Introduction To Epidemiology PDF

INTRODUCTION TO EPIDEMIOLOGY Prepared by: Monica Joyce S. Sespeñe CS-BPS FACULTY  LEARNING CONTENT A. HISTORY OF EPIDEMIOLOGY B. BASIC CONCEPTS & PRINCIPLES OF EPIDEMIOLOGY a. Etiology and Natural History of Diseases b. Chain of infection c. Functions of...

INTRODUCTION TO EPIDEMIOLOGY Prepared by: Monica Joyce S. Sespeñe CS-BPS FACULTY  LEARNING CONTENT A. HISTORY OF EPIDEMIOLOGY B. BASIC CONCEPTS & PRINCIPLES OF EPIDEMIOLOGY a. Etiology and Natural History of Diseases b. Chain of infection c. Functions of Epidemiology d. Uses of Epidemiologic information e. Epidemiologic approach f. Contributions of Epidemiologists  LEARNING OUTCOMES ✓ LO1 Trace the historical events of Epidemiology in the current health events. ✓ LO2 Identify the patterns of disease and injury in human populations through Epidemiologic triad and Chain of infection models. ✓ LO3 Apply the principles and functions of Epidemiology to common diseases that affects public health.  EPIDEMIOLOGY EPIDEMIOLOGY refers to the study of the distribution and determinants of health-related states or events in specified populations. This study applies to the control of health problems from epidemic to pandemic. Also defined as the basic science of public health. 1 SCOPE OF EPIDEMIOLOGY The target of Epidemiology is the level of human population emphasizing the positive health states for improvement of population’s health. Epidemiologist defines population in geographical area such as country, city or town, subgrouping is done with respect by sex, age group, ethnicity and other patterns. The structure of populations vary between geographical areas and time periods. Epidemiology as concern with public health has several targets: 1. Causation 2. Natural History or Etiology of Disease 3. Description of health status of populations 4. Evaluation of intervention Epidemiology has several categories but the most focused and distinguished types are Classical and Clinical Epidemiology. 1. Classical Epidemiology - 2. Clinical Epidemiology - study population-oriented, studies origins patients in health care settings rather of health problems in community, than in the community at large. Their infectious agents; nutrition; the goal is to improve the prevention, early environment; human behavior; and detection, diagnosis, treatment, the psychological, social, economic, prognosis, and care of illness in and spiritual state of a population. individual patients who are at risk for, Focused on discovering risk factors or already affected by, specific diseases. that might be altered in a population 3 to prevent or delay disease, injury, and death. 3 HISTORICAL DEVELOPMENT IN EPIDEMIOLOGY 1. HIPPOCRATES- a Greek physician who is known as the Father of medicine and the first Epidemiologist. ❖ Hippocrates marked the idea of epidemiologic observation on how diseases affected populations and how diseases are spread. Addressed the relation of time and seasons, place, environmental conditions and disease control to issues of diseases. His ideas of epidemiologic observation are still applied in epidemiologic concepts ❖ Introduced the concept of Endemic and Epidemic. o Endemic is an indigenous characteristic of a specific population or environment. Diseases affects a particular small population. Source: https://www.geni.com/people/Hippocrate o Epidemic is disease that strike a large number or people in a specific population or community.  2. IGNAZ SEMMELWEIS- a physician-epidemiologist who discovered and introduced the benefits of Hand washing. ❖ He observed from his investigation that diseases were spread from patient to patient by unclean hands. ❖ He also discovered that any infected and putrefied tissue whether from living patients or cadaver could cause a disease. ❖ Stated that hand washing using chlorinated limes between each examination reduced illness and death from childbed fever. ❖ His discovery is one of the easiest disease-and infection-control methods known. Source: www.Britannica.com Source: www.cdc.gov  JOHN GRAUNT (1662)- a London haberdasher and councilman. ❖ He published a landmark analysis of mortality data in 1662 which became the first method to quantify patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations JOHN GRAUNT (1662) Source: https://prabook.com/web/john.graunt WHO Mortality rate of Covid-19 in line graph Source: https://www.thelancet.com/journals/laninf/article  JOHN SNOW (1854) - an English physician and anesthesiologist. ❖ Most important contributor in the field of Epidemiology, referred by many other epidemiologist as “Father of Epidemiology”. ❖ Studied the epidemiology of Cholera, and by that he introduced descriptive and analytic approaches ❖ He identified various methods of transmission (waterborne disease) and incubation times as well as the cause-effect