CONCEPT OF DISEASE

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CONCEPT OF DISEASE

  1. 1. CONCEPT OF DISEASE• A condition of the body or some part or organ of the body in which its functions are deranged.• It is a mal-adjustment of human organism to the environment.• I t is deviation from normal function.
  2. 2. CONCEPT OF CAUSATION• DEMONISTIC THEORY• DEVILISITIC THEORY• TRIDOSHAS THEORY• FOUR HUMOURS THEORY• YANG and YIN Principles• GERM THEORY - Louis Pasteur, Robert Koch• EPIDEMIOLOGICAL TRIAD• MULTI FACTORIAL THORY – Web of disease causation, Wheel of causation
  3. 3. Henle-Koch’s Postulates1. The agent should be present in every case of the disease under appropriate condition2. The agent should not be present in any other disease as a fortuitous and Non- Pathogenic agent3. The agent must be isolated from the body of the individual in pure culture4. It should induce disease in a new susceptible experiment animal
  4. 4. NATURAL HISTORY OF DISEASE• IT IS 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
  5. 5. NATURAL HISTORY OF DISEASE• PRE-PATHOGENIC PHASE OR SUSCEPTIBILITY STAGE• PATHOGENIC PHASE1. INCUPATION PERIOD2. PRODROMAL STAGE3. STAGE OF OVERT DISEASE4. STAGE OF DEFERVESCENCE5. STAGE OF CONVALESCENCE
  6. 6. FACTORS AFFECTING THEGRADIENT OF INFECTION • Infectivity • Pathogenicity • Virulence • Antigenicity
  7. 7. TYPE OF INFECTION• Latent infection• Sub-clinical infection or inapparent or occult• Atypical infection• Severe clinical infection
  8. 8. Factors for development or spread of infectious disease• An etiological agent responsible for the disease should be present• There should be a reservoir or carrier for the etiological agent to survive• The infecting agent should be able to escape from the reservoir of infection through the portal of exit• There should be a possible source of entry to transmit the agent to a new susceptible host• The agent should be able to invade the new host• The host should be susceptible
  9. 9. Background• Infectious disease epidemiology – the occurrence of infectious disease in a given host is dependent on the presence of disease in other members of the population and the length of time that infected hosts are able to transmit disease to others – understanding these characteristics of a disease allow us to develop rational measures to control disease
  10. 10. Definition & Stages • Definition ; The course of a disease from onset (inception) to resolution. • Stages Progress to a fatal termination Stage of Pre-symptomatic Clinically pathologic Remission and relapses stage manifest disease onset Regress spontaneously, leading to recoveryRisk Factors Precursors Effect of Treatment Prognostic factor
  11. 11. Risk factor• Risk factor; An aspect of personal behavior or life style, an environmental exposure, or an inborn or inherited characteristic, that, in the basis of epidemiologic evidence, is known to be associated with health-related condition (s) considered important to prevent. – Risk marker; increased probability of a specified outcome; not necessarily a causal factor – Determinant; can be modified by intervention, thereby reducing the probability of occurrence of disease or other specified outcomes
  12. 12. 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
  13. 13. THE NATURAL HISTORY OF A DISEASESTIMULUS to HOST REACTION RECOVERY the HOSTinterrelation ofAgent, Host and Latent Period (Pre- Symptoms, with or without Defects,Environmental symptomatic) Signs(Clinical) Disability factorsPREPATHOGE PERIOD OF PATHOGENESIS NESIS Health Promotion Disability Limitation Specific Early Diagnosis and Prompt Protection Treatment, Rehabilitation PRIMARY SECONDARY TREATMENT TERTIARY PREVENTIONPREVENTION PREVENTION (Leavells Level of Application of Preventive Medicine)
  14. 14. TIME Death Infection Clinical disease Susceptible host Recovery No infection Incubation period Latent Infectious Non-infectiousExposure Onset
  15. 15. • Latent period the time interval from infection to development of infectiousness• Infectious period the time during which time 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 infection to development of clinical disease
  16. 16. • e.g : Chicken pox – an infectious disease caused by the varicella- zoster virus – the latent period for chicken pox is shorter than the incubation period, so a child with chicken pox becomes infectious to others before developing symptoms
  17. 17. TIME Death Infection Clinical disease Susceptible host Recovery No infection Incubation period Latent Infectious Non-infectiousExposure Onset
