1. 1. PRESENTED BY:Kinza FatimaAnam ArshadIfra ZulfiqarAmna Mohammad AfzalSidrah Yousaf ChaudarySamra Zanjabeel
2. 2. Epidemiology(Study of epidemics)
3. 3. Epidemiology derives fromThe word epidemiology derives fromGREEK wordEpi ( Upon)Demons(people)Ology(science)So it deals with what fall among people.
4. 4. DEFINITIONS:A Modern Definition.According to WHOStudy of the occurrence anddistribution of health-related diseasesor events in specified populations,including the study of the determinantsinfluencing such states, and theapplication of this knowledge tocontrol the health problem
5. 5. Other Definitions:Science of community medicine that dealswith study of distribution, determents andfrequency of disease in population is knownas Epidemiology OLDER DEFINITION:The study of the occurrence of illness.
6. 6. HistoryThe Greek physician Hippocrates is sometimessaid to be the father of epidemiology. He is the firstperson known to have examined the relationshipsbetween the occurrence of disease andenvironmental influences. He coined the termsendemic (for diseases usually found in someplaces but not in others) and epidemic (for diseasethat are seen at some times but not others).One of the earliest theories on the origin of diseasewas that it was primarily the fault of human luxury.This was expressed by philosophers such asPlato & Rousseau, and social critics likeJonathan Swift
7. 7. HistoryIn the medieval Islamic world, physiciansdiscovered the contagious nature of infectiousdisease. In particular, the Persian physicianAvicenna, considered a "father of modernmedicine," in The Canon of Medicine (1020s),discovered the contagious nature of tuberculosisand sexually transmitted disease, and thedistribution of disease through water and soil.He also used the method of risk factor analysis,and proposed the idea of a syndrome in thediagnosis of specific diseases.
8. 8. HistoryWhen the Black Death (bubonic plague) reached AlAndalus in the 14th century, Ibn Khatimahypothesized that infectious diseases are caused bysmall "minute bodies" which enter the human body andcause disease.Another 14th century Andalusian-Arabian physician,Ibn al-Khatib (13131374), wrote a treatise called Onthe Plague, in which he stated how infectious diseasecan be transmitted through bodily contact and "throughgarments, vessels and earrings."
9. 9. HistoryJohn Graunt, a professional haberdasherand serious amateur scientist, publishedNatural and Political Observations ... uponthe Bills of Mortality in 1662. In it, he usedanalysis of the mortality rolls in Londonbefore the Great Plague to present one ofthe first life tables and report time trends formany diseases, new and old.He provided statistical evidence for manytheories on disease, and also refuted manywidespread ideas on them.
10. 10. HistoryHe used chlorine in an attempt to clean thewater and had the handle removed, thusending the outbreak. (It has beenquestioned as to whether the epidemic wasalready in decline when Snow took action.)This has been perceived as a major eventin the history of public health and can beregarded as the founding event of thescience of epidemiology.
11. 11. HistoryIn the middle of the 16th century, a famous Italiandoctor from Verona named Girolamo Fracastorowas the first to propose a theory that these verysmall, unseeable, particles that cause disease werealive.They were considered to be able to spread by air,multiply by themselves and to be destroyable by fire.In this way he refuted Galen's theory of miasms(poison gas in sick people).In 1543 he wrote a book De contagione etcontagiosis morbis, in which he was the first topromote personal and environmental hygiene toprevent disease.
12. 12. HistoryThe miasmatic theory of disease held that diseasessuch as cholera or the Black Death were caused by amiasma (Greek language: "pollution"), a noxious formof "bad air". In general, this concept has beensupplanted by the more scientifically founded germtheory of disease.
13. 13. History Other pioneers include Danish physician P. A.Schleisner, who in 1849 related his work on theprevention of the epidemic of tetanus neonatorum onthe Vestmanna Islands in Iceland.Another important pioneer was Hungarian physicianIgnaz Semmelweis, who in 1847 brought down infantmortality at a Vienna hospital by instituting adisinfection procedure.His findings were published in 1850, but his workwas ill received by his colleagues, whodiscontinued the procedure. Disinfection did notbecome widely practiced until British surgeonJoseph Lister 'discovered' antiseptics in 1865 inlight of the work of Louis Pasteur
14. 14. HistoryIn the early 20th century, mathematical methods wereintroduced into epidemiology by Ronald Ross,Anderson Gray McKendrick and others.
