EPIDEMIOLOGY LATEST.pptx notes on aid of learning

Public health

1. INTRODUCTION TO EPIDEMIOLOGY DR. PENIAS TEMBO (MD) (MPH.MBChB,BSc HB,Dip Med,Cert TM)

2. EPIDEMIOLOGY Objectives At the end of the course, students should be able to demonstrate knowledge of: describe the nature and main uses of epidemiology the epidemiology approach to defining and measuring the occurrence of health related states in population

3. In addition, students are expected to have gained a variety of skills, including ability to: describe the common cause of death, disease and disability in their respective communities outline appropriate study designs to answer specific questions concerning disease causation, natural history prognosis, prevention and evaluation of therapy and other interventions to prevent and control disease

4. WHAT IS EPIDEMIOLOGY Key messages (Things to remember) Epidemiology is a fundamental science of public health Epidemiology has made major contributions to improving population health Epidemiology is essential to the process of identifying and mapping emerging diseases

5. Historical context Origins Epidemiology’s roots are nearly 2500 years old. Epidemiology originates from Hippocrates observations more than 2000 years ago that environmental factors influence the occurrence of disease .              

6. Circa 400 B.C. Hippocrates attempted to explain disease occurrence from a rational rather than a supernatural viewpoint. In his essay entitled “On Airs, Waters, and Places ,” Hippocrates suggested that environmental and host factors such as behaviors might influence the development of disease.

7. 1662 Another early contributor to epidemiology was John Graunt , a London haberdasher and councilman who published a landmark analysis of mortality data in 1662.

8. This publication was the first to quantify patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations.

9. 1800 William Farr built upon Graunt’s work by systematically collecting and analyzing Britain’s mortality statistics . Farr, considered the father of modern vital statistics and surveillance, developed many of the basic practices used today in vital statistics and disease classification

10. He concentrated his efforts on collecting vital statistics, assembling and evaluating those data, and reporting to responsible health authorities and the general public .

11. However, it was not until the 19 th Century that the distribution of disease in specific human population groups was measured to any large extent. This wok not only marked the formal beginnings of epidemiology but also Some of its most spectacular achievements

12. The findings by John snow that the risk of cholera in London was related to the drinking water supplied by a particular company provides a well-known example Snow’s epidemiology studies were one aspect of a wide ranging series of investigations that examined related physical, chemical, biological, sociological and political processes.

13. Comparing rates of disease in subgroups of the human population became common practice in the late C19 th and early C20 th . This approach was initially applied to the control of communicable diseases but proved to be useful way of linking environmental conditions or agents to specific diseases. In the second half of the twentieth century,

14. These methods were applied to chronic non communicable diseases such as heart diseases and cancer, especially in the middle and high-income countries .

15. Recent developments in Epidemiology Epidemiology in modern form is a relatively new discipline and uses quantitative methods to study diseases in human populations, to form prevention and control efforts.e.g. Richard Doll and Andrew Hill studied the relation between tobacco use and lung cancer beginning in the 1950s.

16. In the 1980s, epidemiology was extended to the studies of injuries and violence. In the 1990s, the related fields of molecular and genetic epidemiology (expansion of epidemiology to look at specific pathways, molecules and genes that influence risk of developing disease) took root.

17. Beginning in the 1990s and accelerating after the terrorist attacks of September 11, 2001, epidemiologists have had to consider not only natural transmission of infectious organisms but also deliberate spread through biologic warfare and bioterrorism .

18. Definition of Epidemiology The word “epidemiology “ is derived from Greek words: epi:“ upon ”,demo “ people ” l agos “study”

19. Epidemiology as defined by Last is’ the study of the distribution and determinants of health- related states or events in a specified population, and the application of the study to the prevention and control of health problems.

20. This broad definition of epidemiology can be further elaborated as follows; Study: includes-surveillance, observations, hypothesis testing, analytic research and experiments Distribution: refers to frequency and pattern of occurrence of disease analysis

21. Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population .

22. The resulting rate allows epidemiologists to compare disease occurrence across different populations

23. Pattern refers to the occurrence of health-related events by: time place person.

24. Time patterns may be : Annual seasonal weekly Daily hourly , weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence.

