreak illustrate? A Cumulative incidence B Incidence rate C Point prevalence D Attack rate Q1 Answer: B (60 10) / 500 = 50 / 500 = 0.10 or 10% Explanation: Only new cases count toward cumulative incidence. 10 students were already sick before the outbreak, so the new cases = 60 10 = 50. Q2 Answer: C (50 / 500) × 100 = 10% Explanation: The attack rate is essentially the cumulative incidence during an outbreak, used in acute settings. So it's 50 new cases / 500 at risk. Q3 Answer: A 75 / 500 = 0.15 or 15% Explanation: Prevalence measures existing cases at a specific time, regardless of when the disease began. At the time of the survey, 75 had the disease. Q4 Answer: D Attack rate Explanation: Since this was a short term outbreak of a disease in a defined population, the appropriate incidence type is attack rate, a form of cumulative incidence used in outbreaks..