association. JOHN SNOW Source: Historic development in Epidemiology Chapter 2 BASIC CONCEPTS AND PRINCIPLES OF EPIDEMIOLOGY The following are the key terms that explains some important principles of epidemiology: ❖ STUDY- it uses scientific, systematic and data-driven methods. ❖ DISTRIBUTION- as it deals with frequency and patterns of diseases. ❖ Frequency- refers to number of health events in relation to the size of population. ❖ Patterns- refers to the occurrence of health-related events by time, place, and person. ❖ DETERMINANT- it is use to find causes and other factors that influences that occurrence of disease and other health-related events. ❖ HEALTH-RELATED STATES- Addresses both communicable and non-communicable diseases. ❖ SPECIFIED POPULATIONS- concerned with the collective health of the people in a community or population. ❖ APPLICATION- applied gained knowledge to public health. 1 A. ETIOLOGY AND NATURAL HISTORY OF DISEASES Public health and medical practitioners tend to know the cause of diseases to determine how and when to intervene. In Epidemiology, the goal of therapeutic or preventive intervention is to alter the natural history of a disease in a favorable way. 1. MECHANISM and CAUSE OF DISEASE. In epidemiology, etiology of disease is significant in the process of investigation, Epidemiologists distinguish biological mechanisms and social, behavioral and environmental causes of disease. EXAMPLE: OSTEOMALACIA Figure 1 shows the defect on bones caused by Osteomalacia, a disease causing weakness of the bone, often through a deficiency of vitamin D. In this case, the social, nutritional, and environmental causes set in motion the biochemical and other biologic mechanisms of osteomalacia, which may ultimately lead to maternal and infant mortality. Figure 1.1: Osteomalacia (Source: Dreamstime,com) A. ETIOLOGY AND NATURAL HISTORY OF DISEASE 2. CAUSATION. Epidemiology also functions as Determinants, it’s used to identify the factors that influence the occurrence of disease. Disease causation introduced many models but Epidemiologic Triad (figure 1.2) shows the simplest which is also known as the traditional model for infectious disease. What is this Epidemiologic Triad? This is a model which explains how diseases are spread by the interaction between the host and the agent within the environment as a support of transmission of the agent to the host. Figure 1.2 Epidemiological triad (Source: Microbio notes) Epidemiologic Triad is composed of three corners/ vertices, the Agent, the susceptible Host, and the Environment. ETIOLOGY AND NATURAL HISTORY OF DISEASE- Causation EPIDEMIOLOGIC TRIAD CORNERS/VERTICES: a. AGENTS are the microbes and other components causing disease. There are three categories: ❖ Biologic Agents- allergens, bacteria, virus, biologic toxins and foods. ❖ Chemical Agents- chemical toxins, dust ❖ Physical Agents- bullet wounds, blunt trauma, crash injuries, radiation, heat, cold and noise. However, not all agents cannot directly cause disease, it needs a variety of factors such as exposure to organisms Figure 1.3 Infectious agents Source: mayoclinic.org to cause a disease. ETIOLOGY AND NATURAL HISTORY OF DISEASE- Causation b. HOST A factor that is responsible for the degree to which the individual is able to adapt to the stressors produced by the agent. Basically, the person, animal or any organism Figure 1.4: Sick person who is vulnerable to developing infectious agent. Some people become susceptible when Immune system is low, Poor physical resistance and etc., ❖ Chances of exposure to the agents are influenced by the host behavior such as sexual practices, hygiene and Figure 1.6: sick old man other personal choices, sometimes it depends on the Figure 1.5: new born baby age and sex. Fig. 1.4 source. www. ❖ Host resistance is influenced by a person’s genotype, cdc.gov nutritional status and body mass index, immune system, Fig. 1.5 source: and social behavior. www.gograph.com Fig.1.6 source: https:raisingchildren.net Figure 1.7: sick animal (dog) Fig.1.7. source: www.pawsphilippines.we ebly.com ETIOLOGY AND NATURAL HISTORY OF DISEASE- Causation c. ENVIRONMENT The extrinsic factors which influences the probability and circumstances of contact between the host and the agent. ❖ Environmental factors include: (1) poor sanitation in the living environment, rapid reproduction of infectious agents could possibly Figure 1.8: Squatter area Copyright: Robin Hammond / Panos happen and as well as the rapid distribution of the (www.scidev.net) infection. (2) Crowded places can rapidly spread infectious diseases, geology and climate. ❖ Both biological and socio-economic factors affect the spread of disease. Figure 1.9: Situation inside MRT Philippines Source: jazzyhappy.com ETIOLOGY AND NATURAL HISTORY OF DISEASE- Causation d. VECTOR It is considered as