Natural History of Diseases & Levels of Prevention.

Professor AB Rajar /IBN-ESINA UNIVERSITY

1. NATURAL HISTORY OF DISEASE & LEVELS OF PREVENTION. AB RAJAR ASSOCAITE PROFESSOR COMMUNITY MEDICINE & HEALTH SCIENCES . MUHAMMAD MEDICAL COLLEGE. MIRPURKHAS

2. Contents Introduction . The definition of natural history of disease. Natural history of disease in man Phases of natural history of disease . Models of disease causation Factors of disease causation Levels of prevention

3. Definition Natural history of disease refers to the progress of a disease process in an individual over time, in the absence of intervention . The process begins with exposure to or accumulation of factors capable of causing disease. Without medical intervention , the process ends with – recovery , – disability, – or death.

4. Natural History of Disease Exposure host Disease Disability Recovery Death

5. Natural History of Disease Knowledge of the natural history of disease ranks alongside causal understanding in importance for disease prevention and control. Natural history of disease is one of the major elements of descriptive epidemiology.

6. Natural History of Disease The natural history of disease is best established by cohort studies . As these studies are costly and laborious, understanding of the natural history of disease is largely based on other epidemiological studies, such as cross-sectional and retrospective studies, undertaken in different population settings.

7. Natural History of Disease What the physician sees in the hospital is just an "episode" in the natural history of disease. The epidemiologist , by studying the natural history of disease in the community setting is in a unique position to fill the gaps in the knowledge about the natural history of disease.

8. Natural History of Disease The natural history and spectrum of disease presents challenges to the clinician and to the public health worker. Because of the clinical spectrum , cases of illness diagnosed by clinicians in the community often represent only the “tip of the iceberg.” Many additional cases may be too early to diagnose or may remain asymptomatic. For the public health worker, the challenge is that persons with undiagnosed infections may nevertheless be able to transmit them to others.

9. PREPATHOGENESIS PATHOGENESIS The process in Man The process in the environment

10. PREPATHOGENESIS PHASE. This refers to the period preliminary to the onset of disease in man . The disease agent has not yet entered man, but the factors which favor its interaction with the human host are already existing in the environment. This situation is frequently referred to as “man in the midst of disease” or “man exposed to the risk of disease”.

11. PATHOGENESIS PHASE. In infectious diseases: This phase begins with entry of the disease “agent” in the susceptible human host. After the entry, agent multiplies and induces tissue and physiological changes, the disease progresses through the period of incubation and later through the period of early and late pathogenesis . The final outcome of the disease may be recovery, disability or death .

12. PATHOGENESIS PHASE. In non-infectious diseases: In chronic diseases , the early pathogenesis phase is less dramatic and is also called as presymptomatic phase . During presymptomatic stage, there is no manifest disease. The pathological changes are essentially below the level of the “clinical horizon ”. The clinical stage begins when recognizable signs or symptoms appear. By the time signs and symptoms appear, the disease phase is already well advanced into the late pathogenesis phase.

13. Preclinical phase Clinical Phase Outcome Cure Control Disability Death (A) ( P) ( S ) ( M) ( D) ( T) Biological onset Pathological changes Signs and symptoms Seek medical care Diagnosis Treatment Natural History of a disease in a patient

14. Natural history of a disease and Levels of prevention • Levels of prevention • Modes of intervention Prepathogenesis Pathogenesis Before man is involved Agent Host Environmental factors Bring agent and ( host together or produce a disease provoking stimulus) Primary prevention • Health promotion • Specific protection The course of disease in man Clinical horizon In the human host Multiplication of agent Tissue or physiological changes Signs and symptoms Illness Disability Defect Chronic state Death Recovery Secondary prevention Early diagnosis and treatment Tertiary prevention • Disability limitation • Rehabilitation Disease Process

15. SPECTRUM OF DISEASE The term “spectrum of disease” is a graphic representation of variations in the manifestations of disease. At the one end of disease spectrum are subclinical infections which are not ordinarily identified, and at the other end are fatal illnesses . In the middle of spectrum lie illnesses ranging in severity from mild to severe . These different manifestations are the result of individuals’ different states of immunity and receptivity .