15. 15. The Unique Contribution ofEpidemiologyEpidemiologic studies are conducted inhuman populationsLab and animal researches are incapable ofpredicting the applicability of findings from aparticular species of animals to humansEpidemiologic research providedinformation for public health decisions longbefore the basic mechanism of a particulardisease
16. 16. EPIDEMIOLOGICAL DISEASESAlphabetical OrderAnaplasmosisBabesiosisChickenpox (Shingles or Varicella)Corona virusDiphtheriaEhrlichiosisGiardiasis
17. 17. Haemophilius InfluenzaeHemolytic Uremic Syndrome (HUS)Hepatitis AHepatitis BHepatitis C
18. 18. InfluenzaMeaslesMumpsNorovirusPertussis (Whooping Cough)Q FeverRabiesRubella (German Measles
19. 19. SalmonellosisShingles (Varicella or Chickenpox)Strep pneumoniaeTetanus (Lockjaw)TuberculosisVaricella (Chickenpox and Shingles)Vector borne DiseaseVibrio parahaemolyticus
20. 20. Common epidemic diseases inPakistan and mode oftransmission: food or waterborne diseases: bacterialdiarrhea, hepatitis A and E, and typhoidfevervectorborne diseases: dengue fever andmalariaanimal contact disease: rabies
21. 21. TERMINOLOGIESEndemic When aninfectiousdisease more orless prevailing ona locality orcommunity calledas endemic E.g.. ChickenpoxPandemic When anepidemic spreadfrom one countryto another oreven whole worldinfecting most ofthe populationthen theconditions calledas pandemic E.g.. Swine fluEpidemic Sudden outbreak ofinfectiousdisease thatspreads rapidlythroughpopulationaffecting a largenumber ofpopulation inshort period oftime is called asepidemic E.g.. AIDS inAfrica
22. 22. CONTINUE.. DISEASE:A pattern of response by a living organism to someform of invasion by a foreign substance or injurywhich causes an alteration of the organismsnormal functioning also an abnormal state in which the body is not capableof responding to or carrying on its normally requiredfunctions PATHOGENS:organisms or substances such as bacteria, viruses,or parasites that are capable of producing diseases PATHOGENISES:the development, production, or process ofgenerating a disease
23. 23. CONTINUE PATHOGENIC:means disease causing or producing PATHOGENICITY:describes the potential ability and strength of apathogenic substance to cause disease INFECTIVE:diseases are those which the pathogen or agenthas the capability to enter, survive, and multiply inthe host
24. 24. CONTINUEVIRULENCE:the extent of pathogenicity or strength of differentorganisms the ability of the pathogen to grow, thrive, and todevelop all factor into virulence the capacity and strength of the disease toproduce severe and fatal cases of illnessINVASSIVNESS:the ability to get into a susceptible host and cause adisease within the host The capacity of a microorganism enter into andgrow in or upon tissues of a host
25. 25. CONTINUEETIOLOGY:The factors contributing to the source of orcausation of a diseaseTOXINS:A poisonous substance that is a specific product ofthe metabolic activities of a living organism and isusually very unstable notably toxic when introduced into the tissues,and typically capable of inducing antibodyformation
26. 26. CONTINUEHYPERENDEMIC:Diseases that affect a high proportion of population atrisk.HOLOENDEMIC:Disease that is highly prevalent in a population & iscommonly acquired early in life in most all of thechildren of the populationMESOENDEMIC:Diseases that affect a moderate proportion ofpopulation at risk.
27. 27. HYPOENDEMIC:Diseases that affect a small proportion of populationat risk.SPORADIC:A Disease that is normally absent from a populationbut which can occur in that population, & althoughrelay & without predictable regularity.INCIDENCE:the extent that people, within a population who donot have a disease, develop the disease during aspecific time period.