an environmental factor which transmits infectious diseases, these are microorganisms, mammals, insects and other organisms which are capable of carrying and transmitting disease. ❖ In epidemiology, Vectors includes human groups and other Figure 1.10 Vector born pathogens Source: www.nature.com inanimate objects such as needles or syringes, surgical equipment used in laboratories are factors that may spread disease. Figure 1.11 Used syringe Source: www.personneltoday.com Figure 1.12 Surgical Equipmeny Source: www.shutterstock.com  Figure 1.7: Malaria Epidemiological triad This Epidemiologic triad illustrates the Image source: bettercare pattern of disease including vector. Let’s have an example: Human Malaria disease: ❖ AGENT: Plasmodium vivax - a parasite that causes Malaria. ❖ VECTOR: Female Anopheles mosquito ❖ HOST: Human ❖ ENVIRONMENT These insects have a high level of sensitivity to temperature and humidity in their surroundings. The activity and number of anopheline mosquitoes, as well as the transmission of malaria, are governed by rainfall, altitude, and temperature (Baird, J.K. et al. 2002). B. CHAIN OF INFECTION Infectious diseases result from the interaction between the agent, host and environment. A chain of reaction explains the sequence of transmission of diseases. Chain of infection is composed of the six main links of infection: 1. Infectious Agents 2. Reservoir/Host 3. Portal of Exit 4. Mode of Transmission 5. Portal of Entry 6. Susceptible Host Figure 2: Chain of infection Source: mms.mckesson.com Chain of Infection Six (6) Main Links to Infections 1. Infectious Agent Infectious agents are the microorganisms carrying diseases. Examples: Bacteria, Viruses, Parasites, Fungi and etc. 2. Reservoir –refers to the habitat of the infectious agent where they normally live, grow and reproduce. There are three types of Reservoir: Human, Animal and environment. a. Human reservoirs are the common target of infectious agents. Diseases are spread through contact from person to person. b. Animal Reservoir spreads disease through interaction between two animals, humans can also be an incidental/accidental host when that person had direct contact with infected animal. c. Environmental reservoir refers to plant, soil and water where fungal agents live and multiply. Figure 3: Reservoir Source: emedia.rmit.edu.au Chain of Infection Six (6) Main Links to Infections 3. Portal of Exit- the path by which pathogen time to leave the host. The portal of exit usually corresponds to the site where the pathogen is localized. Example: Amoebiasis through feces, influenza viruses and Mycobacterium tuberculosis exit the respiratory tract. Figure 4: Portal of Exit Source: slideserve.com Chain of Infection Six (6) Main Links to Infections 4. Mode of transmission- infectious agents could be transmitted from natural reservoirs to a susceptible host. There are different modes of transmission, these are Direct and Indirect. a. Direct transmission- in this mode, infectious agents are transmitted from reservoir to susceptible host directly through either direct contact or droplet spread. ❖ Direct contact refers to skin-to-skin contact, kissing and sexual intercourse or possibly direct contact with contaminated soil or vegetation. Example: Syphilis are transmitted through personal contact. Hookworm is transmitted through direct contact with Figure 5: Direct contact example Source: source: news-medical.net contaminated soil ❖ Droplet spread refers to liquid droplets from an infected person through sneezing, coughing or talking. Transmission occurs when an infected person releases droplets over a few feet from the susceptible host. Example: Meningococcal infection is transmitted by droplet spread from infectious patient to susceptible host. Figure 5: Droplet Spread (Sneezing) Source:healthline.com Chain of Infection Six (6) Main Links to Infections b. Indirect transmission- in this mode, infectious agents are transmitted from a reservoir to a host through air particles, inanimate objects such as vehicles and inanimate intermediaries (vectors). ❖ Airborne transmission infectious agents are carried by dust or droplet nuclei that are suspended in air. Airborne dust includes particles that are suspended on the surface and become re-suspended by air currents. Droplet nuclei remain suspended in the air for a long period of time and possibly blown from distance. Droplet nuclei are dried residue of less than 5 microns in size. Example: Measles, when a patient infected with measles went to a clinic for check-up, the next patient who will enter the clinic room may possibly catch the infection because measles virus remains suspended in the air. ❖ Vehicles refers to foods, water, biologic products (blood), fomites, beddings and surgical equipment. The vehicle may become an environment of the infectious