  18. 18. • Other examples? – HIV (AIDS) • latent period relatively short • infectious period occurs (many years) before the onset of symptoms
  19. 19. TIME Death Infection Clinical disease Susceptible host Recovery No infection Incubation period Latent InfectiousExposure Onset
  20. 20. e.g : Malaria – caused by protozoan parasites of the genus Plasmodium – the stages of the parasite that are infective to mosquitoes occur about 10 days after the development of symptoms – latent period is around 10 days longer than the incubation period, so early treatment of symptoms could have an important effect on transmission
  21. 21. Natural history of disease TIME Death Infection Clinical disease Susceptible host Recovery No infection Incubation period Latent InfectiousExposure Onset
  22. 22. Latent Period of Chronic Disease• Definition; "Interval between exposure to a disease- causing agent and the appearance of manifestations of the disease"• cf. incubation period in infectious disease 1) brief exposure Two conditions 2) prolonged or continuous exposure
  23. 23. Primary Prevention• Preventing the occurrence of disease or injury by modifying risk factors.• Various aspects are considered to produce effective primary prevention program. Especially, advancing knowledge of disease causation must be required.‘
  24. 24. Primary Prevention• ** Guidelines for effective prevention programs(RB Wallace, GD Everett,1986) – Programs must be based on scientific evidence. – Prevention programs should be supported by effective data system. – Programs should be flexible. – Programs must be sensitive to ethical issues. – Programs should be targeted to the recipients most in need. – Programs should muster a variety of community resources. – Effective prevention requires legislative action and social policy decisions. – Programs should be continuous.
  25. 25. Primary Prevention• General health promotion – Proper nutrition, mental hygiene, adequate housing, and appropriate balance between work and play, est and exercise, and useful and productive place in society, are among the best recognized factors ontributing to maintenance of optimum health.(Commission on Chronic illness, USA, 1957)‘• Specific protection• Health Promotion – Health promotion is any combination of educational, organizational, economic, and environmental supports for behavior and conditions of living conducive to health (LW Green, 1992).
  26. 26. Criteria for the Development of Health Promotion and Education Programs• A health promotion program should address one or more risk factors which are carefully defined, measurable, modifiable, and prevalent among the members of a chosen group, factors which constitute a threat to the health status and the quality of life of target group members.• A health promotion program should reflect a consideration of the special characteristics, needs, and preferences of its target groups(s) From APHA Technical Report
  27. 27. Criteria for the Development of Health Promotion and Education Programs• health promotion programs should include interventions which will clearly and effectively reduce a targeted risk factor and are appropriate for a particular setting• A health promotion program should identify and implement interventions which make optimum use of available resources.• From the outset, a health promotion program should be organized, planned, and implemented in such a way that its operation and effects can be evaluated.
  28. 28. MODES OF TRANSMISSION• DIRECT • INDIRECT TRANSMISSION TRANSMISSION• DIRECT CONTACT • VECHICLE BORNE • VECTOR BORNE• DROPLET INFECTION • A) mechanical• CONTACT WITH SOIL • B) biological• INOCULATION INTO • AIR-BORNE SKINOR MUCOSA • FOMITE BORNE• TRANSPLACENTAL • UNCLEAN HANDS AND FINGERS
  29. 29. BIOLOGICAL TRANSMISSION• Propagative• Cyclo-Propagative• Cyclo-developmental• Transovarial transmission• Trans-stadial transmission
  30. 30. SOURCE OF INFECTION• It is defined as the person, animal, object or substance from which an infectious agent passes or is disseminated to the host
  31. 31. RESERVOIR• It is defined as “any person, animal, arthropod, plant, soil, or substance “(or combination of these in which an infectious agent lives and multiplies, on which it depends primarily for survival, and where it reproduces itself in such manner that it can be transmitted to a susceptible host”
  32. 32. CARRIERSA Carrier is defined as an infectedperson or animal that harbours aspecific infectious agent in theabsence of discernible clinicaldisease and serves as a potentialsource of infection for others