16. SPECTRUM OF DISEASE

17. ICEBERG PHENOMENON According to this concept, disease in a community may be compared with an iceberg. The floating tip of the iceberg represents what the physician sees in the community, i.e. , clinical cases. The vast submerged portion of iceberg represents the hidden mass of the disease , i.e. , latent, inapparent,presymptomatic and undiagnosed cases and carriers in the community . The waterline represents the demarcation between apparent and in apparent cases.

18. Does not see e.g., Hypertension, Diabetes, Anemia, mental illness etc.

19. ICEBERG CONCEPT OF DISEASE CLINICAL DISEASE SUBCLINICAL DISEASE

20. Models of disease causation

21. Models of disease causation Germ theory of disease Epidemiological Triad BEINGS theory Web of Causation theory Wheel theory

22. Germ Theory of Disease Proposed by Robert Koch and Louis Pasteur. Every human disease is caused by a microbe or germ , which is specific for that disease and one must be able to isolate the microbe from the diseased human being. LOUIS PASTEUR ROBERT KOCH

23. Germ Theory of Disease ROBERT KOCH LOUIS PASTEUR Demonstrated the presence of bacteria in air in 1860. Showed that Anthrax is caused by a bacteria in 1877.

24. Epidemiological Triad

25. Epidemiological Triad

26. Agent Is an element or substance, animate or inanimate , the presence (or absence) of which may initiate or perpetuate a disease process. A disease may have a single agent , a number of independent alternative agents or complex of two or more factors whose combined presence is essential for the development of the disease.

27. Agent characteristics Hepatitis A virus in children has low pathogenicity and low virulence , since many infected children remain asymptomatic and few develop severe illness. In persons with good nutrition and health , measles virus has high pathogenicity but low virulence, since almost all infected persons develop the characteristic rash and illness but few develop the life threatening presentations of measles (pneumonia, encephalitis). In persons with poor nutrition and health, measles is a more virulent disease, with mortality as high as 5-10%. Rabies virus is both highly pathogenic and virulent , since virtually 100% of all infected persons (who do not receive treatment) progress to clinical disease and death.

28. Agent Classification of agents: – Biological – Nutrient – Physical – Chemical – Mechanical – Absence or insufficiency or excess of a factor necessary to health – Social

29. Agent (Cont..) BIOLOGICAL AGENTS : These are living agents of disease,viz: Viruses Bacteria Protozoa Fungi Rickettsia. Metazoa These agents exhibits certain “host related” biological properties such as, infectivity , pathogenicity and virulence.

30. Agent characteristics Infectivity refers to the proportion of exposed persons who become infected. Pathogenicity refers to the proportion of infected persons who develop clinical disease. Virulence refers to the proportion of persons with clinical disease who become severely ill or die.

31. Agent (Cont..) NUTRIENT AGENTS: Protein Fats Carbohydrates. Vitamins. Minerals Water. Any excess or deficiency of intake of nutritive elements may result in nutritional disorders,e.g, Protein energy malnutrition,Anaemia,Goitre,Obesity,vitamin deficiencies.

32. Agent (Cont..) PHYSICAL AGENTS: Exposure to: Excessive heat. Excessive cold. Excessive humidity. Pressure Radiation Electricity Sound These may result in illness.

33. Agent (Cont..) CHEMICAL AGENTS: ENDOGENOUS : Some of the chemicals may be produced in the body as a result of derangement of function,e.g, Urea (Uremia),Serum bilirubin ( jaundice),ketose (ketosis),uric acid (gout),calcium carbonate (kidney stones) etc. EXOGENOUS: Agents arising outside of human host,e.g, A llergens,metals,fumes,dust,gases,insecticides,etc. These may be acquired by inhalation, ingestion or inoculation .