agent where they can grow, multiply and produce toxins. ❖ Vectors refers to insects that may carry the infectious agents through mechanical and biological means. Example of Mechanical transmission is house fly, landed on feces of dog and then on foods which is eaten by a human, the infectious agent travels from the feces to food. Biological transmission refers to infectious agents which undergo maturation in an intermediate host before it can be transmitted to humans just like malaria worm disease. Chain of Infection Six (6) Main Links to Infections 5. Portal of Entry- the sites where infectious agents or pathogens enter a susceptible host. Portals of entry must provide the environment that allow them to multiply. ❖ Portal of entries are skin, mucous membrane, blood, eyes and etc., some of the infectious agents enter the same portal to enter a new susceptible host, the portal they used to exit the source host and some follow the “fecal-oral” route. Examples: Mycobacterium tuberculosis exits the respiratory tract of the source host then enters the respiratory tract of the new host. Fecal-oral route example is Amoebiasis, Entamoeba histolytica exits the host source in feces, these infectious agents will be carried by contaminated water or food and now enters the mouth of the new host by drinking the contaminated water. Figure 8: Portal of Entry Source: slideserve.com Chain of Infection Six (6) Main Links to Infections 6. Susceptible Host- the final link in the chain of infection. Susceptibility of the host varies on genetic or constitutional factors, specific immunity or nonspecific factor, these factors could resist infection or limit infection. Susceptibility Factors: a. Genetic make-up either decreases or increases susceptibility. b. Specific immunity refers to protective antibodies that fight against specific agents. Antibodies are developed in the process of Vaccine, toxoids, or trans-placental transfer (mother to fetus) or by injection of antitoxin or immune globulin c. Non-specific factors that can be the source of defense from infections are skin, cough reflex, gastric acidity and other nonspecific immune response. d. Other factors are malnutrition, alcoholism, inborn diseases and therapy and etc. To clearly understand the Chain of infection, observe this Illustration (Figure 2.1). Examples are presented in every link of Infection.  LEARNING CHECK 2.2 ACTIVITY 2: Draw the map or chain of infection of CHICKEN POX and identify the infectious agent, reservoir, portal of entry, the mode of transmission (direct or indirect), the portal of exit and the susceptible host. D. EPIDEMIOLOGIC FUNCTIONS 1. PUBLIC HEALTH SURVEILLANCE is the ongoing, systematic collection, analysis, interpretation, and dissemination of health data to help guide public health decision making and action2. Monitoring the community pulse to illustrate the ongoing pattern of disease occurrence to reach an effective and effective result of investigation, prevention and control. 2 Example: Morbidity and mortality reports- a surveillance data for local and health departments. Figure 2.2 illustrates the cycle of surveillance, starting Figure 2.2 SURVEILLANCE CYCLE (Source: cdc.org) from Public and health care providers (laboratories, hospitals, clinics and other medical-related providers) then there will be a submission of surveillance report (e.g. Mortality and Morbidity report) to the health departments. Health departments will then give feedback from the reports, and these feedbacks will be reported back to the Public and health providers. EPIDEMIOLOGIC FUNCTIONS 2. FIELD INVESTIGATION surveillance provides information for action. Field investigation requires coordination from a large team to characterize the extent of the pandemic and to identify its cause. ❖ Generally, the objective of an investigation may simply be to learn more about the natural history, clinical spectrum, descriptive epidemiology, and risk factors of the disease before determining what disease intervention methods might be appropriate. Field investigation of Covid-19 Philippines Source: World Health Organization EPIDEMIOLOGIC FUNCTIONS 3. ANALYTIC STUDIES help in the process of surveillance and investigation by evaluating the credibility of the hypotheses. To achieve an effective analytic study, epidemiologists follow the steps from formulation of study design, conducting the research data, analysis of data and interpretation (study-findings, recommendations etc.,) Source: www.manuscriptedit.com EPIDEMIOLOGIC FUNCTIONS 4. EVALUATION is the process of determining the relevance, effectiveness, efficiency, and impact of activities to established goals systematically and objectively. Evaluation could be formative (Plan 6. POLICY DEVELOPMENT the application of the operations) or summative (outcomes/product). study to the