INTRODUCTION TO EPIDEMIOLOGY By Dr Mohammed Fawzi Associate Professor of Community Health Sciences Faculty of Applied Medical Sciences KSU, SA. Epidemiology 1 (CHS 334)

Objectives of this lecture: Defining health, public health and epidemiologyDefining health, public health and epidemiology Comparing between epidemiology & clinical medicineComparing between epidemiology & clinical medicine Recognizing key words in the definition of epidemiologyRecognizing key words in the definition of epidemiology Recognizing purposes of epidemiologyRecognizing purposes of epidemiology Describing characteristics of epidemiologyDescribing characteristics of epidemiology

Public health is primarily concerned with the prevention of disease in human population. It differs from clinical medicine in: its emphasis on prevention rather than treatment, its focus on populations rather than individual patients. Definitions of health states used by epidemiologists tend to be simple, "disease present" or "disease absent". The definition of health proposed by WHO in 1948 is "health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity".

There have been many definitions of epidemiology. The word epidemiology comes from the Greek words: epi, meaning “on” or “upon,” demos, meaning “people,” logos, meaning “the study of.” In other words, the word epidemiology has its roots in the study of what takes place in the population. Another definition is: “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.”

In the past 50 years or so, the definition has broadened from concern with communicable disease epidemics to take in all phenomena related to health in populations. The key feature of epidemiological studies is that they are: (rather than qualitative)quantitative (rather than qualitative) (rather than experimental)observational (rather than experimental) (rather than individuals).Carried out on determinants of diseases in human populations (rather than individuals).

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Epidemiology is the study of the distribution and determinants (factors) of health-related states or events in specified populations, and the application of this study to control of health problems. "Study" epidemiology is a study that includes surveillance, observation, hypothesis testing, analytic research, and experiments.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Epidemiology is the study of the distribution and determinants (factors) of health-related states or events in specified populations, and the application of this study to control of health problems. "Distribution“ epidemiologists study the distribution of frequencies and patterns of health events within a population. To do this, they use "descriptive epidemiology", which characterizes health events in terms of: time (when), place (where), persons affected (who). Frequency means, not only the number of health events in a population, but the relationship of that number to the size of the population. The resulting proportion or rate allows epidemiologists to compare disease occurrence between different populations.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern refers to the description of health-related events by time, place, and personal characteristics. Time distribution (of a disease): Whether there has been an increase or decrease of the disease over time (years, months, days) ? Time distribution of a disease is the time interval between the appearances of the first case till the appearance of the last one. The peak time is the point of time during which the maximum number of cases occurs.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern Time distribution of a disease may take one of the following forms: Point epidemic: large and excess number of cases over a short period of time (e.g. food poisoning), Secular change: changes occur gradually in disease frequency over long periods of time (years). developed countries have a secular decrease (downward secular change) in morbidities and mortalities from infections BUT they have a secular increase (upward secular change) in other health problems as cancer and heart diseases.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern Time distribution of a disease may take one of the following forms: Point epidemic: Secular change: Seasonal fluctuations: e.g. increase gastroenteritis in infants in summer season and increase bronchitis in winter.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern Place distribution (of a disease): Whether one geographical has a higher frequency of the disease than another? International comparisons (between countries) e.g. malaria. Variations within the same country: e.g. between urban and rural areas. lung cancer increases in urban areas –may be due to air pollution and smoking. Local distribution: within a local community (e.g. a city). rheumatic fever and scabies increase in poorer sectors of a city due to overcrowding and bad housing.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern Personal characteristics: Demographic characteristics: Age,Age, gender,gender, race,race, religion,religion, culture (shared values, assumptions, beliefs, and norms),culture (shared values, assumptions, beliefs, and norms), Biologic characteristics: Blood levels of antibodies, chemicals, and enzymes,Blood levels of antibodies, chemicals, and enzymes,

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Pattern Personal characteristics: Demographic characteristics: Biologic characteristics: Socio-economic factors: social class,social class, income,income, education,education, occupation,occupation, marital statusmarital status Personal habits: smoking,smoking, dietary pattern,dietary pattern, physical exercise,physical exercise, Genetic characteristics: Rh,

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION "Determinants (factors)": Determinants are physical, biological, social, cultural, and behavioral factors that influence health. epidemiologists attempt to search for factors that increase the risk of disease occurrence. epidemiology that is trying to answer the questions of "how" and "why" the health event happened, is referred to as "analytic epidemiology".

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION "Health-related states and events" They include anything that affects the well-being of a population. Early in its history, epidemiology tended to focus on epidemics of communicable diseases. Later, it focused on endemic communicable diseases and noncommunicable diseases. By the middle of the 20th century, focused on chronic diseases, injuries, birth defects, maternal– child health, occupational health, and environmental health. Next, epidemiologists looked at behaviors related to health such as exercise, diet, and seat-belt use. More recently, advances in molecular methods have allowed epidemiologists to examine genetic markers of disease risk. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health related states

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Epidemiology is the study of the distribution and determinants (factors) of health-related states or events in specified populations, and the application of this study to control of health problems. "Specified populations" The clinician is concerned with the health of the individual; BUT the epidemiologist is concerned with the health of the people in a community under study. In other words, the clinician’s patient is the individual; the epidemiologist’s patient is the community.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION "Specified populations" Clinician and epidemiologist have different responsibilities when faced with a person with, say, diarrheal disease. Both are interested in establishing the correct diagnosis. However, clinician usually focuses on treating and caring for the individual, BUT the epidemiologist focuses on: identifying the exposure or source of the agent, the number of other persons who were similarly exposed, the potential for further spread in the community, interventions to prevent additional cases or recurrences.

KEY WORDS IN THE DEFINITIONKEY WORDS IN THE DEFINITION Epidemiology is the study of the distribution and determinants (factors) of health-related states or events in specified populations, and the application of this study to control of health problems. "Application to control" Field epidemiology embodies the application of the collected information to protect and promote the public’s health. Thus, field epidemiology, like the practice of medicine, is both science and art.

Purposes of epidemiology: Identifying causes and/or risk factors for diseases. Determining the extent of the disease in the community, in order to:in order to: establish priorities for research and intervention. Studying natural history (disease stages from start to end) and prognosis of disease (outcome). Evaluating the effectiveness of preventive and therapeutic health programs and services. Conducting surveillance of disease and injury occurrence in populations Investigating outbreaks (e.g., hospital-acquired infections, food-borne infections) to identify their source and install control measures

Characteristics of epidemiology 1.Observational, rather than experimental; 2.Dealing with populations rather than individuals 3.Focusing on free living populations defined by geography, occupation, migration status, health conditions, etc rather than a group of highly-selected individuals studied in a clinic or laboratory;rather than a group of highly-selected individuals studied in a clinic or laboratory; 4.Dealing with health related events, rather than with phenomena not closely related to health status;

Characteristics of epidemiology: 5.Involving measurement and comparison; 6.Take a multidisciplinary approach to understand or solve a problem. statistics,statistics, biology,biology, chemistry, and physics,chemistry, and physics, sociology,sociology, demography,demography, geography,geography, microbiology,microbiology, computer programming,computer programming, administration,administration, toxicology,toxicology, environmental science,..etcenvironmental science,..etc