25. Place patterns include: geographic variation , urban/rural differences and location of work sites or schools.

26. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures.

27. Determinants :includes factors that influence health-biological, chemical, physical, socioal, cultural, economic, genetic and behavioural. Health related states and events: refers to –diseases, causes of death,behaviours such as use of tobacco, positive health status, reaction to preventive regimes and provision and use of health services

28. Specified population: include those with identifiable characteristics, such as occupational groups. Application to prevention and control- The aims of public health- to promote, protect and restore health.

29. Concerns of Epidemiology Epidemiologists are concerned not only with deaths, illnesses and disability, but also with more positive health states and most importantly with the means to improve health The term ‘disease ‘encompasses all unfavorable health changes, including injuries and mental health.

30. Uses of epidemiology Assessing the community’s health Making individual decisions Completing the clinical picture Searching for causes- to searching for causal factors that influence one’s risk of disease

31. Epidemiological approach The epidemiological approach to problems of health and disease is based on two major foundation Ask questions and getting answers that lead to further questions Making comparisons and draw inferences

32. Questions related To health events What is the event(problem)? What is the magnitude? Where did it happen? When did it happen? Who are affected? Why did it happen/

33. Questions Related to Health Action What can be done to reduce this problem and it’s consequences? How can it be prevented in the future? What action should be taken by the community ? Who should carry out these activities? Health services, other sectors, where and for whom these activities be carried out?

34. What resources are required? How are these activities be organized? What difficult may arise, and how might they be overcomed?

35. EPIDEMIOLOGY &CLINICAL MEDICINE EPIDEMIOLOGY Population as unit of study Concerned with disease pattern in the entire population Epidemiologists confronted with relevant data derived fro particular epidemiological study-to identify a particular source of infection, mode of spread, CLINICAL MEDICINE Cases/ case with a disease as unity of study Physician is concerned with disease in a individual patients Concerned with both the sick and the healthy Physicians seeks diagnosis from which he derives a prognosis and prescribes specific treatment

36. Epidemiology or an etiological factor in order to determine a future trend and recommend specific control measures Epidemiologist evaluates the outcome of preventive and therapeutic measures instituted which provides the necessary guidance and feed-back to the health care administrator for effective Clinical Medicine Patient comes to a doctor Is based on biomedical concepts with an ever-increasing concern for refining the technique of diagnosis and treatment at individual level

37. Epidemiology Management of public health programmes The investigator goes to the community to find persons who have a disease or experience of the suspected causal factor in question Clinical Medicine The subject matter is easily “perceived “by such techniques as clinical and laboratory examination , postmortem reports

38. Clinical medicine and epidemiology are not antagonistic. Both are closely related, co-existent and mutually helpful Epidemiological enquiries depends on appropriate clinical considerations such as how the disease in question can be identified among individuals comprising the group under scrutiny

39. Likewise, a knowledge of prevalence and prognosis derived from epidemiological research is important to the clinician for the diagnosis and management of individual patients and their families

40. NATURAL HISTORY OF A DISEASE Definition- Natural history of a disease refers to systematic description of the course of disease over time, un affected by treatment.(The course and outcome of disease in individuals and groups)

41. Cont Good Health Subclinical Changes Clinical changes DEATH RECOVERY

42. During the susceptible phase, risk factors are only present or there is accumulation of factors sufficient for the disease process to begin in a susceptible host.

43. During the preclinical or pre symptomatic phase, pathological changes of the disease has started. extending from the time of exposure to onset of disease symptoms, is usually called: The incubation period for infectious diseases the latency period for chronic diseases . There are some physical manifestations, but NO obvious disease is present

44. This period may be as brief as seconds for hypersensitivity and toxic reactions to as long as decades for certain chronic diseases . The onset of symptoms marks the transition from subclinical to clinical disease . In the clinical disease phase, signs and symptoms of diseases are present .

45. In some people, however, the disease process may never progress to clinically apparent illness . In others, the disease process may result in illness that ranges from mild to severe or fatal . This range is called the spectrum of disease . Ultimately , the disease process ends either in recovery, disability or death

46. Chain of infection According to traditional triad model, it holds that infectious diseases result from the interaction of : Agent Host environment

47. T ransmission occurs when the agent leaves its reservoir or host through a portal of exit , is conveyed by some mode of transmission , and enters through an appropriate portal of entry to infect a susceptible host . This sequence is sometimes called the chain of infection.