28. 28. CONTINUEPREVALENCE:The number of people within a population who havea certain disease at a given point in timePOINT PREVALENCE:How many cases of a disease exist in a group ofpeople at that moment.ANTIBIOTICS:Substance produced by or a semisyntheticsubstance derived from a microorganism &able indilute solution to inhibit or kill anothermicroorganism
29. 29. CONTINUEAGENT: is the cause of the disease Can be bacteria, virus, parasite, fungus, mold Chemicals (solvents), Radiation, heat, natural toxins(snake or spider venom)HOST:is an organism, usually human or animal, thatharbors the diseasePATHOGEN:disease-causing microorganism or relatedsubstanceENVIRONMENT:is the favorable surroundings and conditions external tothe human or animal that cause or allow the disease orallow disease transmission
30. 30. CONTINUEVECTOR:Any living non-human carrier of disease thattransports and serves the process of diseasetransmission Insects: fly, flea, mosquito; rodents; deerRESERVOIRS:humans, animals, plants, soils or inanimate organicmatter (feces or food) in which infectiousorganisms live and multiply Humans often serve as reservoir and hostZOONOSIS:When a animal transmits a disease to a human
31. 31. CONTINUEINFECTION:The entry & development or multiplication of diseaseproducing agent in or on body of man/animal iscalled infection.INCUBATION PERIOD:Time interval b/w the entry of diseased agent into thebody of host appearances of first sign & symptomsof disease.
32. 32. CONTINUEINFECTIOUS AGENT:Any agent which is capable of producing aninfection is called infectious agent.INFESTATION:An infestation is the presence of animalparasite either externally or internally.CONTACT:Any person who has remain in association
33. 33. CONTINUEwith the infected person or the infectedparticles can also develop the disease.CONTAMINATION:It is the presence of infectious agent in orupon the surface of articles, wound orinanimate object such as cloth, toys, bed,floor etc.CONTAGIOUS DISEASE:A disease which is transmitted by contact.
34. 34. CONTINUECOMMUNICABLE DISEASE:the disease which is transmitted from oneperson to another directly or indirectlythrough infectious agent like Food, Air,Water, Dust is called communicabledisease.NON COMMUNICABLE DISEASE:The diseases which are not transfer toanother but they occur within the patienthimself e.g. cancer, diabetes, hypertension
35. 35. CONTINUEFOMITES:Inanimate articles other than food& water ,contaminated by infectious discharge fromthe patient& are capable of transmitting theinfectious agent to the healthy person e.gcloth, towel, handerkerchief.CARRIER:one that spreads or harbors an infectiousorganism
36. 36. CONTINUELATENT PERIOD:The time from first contact with nonliving agentuntil symptoms appear (cold, heat, irradiation,poisons, toxins, etc.).EPIZOOTIC:An condition of outbreak of disease in animalsPOLLUTION:The existence of certain abnormal amounts oftoxic chemicals or dust within anenvironmental category such as air, water,food, or soil
37. 37. CONTINUECLINICAL INFECTION:The state in which the host has symptoms,feels ill, or dies. Clinical infection anddisease are terms often used as synonyms.