  33. 33. CARRIERS• TYPE • PORTAL OF EXITA) Incubatory A) UrinaryB) Convalescent B) IntestinalC) Healthy C) Respiratory• DURATIONA)TemporaryB)Chronic
  34. 34. FEATURES OF CARRIER1. Presence of specific microbes in the body2. Absence of apparent symptoms and signs3. Shedding of micro-organisms in the discharges or excretions4. As a source of infection to others
  35. 35. INCUPATION PERIODTHE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUSAGENT AND APPEARANCE OFTHE FIRST SIGN OR SYMPTOMOF THE DISEASE IN QUESTION
  36. 36. FACTORS AFFECTING THE INCUPATION PERIOD• DOSE OF INOCULUM• SITE OF MULTIFICATION• RATE OF MULTIFICATION• HOST DEFENCE MECHANISM
  37. 37. FACTORS TO DETERMINE THE INCUBATION PERIOD • GENERATION TIME • INFECTIVE DOSE • PORTAL OF ENTRY • INDIVIDUAL SUCEPTIBILITY
  38. 38. IMPORTANCE OF INCUPATION PERIOD• Tracing the source of infection and contact• Period of surveillance• Immunization• Identification of point source or propagated epidemics• Prognosis
  39. 39. MEDIAN INCUPATION PERIOD• IT IS DEFINED AS THE TIME REQUIRED FOR 50% OF THE CASES TO OCCUR FOLLOWING EXPOSURE
  40. 40. LATENT PERIODIT HAS BEEN DEFINEDAS THE PERIOD FROMDISEASE INITIATION TO DISEASE DETECTION
  41. 41. GENERATION TIMEIT IS DEFINED AS THE INTERVAL OFTIME BETWEEN RECEIPT OFINFECTION BY A HOST AND MAXIMALINFECTIVITY OF THAT HOST
  42. 42. SERIAL INTERVALTHE GAP IN TIMEBETWEEN THE ONSET OFTHE PRIMARY CASE ANDTHE SECONDARY CASE
  43. 43. COMMUNICABLE PERIODIt is defined as the time duringwhich an infectious agent may betransferred directly or indirectlyfrom an infected person to anotherperson, from an infected animal toman , or from an infected person toan animal, including arthropods
  44. 44. SECONDARY ATTACK RATEIt is defined as the number ofexposed persons developing thedisease within the range of theincubation period, followingexposure to the primary case
  45. 45. Number of exposed persons developing the SAR= disease within the range of the incubation period  100 Total number of exposed /susceptible
  46. 46. HERD IMMUNITY• IT IS THE LEVEL OF RESISTENCE OF A COMMUNITY OR GROUP OF PEOPLE TO A PARTICULAR DISEASE
  47. 47. BEHAVIOUR OF DISEASE IN THE COMMUNITY 1. EXOTIC 2. SPORADIC 3. ENDEMIC 4. EPIDEMIC 5. PANDEMIC 6. OUTBREAK
  48. 48. EPIDEMICIt is the unusual occurrence in acommunity or region of cases of anillness, specific health-relatedbehavior, or other health relatedevents clearly in excess of normalexpectancy (LAST,1995)
  49. 49. OUT BREAKTWO OR MORE RELATEDCASES IN INFECTIONS,SUGGESTING THEPOSSIBILITY OF A COMMONSOURCE OR TRANSMISSIONBETWEEN CASES
  50. 50. FACTORS IN DISEASE CAUSATION1. Predisposing factors age, sex and previous illness2. Enabling factors low income, poor nutrition, bad housing, inadequate medical care3. Precipitating factors exposure to a specific disease agent or noxious agent4. Reinforcing factors repeated exposure, unduly hard work
  51. 51. THE EPIDEMIOLOGIC TRIANGLE "triad" that play a role in disease process Agent Vector Host EnvironmentTRADITIONAL MODEL OF INFECTIOUS DISEASE CAUSATION
  52. 52. AGENTAs an element or substance, animate or inanimate,the presence (or absence) of it may initiate or perpetuate a disease process
  53. 53. HOSTA person or other living animal, that affords subsistence or lodgment to aninfectious agentunder natural conditionHost factorsIntrinsic factors that influence an individual’s exposure, susceptibility, orresponse to a causative agent
  54. 54. ENVIRONMENTAs the aggregate of all the external conditionsand influence affecting the life and development of an organismEnvironmental factorExtrinsic factors which affect the agent and the opportunity forexposure
  55. 55. AGENTa. Nutritional agent carbohydrate, vitamin, fat, protein, mineral, water Example : - diabetes mellitus, obesitas, hyperlipidemia, kwashiorkor - avitaminosis - cretinism, anemia - edema, dehydration
  56. 56. b. Chemical agent polutan , drugs, Hg, Pb, Ag, arsenicum, pesticide (Chlorinated Hydrocarbon CCl4 : DDT, endrin, dieldrin and organo hosphate, diacynon, malathion, butazinon), cosmetics, etc.c. Physical agent collision, traffic accident, falling down, dust, climate (frost bite, heat stroke)
  57. 57. d. Infectious agent - Virus : dengue, morbili, varicella, hepatitis - Ricketsia : typhus exanthematicus, Rocky MountainSpotted Fever, scrub typhus (rat-bite fever) - Bacteria : gram (+), gram (-) ; bacil, coccus, acid fast resistence, anaerob, etc. - Fungi : tinea capitis, tinea cruris, tinea pedis - Protozoa : plasmodium, amoeba - Metazoa : worm (ascaris , ancylostoma, etc.)