34. MECHANICAL AGENTS: Exposure to chronic friction and other mechanical forces may result in C rushing, T earing, S prains, D islocations A nd even death. Agent (Cont..)

35. Agent (Cont..) ABSENCE OR INSUFFICIENCY OR EXCESS OF A FACTOR NECESSARY TO HEALTH These may be: Chemical factors: hormones (insulin,estrogen,enzymes) Nutrient factors: Lack of structure: Thymus. Lack of part of structure: cardiac defects. Chromosomal factors: turner’s syndrome Immunological factors: agammagloblunaemia.

36. SOCIAL AGENTS: It is also necessary to consider social agents of disease: Poverty. Smoking. Abuse of drugs Alcohol. Unhealthy lifestyles. Social isolation. Maternal deprivation etc. Thus the modern concept of disease “agent" , is a very broad one; it includes both living and non-living agents. Agent (Cont..)

37. HOST FACTORS (Intrinsic) The human host is referred as “soil” and disease agent as “seed”. Demographic characteristics : age,sex,ethinicity. Biological characteristics : genetic factors, blood groups, enzymes, cellular constituents of blood, immunological factors & physiological function of different organ systems of body (BP). Social & economic chacteristics : education,housing,occupation,stress,marital status,socio-economic status etc. Life style factors : personality traits, living habits,nutrition,physical exercise, use of alcohol,drugs,smoking & behavioral patterns.

38. Environment Physical environment – Non living things and physical factors(air, water, soil, housing, heat, light, etc ) Biological environment – Microbial agents, insects, animals, plants and man himself. Psychosocial environment – Lifestyle, poverty, urbanization, community life, income, education, stress etc.

39. Disease Occurrence DIFFERENT DISEASES, IN DIFFERENT COMMUNITIES, SHOW DIFFERENT PATTERNS OF EXPECTED OCCURRENCE : Endemic: habitual presence of a disease within a given geographic area. Hyperendemic :a persistently high level of occurrence. Sporadic : an irregular pattern of occurrence, with occasional cases occurring at irregular intervals.(prevalence is zero)

40. Disease Occurrence Epidemic: occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy and derived from a common or from a propagated source. Public health officials often use the term outbreak , which means the same, because it is less provocative to the public. When an epidemic spreads over several countries or continents, affecting a large number of people, it is called a pandemic (worldwide epidemic).

41. The “BEINGS” Model of Disease Causation This concept postulates that human disease and its consequences are caused by a complex interplay of nine different factors – – Biological factors innate in a human being, – Behavioral factors concerned with individual lifestyles, – Environmental factors as physical, chemical and biological aspects of environment, – Immunological factors, – Nutritional factors, – Genetic factors, – Social factors, – Spiritual factors and – Services factors, related to the various aspects of health care services.

42. The Theory of “Web of Causation” The “epidemiological triad theory” was very effectively used by Leavel and Clark in explaining the natural history of disease and levels of prevention for obviating such departures from the state of health. But it could not explain the causation of non communicable diseases like IHD or road accidents .

43. Web of causation McMahon and Pugh forwarded the theory of “epidemiological web of causation” , wherein the various factors (e.g. hypercholesterolemia, smoking, hypertension) are like an interacting web of a spider. Each factor has its own relative importance in causing the final departure from the state of health, as well as interacts with others, modifying the effect of each other.

44. WEB OF DISEASE CAUSATION

45. WEB OF DISEASE CAUSATION FOR HTN

46. Example of Web of Causation Susceptible Host Infection Tuberculosis Vaccination Genetic Overcrowding Malnutrition Tissue Invasion and Reaction Exposure to Mycobacterium

47. Wheel theory As medical knowledge advanced, an additional aspect of interest that came into play is the comparative role of “genetic” and the “environmental” (i.e. extrinsic factors outside the host) factors in causation of disease. The “triad” as well as the “web” theory does not adequately cover up this differential. To explain such relative contribution of genetic and environmental factors, the “wheel” theory has been postulated.