38. 38. Components Of EpidemiologyDiseasefrequencyDistribution ofdiseaseDeterminants ofdisease
39. 39. Continue The components of epidemiologyinclude the following:Disease determinants - which are thecause or factors, the Distribution, andmorbidity or mortality. Distributionrefers to how the disease occurs in thepopulation, Morbidity refers tosickness, and Mortality refers todeath
40. 40. 1. DISEASE FREQUENCYRate & Ratio, analysis of the incidence& the prevalence of a disease. Thereare two main measures of diseasefrequencyA) PREVALENCEB) INCIDENCEQuantification of the existence oroccurrence of disease
41. 41. INCIDENCEThe probability that healthy people willdevelop a disease during a specified periodof time (that is, the number of new cases ofa disease in a population over a period oftime). Incidence measures the rapidity withwhich a disease occurs or the frequency ofaddition of new cases of a disease. Thesenew cases of disease occur either throughonset of the disease in current
42. 42. Members of the population or byimmigration into the population ofpersons already ill. The formula fordetermining incidence rates is:Incidence rate = No. of new cases during a given period 10n Population at riskduring the same period PREVALENCE:The number of people in a populationwho have a given disease at a givenperiod of time.The formula for determining prevalencerates is:
43. 43. Prevalence =All new & preexisting cases during a given time period 10nPopulation at risk during the same time periodNote: It is important to remember that therates for both incidence and prevalenceinclude a factor of 10 such as per 100 orper 1,000. (Rate is usually expressed per1,000.) The value of n depends on therelative frequency of a given disease
44. 44. 2.DISTRIBUTION OFDISEASEWho is getting the disease within apopulationWhere and when the disease isoccurringTo describe patterns of disease aswell as to formulate hypothesesconcerning causal or preventivefactors
45. 45. Continue..PERSON TIME PLACEAge PointepidemicGeographicRace cyclical Longitude&latitudeSex Secular GeologicOccupation ClimaticEducation GeoPoliticalHobbies Urban/RuralIndustryPollution
46. 46. 3. DETERMINANTS OFDISEASEBy this we mean the cause of a disease. Itincludes :PRIMARY DETERMINENTSPrimary cause of disease.SECONDARY DETERMINENTSFactors responsible for the spread of thedisease.
47. 47. Epidemiological triadHOSTAGENTVECTORENVIRONMENT
48. 48. Disease CycleIntervention:The interaction of host, agent, andenvironment makes up the diseasecycle. Although the agent must bepresent for a disease to occur, it aloneis not a sufficient cause. The cyclemust be completed for the disease tooccur or conversely, the cycle must bebroken to control the disease.
49. 49. FACTORS RESPONSIBLE FORTHE SPREAD OF DISEASEAgentSpecific living or inanimate objects that can causehealth problems to hosts.Environmentis the favorable surroundings and conditions externalto the human or animal that cause or allow thedisease or allow disease transmissionHostGroups of living organisms (people, animals, andplants) that, under certain circumstances, maybecome unhealthy.
50. 50. AGENTIt includes bilogical agents Physical agents Nutritional agents Chemical agents Mechanical agentsBIOLOGICAL AGENTInvolves in occurrence of disease1) Virus(HIV)e.g AIDS2) Rickettsia(typhus)3) Fungi(candida)e.g vaginal itching4) Bacteria(streptococcus)e.g pneumonia5) Protoza(plasmodium)e.g malaria
51. 51. Physical agentsCOLDImpact of cold weather Frostbite(numbness of skin,skin appears whitish andwaxy) Influenza(flu,headache,runny nose ) Hypothermia(body temp falls below 37)HEATHeat disorders Heat cramps(painful muscle contraction begins afterstopping exercise in heat) Heat syncope(sudden fainting occurs while standing inheat for 15 to 20 mints) Heat edema(mild swelling of hands and feet) Prickly heat/heat rash(small red itching lesions on skincaused by obstruction of sweat ducts)
52. 52. RADIATIONSEffect of radiations such as x rays areused for detection but their excessiveuse can cause cancer similarlyexposure to UV light can also causecancer
53. 53. CHEMICALAGENTS/INANIMATESThe chemical agents mostly affected peoplework in an industry & exposure to suchchemicals lead todiseases(fumes,alkaloids)CONTACT WITH SKIN: Urticaria ItchingTHROUGH INHALATION: Severe coughing Chest pain Dyspnea
54. 54. THROUGH INGESTION: Vomiting (by CO poisoning)MECHANICAL AGENTS InjuryAccidentsMachinery
55. 55. NUTRITIONAL AGENTSDeficiency of these agents affectingpeople of all genders and ages . Theynot only cause specific diseases buteffect the quality of lifeThese are the nutritional agents:VitaminsMineralsProteinsCarbohydrates
56. 56. Diseases which are caused bydeficiency of the nutritional agentsagents:Osteoporosis(by the deficiency of ca)Anemia (by deficiency of iron)Scurvy (deficiency of vitamin C)Marasmus (deficiency of proteins)Acidosis ( deficiency ofcarbohydrates)
57. 57. Susceptible hostHost factors1)Demographic:Study of human population & how theychange & how they becomeunhealthy. E.g. age , sex ,ethnicity(common characteristic of agroup of people)2)Genetics/hereditary:Transmission and variation of inheritedcharacteristic. E.g. hypertension ,diabetes
58. 58. 3)Immunity:State of being insuscepectible tosomething.When there is little to no immunity withina population, the disease spreadsquicklyE.g. measles in children4) SOCIAL AND ECONIMICAL:The social & economic factors has asignificant effect on their health andwellbeing. E.g lungs cancer in adults due
59. 59. Environmental factorSeasons/weather:also affect the humane healthe.g. in rainy seasons malaria can occurSimilarly there is cold in winters.Allergy due to pollens.