  58. 58. HOSTIntrinsic factors that play a role in disease process- age- sex- religion- customs- occupation- marital status- family background- genetic-hereditary- ethnic / race- physiologic / psychological status- habit / behavior- immune status- previous disease
  59. 59. ENVIRONMENT1. Physical environment geographic, geology, climate2. Biological environment people, flora, fauna, food population density3. Socioeconomic income, education, culture, urbanization, economic growth, poverty, fertility, etc.
  60. 60. NATURAL HISTORY AND SPECTRUM OF DISEASE
  61. 61. Natural history of disease The progress of a disease process in an individual overtime in the absence of intervention recoveryExposure host disease disability death
  62. 62. INCUBATION PERIODThe time interval between contact with an agent and the first clinical evidenceof resulting diseaseDepends on :• Portal of entry (defense mechanism)• The ability of multiplication (infectivity)• Number of agents• Level of antibody in the hostIt varies individually
  63. 63. Type of incubation period in disease outbreaknumber ofcases A B time A : skewed to the left the disease has a short incubation period B : skewed to the right the disease has a longer incubation period
  64. 64. DEFENCE MECHANISMTHE ABILITY TO REACT AGAINST AGENT INVASION IN THE BODYConsist of :• The external defense mechanism : physical andchemical reaction• The internal defense mechanism : cellular and humoral immunity
  65. 65. EXTERNAL BARRIERRespiratory tract sense of smell, cough andsneeze reflex, mucous membrane, hair of the nose, ciliated epithelium.Small particles < 5 can enter directly into the alveoli.Digestive tract sense of taste, vomit reflex, gastricacid fluid, peristaltic of intestine and diarrheaSkinstructure of the skin, sebaceous glands, apocrine and accrine sweat glands,hairEyeblink reflex, eye brow, eye lash, tears
  66. 66. If the external barrier can not eliminate the agentinternal defense mechanism will continue the defence mechanism process by: - Inflammation - Isolation by fibrocyte - Macrophage phagocytosis - Antibody reactionImmunization a way to increase the internal defence mechanism
  67. 67. The natural history and spectrum of disease challenges to the clinician and to the public health workerTo the clinicianBecause of cases diagnosed by clinicians in the community often represent only the “tipof the iceberg”, it is important to do the “case finding” and report it to the publichealth workerTo the public health workerWhile searching the rest of the cases, they should prevent disease transmission andoutbreak
  68. 68. ICEBERG PHENOMENE CLINIC CLINICAL HORIZON SUB CLINIC CUREThe proportion of sub clinical patients are greater in number than thepatients with complete symptomsThis portion should be early detected, because it has the capability oftransmitting the disease causing outbreak
  69. 69. CELL RESPONSE HOST RESPONSE Lysis of cell Death of organism Clinical disease Inclusion body formationDiscernable effect Classical and severe disease or cell transformation or Moderate severity cell dysfunction mild illness Viral multiplication Infection without without visible clinical illness change or (asymptomatic infection) Subclinical disease incomplete viralBelow visual change maturation Exposure without Exposure without attachment and/or infection cell entry
  70. 70. CHAIN OF INFECTION
  71. 71. AGENT CHARACTERISTIC1. Natural characteristics of the agent The morphology, physiology, reproduction, motility, metabolism, need of oxygen , temperature, production of toxin, antigen, living cycle, reaction against physical and chemical substance2. Characteristic of the agent related to infection in human a. infectivity b. pathogenicity c. virulence d. antigenicity e. tropism
  72. 72. 3. Reservoir of agent4. Portal of entry and portal of exit5. The incubation period6. The spread of the disease7. Natural cycle of infection
  73. 73. INFECTIVITYThe ability of agent to attack, adapt, live and multiplicate in the hostPATHOGENICITYThe ability of agent to produce a local or general reaction in the hostVIRULENCEThe ability to elicit a severe clinical manifestation
  74. 74. ANTIGENICITYThe agent’s ability to stimulate host production of antibody such as agglutinin,opsonin, precipitin, antitoxin, lysine, complement fixating substance,etc.Disease with high antigenicity can be prevented by immunizationExample :• Typhoid fever, morbili : highly antigenic• Tuberculosis : doubtful• Influenza virus has lots of strain : rather difficult to develop an effective vaccine
  75. 75. Agent with high infectivity and pathogenicity but low antigenicity will cause arelatively high disease prevalence in the communityAgent with high infectivity but low pathogenicity usually produce a mild or sub clinicalsymptom and carrierTROPISMThe agent preference to attack and stay in special location in the host• Cholera : digestive tract• Staphylococcus : mostly in the skin• Herpes zoster : nerve system• Poliomyelitis : anterior-horn cells of spinal cord
  76. 76. HERD IMMUNITYThe immunity of a group of people / community.The resistance of a group to invasion and spreading of an infectious agentbased on the resistance to infection of a high proportion of individual members of thegroup.The herd immunity reduces the susceptibility to infection or can resist a communicabledisease epidemic.The higher herd immunity the higher the power to defence of an epidemicoccurrence.
