1. Natural History Of Diseases and Levels of Prevention By : Sourav Goswami Moderator : Dr P R Deshmukh

2. Framework 1.Definition 2.Understanding Natural History of Disease 3.Its Importance 4.Stages 5.Application : Levels of Prevention/Screening/prognosis/E valuation

3. Definition Natural History of a disease signifies the way in which a disease evolves over time from the earliest stage of its prepathogenesis phase to its termination as recovery,disability or death,in the absence of treatment or prevention.

4. Natural history of disease

5. Natural history of Hepatitis B infection SUSCEPTIBLE HOST ON EXPOSURE ENTRY OF HBV DEVEL -OP HEP-B OUTCOME CIRRHOSISCIRRHOSIS CIRRHOSISCIRRHOSIS HCC CARRIER DEATH

6. Natural History of Typhoid Entry of S.typhi Incuba- tion period 14 days P alpabl -e spleen,Rash Headach e, Fever, Pea- soup stool COMPLICATIONS: Hemorrhage Perforation Peritonities COMPLICATIONS: Hemorrhage Perforation Peritonities DEATH/ DISABIL- ITY(carrie -r) DEATH/ DISABIL- ITY(carrie -r) Recovery

7. Susceptible host TIME Incubation period Death Recovery Exposure Onset Latent Infectious Non-infectious Infection No infection Clinical disease

8. Infectious period the time during which the host can infect another susceptible host Non-infectious period the period when the host’s ability to transmit disease to other hosts ceases Incubation period the time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease in question Latent period It is used in non-infectious diseases as the equivalent of incubation period in infectious disease -”Period from disease initiation to disease detection”

9. Stages of Natural History of Disease The natural history of disease can be divided into two stages : 1. Pre-pathogenesis phase 2. Pathogenesis phase

10. 1. Pre-Pathogenesis Phase / Stage of susceptibility In this stage, the disease has not developed but the ground has been laid by the presence of factors that favor its occurrence, for eg : 1.Alcohol consumption for Cirrhosis of liver 2.High Cholesterol, obesity, Type A personality: Heart Disease 3.Smoking, Hypertension, High Cholesterol : Stroke 4.Radiation, Smoking, Immune suppression: Cancer

11. Pathogenesis phase 1. Asymptomatic (Early Pathogenesis) phase 2. Early, Discernible Disease 3. Full-Blown (Classical) Disease 4. Termination - a) Complete Recovery b) Chronic Disease c) Life With Residual Disability d) Death

12. Why is it important to study natural history of disease? 1. For prevention of disease 2.Adjusting lead time & length bias for proper implementation of screening program 2.Forecasting prognosis 3. Evaluation of intervention

13. Prevention

14. Levels of prevention In general, there are mainly three major levels of prevention, depending on the phase of the natural history of the disease : 1. Primary prevention ( also primordial prevention ) 2. Secondary prevention 3. Tertiary prevention

16. Primary prevention seeks to prevent the onset of specific diseases via risk reduction: (a) by altering behaviors /exposures that can lead to disease,(eg : cessation of smoking ) or (b) by enhancing resistance to the effects of exposure to a disease agent (eg : Vaccination ) It can be done by : (1) Health Promotion (2) Specific protection

17. Health Promotion “The process of enabling people to increase control over, and to improve health” (WHO) It is not directed against any particular disease, but is intended to strengthen the host through a variety of approaches : 1.Health education 2.Environmental modifications 3.Nutritional intervention 4.Lifestyle and behavioural changes

18. 1) HEALTH EDUCATION : Most cost effective intervention. Now people have moved to behavior change communication. 2) ENVIRONMENTAL MODIFICATION : # provision of safe water #Installation of sanitary latrines #Control of insects & rodents etc 3)NUTRITIONAL INTERVENTIONS : # Food distribution & nutritional improvements of vulnarable groups ( viz. Mid-day meal in schools,Khichri on Anganwadi etc ) etc 4) LIFE STYLE & BEHAVIOURAL CHANGE : # motivation for healthy lifestyle Contd……

19. Specific protection immunization to protect against specific diseases fortification of foods with specific nutrients (as salt with iodine), use of condoms to protect against STDs, use of chemoprophylactic drugs to protect against particular diseases (as malaria, meningococcal meningitis, etc)

20. # Primordial Prevention This is prevention of the emergence of risk factors in countries or population groups in which they haven't yet appeared. By “individual and mass education” It addresses BROAD HEALTH DETERMINANTS rather than preventing personal exposure to risk factors, which is the goal of primary prevention.

21. Contd …… Thus, outlawing alcohol in certain countries/areas would represent primordial prevention, whereas a campaign against drinking and would be an example of primary prevention.