60. 60. DYNAMICS OF DISEASETRANSMISSIONExistence of Source of infection orreservoir is starting point.DEFINITION OF RESERVOIR:Any person , animal , plant , soil in whichinfectious agent survives and multiply insuch a way that it can be transmitted.RESERVOIRHuman reservoirAnimal reservoirNon living reservoir
61. 61. Human reservoir:It may be CASE and CARRIERCase:Case is a person who has a particulardisease. it can be identified throughsigns and symptoms of the disease ,through diagnostic test or physicalexamination e.g patient of TBCarrier:Carry the organism of disease. Personmay be infected but not clinical diseased.E.g hepatitis(in this virus inactivate forthe time being but can be activated atany stage of life)
62. 62. Animal reserviorAlso called zoonosesAn animal become reservior whendisease which is transmitted throughanimal infected most of the populationCausative agent of disease surviveand multiply in that animale.g influneza
63. 63. Non living reservoirIncludes soil , water etcSoil contains bacteria which causetetnausWater contains microorganism(protoza) causing differentdiseases like malaria dengue.
64. 64. MODE/ROUTE OFTRANSMISSION Infectious disease can spread in a variety ofways , through air, food.Through DIRECT & INDIRECT contact with otherperson, objects skin and mucous membrane ,saliva, urine , blood and body secretions Through contaminated food and water
65. 65. ROUTES OF TRANSMISSIONDIRECTDirect contactVerticle transmissionDroplet infectionAnimal bite transmissionContact with soil
66. 66. INDIRECTAirborneVehicle borneVector borneFormite borneHand borne
67. 67. DIRECTTRANSMISSION Immediate transfer of the pathogen oragent from a host/reservoir to asusceptible host Can occur through direct physical contactor direct personal contact such as touchingcontaminated hands, kissing or sex Direct person-to-person contact with theskin or bodily fluids of a diseased person.Examples are dysentery, boils, and severalairborne diseases
68. 68. Mucus-to-mucus contact by kissing or sexualintercourse. Examples include sexually transmitteddiseases (STDs), infectious mononucleosis, andhepatitis BDirect contact with the skin, flesh (raw or notthoroughly cooked), saliva, or other bodily fluids ofdomestic or wild animals. Examples are rabies,plague, anthrax, tularemia, and trichinosis.
69. 69. Horizontal disease transmission fromone individual to another in the samegeneration (peers in the same agegroup). Horizontal transmission canoccur by either direct contact (licking,touching, biting), or indirect contact air cough or sneezeVertical disease transmission passinga disease causing agent vertically fromparent to offspring, such as perinataltransmission
70. 70. DROPLET INFECTIONDroplets or dust particles carry thepathogen to the host and infect itSneezing, coughing, talking all spraymicroscopic droplets in the air
71. 71. INDIRECT TRANSMISSIONpathogens or agents are transferred orcarried by some intermediate item ororganism, means or process to asusceptible host
72. 72. Indirect transmissionAirborne Also known as the respiratory route, and theresultant infection can be termed airborne disease. Ifan infected person coughs or sneezes on anotherperson the microorganisms, suspended in warm,moist droplets, may enter the body through the nose,mouth or eye surfaces. Diseases that are commonlyspread by coughing or sneezing include:ChickenpoxCommon coldInfluenzaMumps
73. 73. Waterborne/vehicles borneTransmission of communicable diseasethrough water, food ,milk , blood or anyother substancesInfection agent transmitted fromreservoir to susceptible host
74. 74. Vector borne (3rd organism)an organism called vector transmitt causativeagent of diseases from infected person tonon infected individualE.G mosquite,rat, lice, cockroach carrydiseases like malaria, yellow fever etc
75. 75. FECAL-ORAL TRANSMISSIONDirect contact is rare in direct route, forhumans at least. More common are theindirect routes; foodstuffs or waterbecome contaminated (by people notwashing their hands before preparingfood, or untreated sewage beingreleased into a drinking water supply)and the people who eat and drink thembecome infected. This is the typicalmode of transmission for the infectiousagents of (at least):CholeraHepatitis A
76. 76. FOMITE BORNE:Fomites are inanimate objects that canbecome contaminated with infectiousagents and serve as a mechanism fortransfer between hosts. The classicexample of a fomite is a park waterfountain from which many people drink.Infectious agents deposited by oneperson can potentially be transmitted toa subsequent drinker. However, manyobjects that we come into contact withcan serve as fomites; doorknobs,elevator buttons, hand rails, phones,writing implements, keyboards, toys in aday care center, etc. Even a stethoscopecan serve as a fomite if it isn't cleansed.