  77. 77. The high incidence of communicable disease can be due to : the high proportion of the susceptible individual or the low portion of herd immunity in the populationThe practical aspect of the concept of herd immunity : the necessity ofimmunization program for the whole population to prevent the occurrence of anepidemic
  78. 78. RESERVOIRHabitat in which an infectious agent normally lives, grows and multiplies 1. HUMAN RESERVOIR 2. ANIMAL RESERVOIR 3. ENVIRONMENTAL RESERVOIR
  79. 79. 1. Human reservoir - Persons with symptomatic illness - CarrierCarrier : a person without apparent disease who is nonetheless capable of transmitting the agent to othersa. Asymptomatic carrier (never show symptoms during the time they are infected)b. Incubatory / convalescent carrier (who are capable of transmission before or after they are clinically ill)c. Chronic carrier (who continues to harbor an agent)
  80. 80. 2. Animal reservoirInfectious disease that are transmissible under normal conditions from animals to humanare called zoonoses• Dog, cat, ape : rabies• Rat : rat bite fever, plaque, leptospirosis• Cattle : sheep, goat, camel, cow, pig (anthrax, brucellosis, bovine tuberculosis, tularemia, ring worm)• Arthropode : flies, cockroach, mosquito
  81. 81. 3. Environmental reservoir (soil) • Clostridia (tetanus, botulism, welchii) • Fungi • Bacteria (dust particle : mycobacterium tuberculosis) • Parasite (helminthiasis)
  82. 82. PORTAL OF ENTRY AND PORTAL OF EXITThe path by which an agent enters of leaves the source host.Usually corresponds to the site at which the agent is localized.It is necessary to understand about it because it related to how the disease beingtransmitted in other way we can assume how the prevention of the disease.
  83. 83. Portal of entry- digestive tract- respiratory tract- skin- genital- eye- blood vessel systemThe portal exit seem to be the same with the portal entry, sometimes some diseasehave other way of exit beside the former way.Hepatitis infectiosa, typhus abdominalis :beside come out by fecal also can be detected in urine and blood.
  84. 84. TRANSMISSION4 transmission ways :1. Contact transmission a. Direct transmission : by mucous contact e.g. genital-genital, oral-genital, oral-oral b. Indirect : hand-mouth, droplet transmission
  85. 85. 2. Vehicle transmission - Transmission by common vehicle : food, fluid, milk, blood, serum, vaccine - The agent can be transmitted by ingestion, injection or inoculation3. Vector transmission The arthropods have a role in this transmission4. Air borne - droplet nuclei - dust
  86. 86. Transmission of Dengue Virus by Aedes aegypti Mosquito feeds / Mosquito refeeds / acquires virus transmits virus Extrinsic Intrinsic incubation incubation period period Viremia Viremia0 5 8 12 16 20 24 28 DAYS Illness Illness Human #1 Human #2
  87. 87. Replication and transmission of Dengue virus (part 1)1. Virus transmitted 1 to human in mosquito saliva 22. Virus replicates in target organs 43. Virus infects white 3 blood cells and lymphatic tissues4. Virus released and circulates in blood
  88. 88. Replication and transmission of Dengue virus (part 2)5. Second mosquito 6 ingests virus with blood6. Virus replicates in mosquito midgut and other organs, 7 infects salivary glands 57. Virus replicates in salivary glands
  89. 89. Theoretically, the spreading of the disease can be stopped by cutting off every stepof the disease phase.The principle of communicable disease control is to cut off the chain of transmissionof the disease.Example : 1. To cut the connection between the reservoir andthe host (contact person) by : • individual hygiene • environmental sanitation 2. To increase the defense mechanism by : • immunization • nutrition 3. In case the colonization has been occurred : • early diagnosis & prompt treatment • screening : malaria, STD, HIV-AIDS