control of health problems. Providing input, recommendations and reports regarding disease control strategies, reportable disease 5. LINKAGES maintains the relationship with each regulation and health-care policy improves the staff who are in the team of field investigation. This policy on the public health. is to promote current and future collaboration. Mechanisms for sustaining such linkages include official memoranda of understanding, sharing of published or on-line information for public health audiences and outside partners, and informal networking that takes place at professional meetings. C. USES OF EPIDEMIOLOGICAL INFORMATION 1.Community Health Assessment- COMMUNITY NEEDS Epidemiologic information are used as a ASSESSEMENTS STEPS factual framework for decision by the Public health officials who are responsible in policy development, implementation, and evaluation. The purpose is to assess the health of the populations or community to improve what is lacking on the current health status of the community. This approach is under epidemiologic research called Descriptive epidemiology Source: Centers for Disease Control and which requires identification and analysis of Prevention. Community Health Assessment relevant data source such as by person, aNd Group Evaluation (CHANGE) Action Guide place, and time. C. USES OF EPIDEMIOLOGICAL INFORMATION 2. Making individual decisions- the epidemiologic findings may influence the public, consciously or unconsciously, in their daily decisions affecting their health. The early epidemiologic risk assessment affected the choices of people daily. It’s either being healthy or taking the risk and get sick. Source: Penn Medicine Source: Notes From Poland C. C. USES OF EPIDEMIOLOGICAL INFORMATION 3. Completing the clinical pictures (Solving the mystery)- Epidemiologists rely on health- HEALTH DEPARTMENT care providers and laboratorians to establish (PHYSICIANS, LABORATORY DEPT.) the proper diagnosis of individual patients when conducting disease outbreak investigation. However, Epidemiologists also contributes to physicians’ understanding of the clinical picture and natural history of disease. EPIDEMIOLOGY INFORMATION Example: epidemiologists, clinicians, and researchers around the world have collaborated to characterize SARS. FINAL DECISION: TYPE OF DISEASE & ITS CAUSES C. C. USES OF EPIDEMIOLOGICAL INFORMATION 4. Searching for causes- Epidemiological researches mostly focuses in searching for causal factors that influence one’s risk of EPIDEMIOLOGY disease. It is to identify a cause to develop appropriate public health action. However, much of epidemiology is based on ecological reasoning. Despite that, epidemiology often provides sufficient information to support HEALTH effective action. Their collaboration with DEPARTMENT laboratory science provide the evidence needed to establish causation. Example: The epidemiologist identifies variety of risk factors during an outbreak of pneumonia. FINAL DECISION: DISEASE CAUSATION D. EPIDEMIOLOGIC APPROACH The practice of epidemiology relies on a systematic approach, epidemiologist work can be classified in three simple terms: 1. Counts cases or health events, and describes them in terms of time, place, and person; 2. Divides the number of cases by an appropriate denominator to calculate rates; 3. Compare these rates over time or for different groups of people. These terms are used in investigating an outbreak of disease, remember these terms as we reach chapter 4 and discuss the details of Outbreak Investigation E. CONTRIBUTIONS OF EPIDEMIOLOGISTS 1. Investigating epidemics and new disease 2. Studying the Biological Spectrum of Disease 3. Surveillance of Community Health Interventions 4. Setting Disease Control Priorities 5. Improving Diagnosis, Treatment and Prognosis of Clinical disease 6. Improving Health Services Research 7. Providing expert testimony in courts of law -END OF LECTURE- References BOOK REFERENCES 1. Merrill, R. M. (2016). Introduction to Epidemiology (7th ed.). Jones & Bartlett Learning. 2. Dicker, R., Coronado, F., Koo, D., & Parrish, R. G. (2021). Principles of Epidemiology in Public Health Practice, 3rd Edition (3rd ed.). CDC (Centers for Disease Control and Prevention). 3. Jekel’s Epidemiology, Biostatistics, Preventive Medicine, and Public Health. (2020). Elsevier. 4. Baird, J.K, et al., (2002). Epidemiologic Measures of Risk of Malaria. Public Health Resources. pg 385. https://core.ac.uk/download/pdf/188100131.pdf ONLINE REFERENCES 1. Chain of infection. (2021). Ottawa Public Health. https://www.ottawapublichealth.ca/en/professionals-and-partners/chain-of- infection.aspx 2. Rise in Japan’s COVID-19 Cases Starting to Speed Up. (2020, May 30). Nippon.Com. https://www.nippon.com/en/japan-data/h00691/rise-in- japan%E2%80%99s-covid-19-cases-starting-to-speed-up.html