48. Wheel theory

49. FACTORS OF DISEASE CAUSATION

50. Factors of Disease Causation PREDISPOSING FACTORS : These are factors which create a state of susceptibility , so that the host becomes vulnerable to the agent or to necessary cause, e.g. age, sex, previous illness. ENABLING FACTORS : These are those which assist in the development of (or in recovery from) the disease; e.g. housing conditions, socio-economic status. PRECIPITATING FACTORS : These are those which are associated with immediate exposure to the disease agent or onset of disease, e.g. drinking contaminated water, close contact with a case of pulmonary TB.

51. Factors of Disease Causation REINFORCING FACTORS : These are those which aggravate an already existing disease , e.g. malnutrition, repeated exposures RISK FACTORS : A risk factor is defined as a condition , quality or attribute , the presence of which increases the chances of an individual to have, develop or be adversely affected by a disease process. A risk factor is not necessarily the cause of a disease but does increase the probability that a person exposed to the factor may get the disease.

52. TB Infection(10 - 30 % ) No infection(70 - ) 90 % Active TB(10% ill) - % develop TB within 2 years 5 - % develop TB many years later 5 Latent TB (90% well) - Never develop TB - Not infectious Treated Untreated Cured 50 % die within 5 years 25 % remain sick 25 % recover

53. The Natural history of disease in a patient Preclinical Phase Clinical Phase ( A) (P ) ( S) ( M) ( D) ( T) A ; Biologic onset of disease P ; Pathologic evidence of disease if Sought S ; Signs and symptoms of disease M ; Medical care sought D ; Diagnosis T ; Treatment Gordis L. Epidemiology. WB Saunders Company. 1996

54. LEVELS OF PREVENTION

55. Prevention The goals of medicine are to promote health, to preserve health, to restore health when it is impaired , and to minimize suffering and distress. These goals are embodied in the word "prevention"

56. Prevention; Definition and Concept Actions aimed at eradicating, eliminating or minimizing the impact of disease and disability, or if none of these are feasible, retarding the progress of the disease and disability. The concept of prevention is best defined in the context of levels, traditionally called primary, secondary and tertiary prevention. A fourth level, called primordial prevention, was later added.

57. Determinants of Prevention SUCCESSFUL PREVENTION DEPENDS UPON: a knowledge of causation, dynamics of transmission, identification of risk factors and risk groups, availability of prophylactic or early detection and treatment measures, an organization for applying these measures to appropriate persons or groups, and continuous evaluation of and development of procedures applied

58. Leavell’s Levels of Prevention Stage of disease Level of prevention Type of response Pre-disease Primary Prevention Health promotion and Specific protection Latent Disease Secondary prevention Pre-symptomatic Diagnosis and treatment Symptomatic Disease Tertiary prevention Disability limitation for early symptomatic disease Rehabilitation for late Symptomatic disease

59. LEVELS OF PREVENTION Level of prevention Phase of disease Target Primordial Underlying condition leading to causation Total population and selected groups Primary Specific causal factors Total population, selected groups and healthy individuals Secondary Early stage of disease Patients Tertiary Late stage of disease Patients

60. Levels of prevention Primordial prevention Primary prevention Secondary prevention Tertiary prevention

61. PRIMORDIAL PREVENTION

62. Primordial prevention Primordial prevention consists of actions and measures that inhibit the emergence of risk factors in the form of: Environmental, E conomic , S ocial , B ehavioral conditions and cultural patterns of living etc.

63. Primordial prevention (cont.) It is the prevention of the emergence or development of risk factors in countries or population groups in which they have not yet appeared For example , many adult health problems (e.g., obesity, hypertension) have their early origins in childhood, because this is the time when lifestyles are formed (for example, smoking, eating patterns, physical exercise).