  90. 90. IMPLICATIONFOR PUBLIC HEALTHBy knowing how an agent exits and enters a host, and what its modes oftransmission are, we can determine appropriate control measures, includingprevention methodsFOR CLINICAL/HOSPITAL SETTINGPatients may be treated and/or isolated with appropriate“precautions”
  91. 91. NATURAL HISTORY OF ANY DISEASEPREPATHOGENIC PATHOGENIC D E A T H CLINICAL 1 2 3 Agent Host Environment Clinical Horizon interaction Sub Clinic Convalescence Cured + Sequel PRIMARY SECONDARYPREV TERTIARY PREVENTION I ENTION II PREVENTION III
  92. 92. STAGE OF PREVENTIONI. PRIMARY PREVENTION “Health promotion and specific protection” A. Health Promotion 1. Health education 2. Nutrition 3. Development 4. Housing 5. Marriage counseling 6. Genetic 7. Periodic physical examination
  93. 93. B. Specific protection 1. Immunization 2. Personal hygiene 3. Environmental sanitation 4. Occupational hazard 5. Protection to accident 6. Specific nutrition 7. Protection to carcinogen 8. Avoidance of allergic material
  94. 94. II. SECONDARY PREVENTION “Early diagnosis and prompt treatment” 1. Case finding 2. Screening survey 3. Selective examination a. Cure and prevent b. Preventing the spread c. Preventing complication and sequel d. Shorten of disability
  95. 95. Natural history of disease Onset of Usual time of symptoms diagnosis Exposure Pathologic changes Stage of Stage of Stage of Stage of susceptibility subclinical clinical recovery, disease disease disability or deathPRIMARYPREVENTION SECONDARY PREVENTION TERTIARY PREVENTION
  96. 96. The natural history of diseaseSTAGE 1: SusceptibilityDESCRIPTION: Risk factors which assist the development of disease exist, but disease has not developedEXAMPLE: Smoking
  97. 97. The natural history of disease (cont’d)STAGE 2: Presymptomatic diseaseDESCRIPTION: Changes have occurred to lead toward illness but disease is not yet clinically detectableEXAMPLE: Alveoli deteriorate
  98. 98. The natural history of disease (cont’d)STAGE 3: Clinical DiseaseDESCRIPTION: Detectable signs and/or symptoms of disease existEXAMPLE: Emphysema detected by pulmonary function test
  99. 99. The natural history of disease (cont’d)STAGE 4: DisabilityDESCRIPTION: Disease has progressed to the point of causing a residual effectEXAMPLE: Person has difficulty breathing
  100. 100. LEVELS OF PREVENTIONLEVEL: PrimaryDESCRIPTION: Promote general health and avoid risk factors for disease --- Utilize protective measures to prevent susceptibility and presymptomatic diseaseEXAMPLE: Stop smoking or choose not to start; avoid areas where people are smoking
  101. 101. LEVELS OF PREVENTION (cont’d)LEVEL: SecondaryDESCRIPTION: Early detection and timely treatmentEXAMPLE: Routine pulmonary function tests for those at risk; medicine to help patients breath more easily; smoking cessation programs if patient smokes
  102. 102. LEVELS OF PREVENTION (cont’d)LEVEL: TertiaryDESCRIPTION: Rehabilitation and prevention of further disease or disabilityEXAMPLE: Oxygen therapy; facilitating ambulation with technical devices
  103. 103. PREVENTION APPROACHESPopulation-Based Approach:• Preventive measure widely applied to an entire population (public health approach)• Strive for small absolute change among many persons• Must be relatively inexpensive and non-invasive
  104. 104. PREVENTION APPROACHESHigh-Risk Approach:• Target group of individual at high risk• Strive for strong risk factor control• Often times requires clinical action to identify the high risk group and to motivate risk factor control.
  105. 105. LEVELS OF PREVENTION (Review)PRIMARY PREVENTION Prevention of disease by controlling risk factors (e.g., non-smoking promotion)
  106. 106. LEVELS OF PREVENTION (Review) SECONDARY PREVENTIONReduction in consequences of disease by early diagnosis and treatment (e.g., cervical cancer screening)

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