48. Reservoir The reservoir of an infectious agent is the habitat in which the agent normally lives, grows and multiplies. Reservoirs include: Human –transmission of person to person(mumps, chicken pox) Animals reservoirs (vertebrae animals to human (beings zoonosis -plague) Environment reservoirs( Plants, soil, and water)

49. Portal of exit Portal of exit is the path by which a pathogen leaves its host . The portal of exit usually corresponds to the site where the pathogen is localized. For example: influenza viruses and Mycobacterium tuberculosis exit the respiratory tract schistosomes through urine cholera vibrios in feces

50. Sarcoptes scabiei in scabies skin lesions enterovirus 70, a cause of hemorrhagic conjunctivitis, in conjunctival secretions Some bloodborne agents can exit by crossing the placenta from mother to fetus (rubella, syphilis, toxoplasmosis ), while others exit through cuts or needles in the skin ( hepatitis B) or blood-sucking arthropods (malaria).

51. Mode of transmission: An infectious agent may be transmitted from its natural reservoir to a susceptible host in different ways Direct - direct contact(skin to skin, kissing and sexual intercourse − droplet spread( r efers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking.e.g. Pertussis and meningococcal)

52. Indirect − Air borne through dust or droplet nuclei suspended in the air( measles virus) − Vehicle borne can be contaminated by contaminated food , water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels).

53. − Vectorborne (mechanical or biologic) mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent

54. Port of entry The portal of entry refers to the manner in which a pathogen enters a susceptible host The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act. Often, infectious agents use the same portal to enter a new host that they used to exit the source host.

55. *Knowledge of chain of infection is important as put Interventions that are directed at: -Controlling or eliminating agent at source of transmission - Protecting portals of entry - Increasing host’s defenses

56. Factors which can influence the development of disease are: S train of agent Dose of agent Route of infection Host characteristics Treatment

57. Levels of disease prevention P rimary prevention of a disease These are actions that removes the possibility that a disease will occur. Actions precedes disease or dysfunction(the individuals /population are health) Generalized health promotion and specific protection against diseases The activities are both preventive and promotive

58. Examples of primary prevation Health education about accidents and poisoning prevention,standared of nutrition and growth and development for each stage of life, exercise requirements ,stress management ,protection against occupational hazards,etc Immunizations Risk assessment for disease

59. Family planning services and marriage counseling Environmental sanitation and provision of adequate housing,recreation,and work conditions Removal of any noxious Agents (Toxic agents)in the environment or any agents in the environment that would cause disease-refuse disposal.

60. Preventing agents from being in contact with the host e.g., mosquito nets- to prevent infected mosquitoes.

61. Secondary prevention This is pre clinical / clinical disease stage. It emphasize on early detection/ diagnosis, prompt treatment/ intervention and health maintenance for individuals experiencing health problems. Measures are aimed at people who have a disease. It includes, prevention of progression of a clinical disease( halt),prevention of complications and disabilities.

62. Reduces disease prevalence Level of curative stage to prevent disability( happens in district hospitals )

63. Examples of secondary prevention Screening surveys- DHS-R.P.R Screening tests e.g. early screening and treatment for T.B. to prevent chronocity. Stool for m/c/s to rule out worms. Encouraging medical and dental check ups Teaching self - examination for breast and testicular cancer

64. Tertiary prevention This is the level of disability limitation and rehabilitation . It begins after an illness, when a defect or disability is fixed, stabilized , or irreversible . Usually a point of NO RETURN Its focus is to help rehabilitate individuals and restore them optimum level of functioning within the constraints of disability to try to prevent

65. Hopelessness Helplessness Workelessness Dependence Suicidal tendencies

66. Examples of tertiary prevention Should be helped or request help from clubs Referring a client who has had a colostomy to a support group Use of prosthesis for amputees and also change hobbies e.g. from golfer to dart player Palliative care of terminally ill patients to prevent undignified or painful death Rehabilitation by- Retraining remaining capacities-retrain maximal independence including employment.