64. Primordial prevention (cont.) In primordial prevention, efforts are directed towards discouraging children from adopting harmful lifestyles The main intervention in primordial prevention is through individual and mass education

65. Primordial prevention (cont.) EXAMPLES: National policies and programes on nutrition involving the agricultural sector, the food industry, and the food import export sector Comprehensive policies to discourage smoking Programes to promote regular physical activity Making major changes in lifestyle

66. PRIMARY PREVENTION

67. Primary prevention Primary prevention can be defined as the action taken prior to the onset of disease, which removes the possibility that the disease will ever occur. It signifies intervention in the pre-pathogenesis phase of a disease or health problem. Primary prevention may be accomplished by measures of: “ Health promotion ” and “ S pecific protection ”

68. Primary Prevention

69. Primary prevention (cont.) It includes the concept of " positive health ", a concept that encourages achievement and maintenance of "an acceptable level of health that will enable every individual to lead a socially and economically productive life". Primary prevention may be accomplished by measures designed to promote general health and well-being, and quality of life of people or by specific protective measures .

70. Approaches for Primary Prevention: The WHO has recommended the following approaches for the primary prevention of chronic diseases where the risk factors are established: – a. Population (mass) strategy – b. High -risk strategy

71. Population (mass) strategy: “Population strategy" is directed at the whole population irrespective of individual risk levels. For example, studies have shown that even a small reduction in the average blood pressure or serum cholesterol of a population would produce a large reduction in the incidence of cardiovascular disease The population approach is directed towards socio-economic, behavioral and lifestyle changes

72. High -risk strategy: The high -risk strategy aims to bring preventive care to individuals at special risk. This requires detection of individuals at high risk by the optimum use of clinical methods.

73. SECONDARY PREVENTION

74. Secondary prevention: It is defined as “ action which halts the progress of a disease at its incipient stage and prevents complications.” The specific interventions are: E arly diagnosis: ( e.g. screening tests, breast self examination, pap smear test, radiographic examinations, case finding programme, etc.) A nd adequate treatment:

75. Secondary prevention (Cont..) Secondary prevention attempts to arrest the disease process, restore health by seeking out unrecognized disease and treating it before irreversible pathological changes take place, and reverse communicability of infectious diseases. It thus protects others from in the community from acquiring the infection and thus provide at once secondary prevention for the infected ones and primary prevention for their potential contacts.

76. Early diagnosis and treatment WHO Expert Committee in 1973 defined early detection of health disorders as “ the detection of disturbances of homoeostatic and compensatory mechanism while biochemical, morphological and functional changes are still reversible.” The earlier the disease is diagnosed, and treated the better it is for prognosis of the case and in the prevention of the occurrence of other secondary cases.

77. SECONDARY PREVENTION

78. Tertiary prevention It is used when the disease process has advanced beyond its early stages. It is defined as “all the measures available to reduce or limit impairments and disabilities, and to promote the patients’ adjustment to irremediable conditions.” Intervention that should be accomplished in the stage of tertiary prevention are disability limitation , and rehabilitation.

79. Disability limitation disease impairment disability handicap

80. TERTIARY PREVENTION IMPAIRMENT DISABILITY HANDICAP Any loss or abnormality of psychological, physiological or anatomical structure or function The inability to carry out certain activities because of impairment, that are considered normal for his age and sex. The inability to discharge the obligations required of him and play the role expected of him in the society. Loss of foot Cannot walk unemployed

81. Rehabilitation Rehabilitation is “ the combined and coordinated use of medical, social, educational, and vocational measures for training and retraining the individual to the highest possible level of functional ability.”

82. TYPES OF REHABILITATION. Rehabilitation Medical rehabilitation Vocational rehabilitation Social rehabilitation Psychological rehabilitation

83. Strategy for Prevention Assess Exposure Identify Populations at High Disease Risk based on demography / ( family history, host factors..) Conduct Research on Mechanisms ( including the study of genetic susceptibility) Apply Population - Based Intervention Programs Evaluate Intervention Programs Modify Existing Intervention Programs

84. CONCLUSION “ What the physician sees in the hospital is just an “ episode” in the natural history of disease. The epidemiologist, by studying the natural history of disease in the community setting, is in a unique position to fill the gaps in our knowledge.”

85. THANK YOU FOR SUCH ATTETION