22. Secondary prevention It include all actions undertaken at the stage of early pathogenesis so as to halt the progress of disease at it’s earliest stage, It is done by “ early diagnosis and prompt treatment” eg : Screening for Cancer/ treatment of Tuberculosis-early diagnosis & prompt treatment/Diagnosis & treatment of malaria

23. Tertiary Prevention It signifies interventions done in the late pathogenesis phase. “All measures available to reduce or limit impairments and disabilities,minimise sufferings caused be existing departures from good health and to promote the patient’s adjustment to irremediable conditions” ( Last,, A Dictionary of Epidemiology ) It can be attained by : a) Disability limitation & b) Rehabilitation

24. Disability limitation (impairment/disability/handicap) Impairment is defined as "any loss or abnormality of psychological, physiological, or anatomical structure or function." Impairment is a deviation from normal organ function; it may be visible or invisible (screening tests generally seek to identify impairments).

25. Disability is defined as "any restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal for a human being." An impairment does not necessarily lead to a disability, for the impairment may be corrected. For example, I am wearing eye glasses, but do not perceive that any disability arises from my impaired vision. A disability refers to the function of the individual (rather than of an organ, as with impairment ).

26. Handicap is defined as "a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual." Handicap considers the person's participation in their social context. For example, if there is a wheel-chair access ramp at work, a disabled person may not be handicapped in coming to work there

27. Disability limitation Concept of disability: DISEASE Accident (1) DISEASE Accident (1) IMPAIRMENT Loss of foot (2) IMPAIRMENT Loss of foot (2) DISABIL- ITY Cannot walk (3) DISABIL- ITY Cannot walk (3) HANDICAP Unemployed (4) HANDICAP Unemployed (4)

28. Contd… Disability limitation includes all measures to prevent the occurrence of further complications, impairments, disabilities and handicaps or even death. For example : When we apply plaster cast to a patient who has suffered Colle’s fracture, we are actually trying to prevent complications and further disability like mal-union or non-union (4)

29. Rehabilitation “Rehabilitation” (Re =restore into, habitat = the original home or environment of the person) “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” It includes Physiotherapy,speech therapy,audiology,psychology, vocational work etc

30. Rehabilitation contd… The following areas of concern have been identified : 1)Medical rehabilitation – restoration of function 2)Vocational rehabilitation- restoration of the capacity to earn a livelihood 3)Social rehabilitation –restoration of family & social relationships 4)Psychological rehabilitation – restoration of personal dignity and confidence

31. Examples of rehabilitation Establishing schools for the blind, provision of aids for the crippled, reconstructive surgery in leprosy, change of profession for a more suitable one etc

32. Knowledge of Natural History of disease helps in adjusting lead-time & length bias…..which helps in implementing proper screening measures

33. HOW SCREENING WORKS P athology Begins Symptom appears DEATH / DISABI LITY DEATH / DISABI LITY SCREENING TEST & EARLY DIAGNOSIS (pre-symptom) X

34. Concept of lead time Possible detection by Screening Pre Detecta- ble Pre Detecta- ble Detectable Pre-Clinical Detectable Pre-Clinical Clinical Disabilit y Death Disabilit y Death AGE 20 30 40 50 60 Clinical detection LEAD TIME

35. Survival time after diagnosis > lead time

37. Length-time Bias Aggressive Disease OnsetClinical Presentation Death Clinical Presentation Death Onset 1 yr sympto Screening interval 1 year 6 mo.asymt period 2 year asym period 4 yr sym Less Aggressive Disease

38. How do we conclude – the screening program is effective? We need to know the natural history of the disease for evaluating the Lead time & Length time bias

39. Prognosis: How much time do I have doc???

40. Prognosis is the prediction of the course of a disease and is expressed as the probability that a particular event will occur in the future

41. Prognosis contd ….. Predictions are based on defined groups of patients and the outcome may be quite different for the individual patients However, knowledge of the likely prognosis is helpful in determining the most useful treatment. Prognostic factors are characteristics associated with outcome in patients with the disease in question. For example, for a patient with AMI, the prognosis is directly related to heart muscle function.

42. Rates commonly used to describe Prognosis RateDefinition 5 year survival Percent of patients surviving 5 years from some point in the course of disease Case fatalityPercent of patients with a disease who die of it Disease-specific mortality Number of people per 10,000 (or 100,000) population dying of specific disease Response Percent of patients showing some evidence of improvement following an intervention Remission Percent of patients entering a phase in which disease is no longer detectable RecurrencePercent of patients who have return of disease after a disease free interval

43. Application of natural history of disease : Evaluation of interventional measures Evaluation helps in 1)Providing feedback on the effectiveness of a program 2)helps to determine whether the program is appropriate for the target population

44. 3) is there any problems with its implementation and support, and 4)whether there are any ongoing concerns that need to be resolved as the programme is implemented. 5)It helps in Comparing intervention modalities

45. Reference 1) AFMC (Association of Faculties of Medicine of Canada) Primer on Population Health-A virtual textbook on Public Health concepts for clinicians 2)Epidemiology by Leon Gordis( Fifth Edition) 3)Park’s testbook of Preventive and social Medicine( 23 rd edition ) 4)Text book of Public Health and community medicine by Armed Force Medical College

46. Thank you !