77. 77. Methods of preventionor control ofcommunicable disease:
78. 78. Communicable diseases: A disease which is transmitted fromone person to another directly orindirectly through the infectious agentlike food, air, water, dust etc.As discussed earlier that agent , mode oftransmission and host are very important forthe spread of the disease if any of thesecomponent is missing then disease cannot bespread. Therefore measure should be taken tocontrol these components , so as to preventthe spread of disease.
79. 79. 1)Controlling the source ofinfection:the most desirable control measure would be toeliminate the reservoir or source if that could bepossible. Elimination of the animal reservoir may bepretty easy i.e bovine ,TB, Brucellosis but is notpossible in humans.1. EARLY DIAGNOSIS: The first step in the control of communicablediseases its rapid identification & accuratediagnosis of disease e.g. measles, chicken pox If disease is properly treated then thesource and disease agent is destroyed & thechances of the spread of disease will beminimised.
80. 80. Early diagnosis is needed fora. The treatment of patientsb. For epidemiological investigations for example totrace the source of infection from the known caseto the unknown or the primary source of infectionc. To study the time, place and person distribution(descriptive epidemiology)d. For the institution of prevention and controlmeasures
81. 81. 2.NOTIFICATIONOnce a disease has been detected or evensuspected, it should be notified to the local healthauthority whose responsibility is to put into operationcontrol measures.it is an important source of epidemiologicalinformation. It enables early detection of diseaseoutbreaks, which permits immediate action to betaken by the health authority to control their spread.Notifications of infectious diseases is made bya. Attending physicianb. Head of the family
82. 82. 3. EPIDEMIOLOGICAL INVESTIGATIONSAn epidemiological investigation is called forwhenever there is disease outbreak.These investigations covers the:a. Identification of the source of infectionb. Factors influencing its spread in communityThese may includea. Geographical situationb. Climate conditionc. Sociald. Behavioral patternse. Character of the agentf. Sourceg. Vectorsh. Vehiclesi. Susceptible host population
83. 83. 4.ISOLATION:It is an oldest communicable disease controlmeasure.It is defined as separation, for the period ofcommunicability of infected persons from others insuch places & under such conditions, as to preventor limit the direct or indirect transmission ofinfectious agentTYPES:There are several types of isolation which vary withthe mode of spread and severity of the diseasea. Standard isolationb. Strict isolationc. Protective isolationd. High security isolation
84. 84. WAYS OF ISOLATION:a. In rural areas hospital isolation is better thanhome isolation because it is particularly difficult inthese areas. As in some situations such ascholera outbreaks the entire village has to beisolatedb. Isolation can also be achieved by ringimmunization that is encircling the infectedpersons with a barrier of immune persons throughwhom the infection is unable to spread. Eg. Thismethod was used worldwide to eradicatesmallpox in 1960s or 1970sADVANTAGES:a. Protection of communityb. Control of some infectious diseases eg.Diphtheria, choleraDISADVANTAGES:
85. 85. It has failed in the control of diseases such as leprosy,TB and STDsIn these cases physical isolation has been replaced bychemical isolation.The duration of isolation is determined by the durationof communicability of the disease and the effect ofchemotherapy on infectivity.EXAMPLES: Chickenpox.duration of isolation: until all lesionscrusted; usually about days after onset of rash Hepatitis: 3 weeks Influenza: 3 days after onset Polio: 2 weeks in adults, 3 weeks in pediatric Today isolation is recommended only when the risk oftransmission of the infection is exceptionally serious.
86. 86. 5. TREATMENT:Many communicable diseases have been tamed byeffective drugs.The object of treatment is to kill the infectious agent whenit is still in the reservoir i.e before it is disseminated.Treatment reduces the:1. Communicability of disease2. Cuts short the duration of illness and3. Prevents development of secondary casesTYPES:a. Individual treatmentb. Mass treatment
87. 87. 2)INTERRUPTION OFTRANSMISSION:A major aspect of communicable disease controlrelates to BREAKING the chain of transmission.e.g. Water can be a medium for transmission ofmany diseases as Hepatitis A, Dysentery, Choleraso it should be properly disinfected.Human excreta should be disposed off in a sanitarywayFood borne diseases in areas having low standardsof sanitation so food should be protected.
88. 88. Overall standard of living should be improvedVECTOR- BORNE: control measures should bedirected primarily at the vector and its breedingplaces. Mosquitos ,flies, stray dogs and otherinsects ,rodents and stray dogs should bedestroyed.All discharges of patients should be disposed offFOOD- BORNE: Clean practices, hand washing,adequate cooking, prompt refrigeration of preparedfood and withdrawal of contaminated foodTransmission of sexually transmitted diseases canbe prevented by using mechanical contraceptives
89. 89. 3. The Susceptible Host:The third link in the chain of transmission is thesusceptible host or people at risk. They may beprotected by one or more of the following strategies:IMMUNITY AND IMMUNIZATION: HISTORY: Before polio vaccine became available in 1955,58,000 cases of polio occurred in peak years. of these cases resulted in permanent paralysis Prior to measles vaccine in 1963, 4,000,000cases per year Immunization of 60 million children from 1963-1972 cost $180 million, but saved $1.3 billion Mumps used to be the leading cause of childdeafness 10% of children with diphtheria died
90. 90. According to CDC, unless 80% or greater ofthe population is vaccinated, epidemics canoccur.Three types of immunity possible in humans: Acquired Immunity obtained by having had adose of a disease that stimulates the naturalimmune system or artificially stimulating immunesystem Active Immunity body produces its own antibodiescan occur through a vaccine or in response to having asimilar diseaseSimilar to acquired Passive Immunity (natural passive) acquiredthrough transplacental transfer of a mothersimmunity to diseases to the unborn child (also viabreastfeeding)can also come from the introduction of already producedantibodies into a susceptible case
91. 91. When there islittle to noimmunitywithin apopulation,the diseasespreadsquickly
92. 92. HerdImmunitytheresistance apopulation orgroup (herd)has to theinvasion andspread of aninfectiousdisease
93. 93. Diseases for which vaccines areusedAnthraxChicken poxCholeraDiphtheriaGerman measles(rubella)Hepatitis A & BInfluenzaMalaria (in process)MeaslesMeningitisMumpsPlague Pneumonia Polio Rabies Small pox Spotted fever Tetanus Tuberculosis Typhoid Fever Typhus Whooping Cough Yellow Fever
94. 94. EpidemiologicalMethods
95. 95. Study Design:Study design is a specific plan or protocolfor conducting a study which allows the investigatorto translate the conceptual hypothesis into anoperational one.Hypothesis:It is an educated guess about an associationthat is testable in a scientific investigation
96. 96. OBSERVATIONAL STUDIESDescriptive epidemiologyCase reports /case seriesCross sectional studiesLongitudinal studiesAnalytical epidemiologyCase controlCohort studiesEXPERIMENTAL STUDIESClinical Trials
97. 97. *Observational Studies*Do not have control over the circumstancesAllow nature to take its own course, theinvestigator measures but does not intervene1.Descriptive Epidemiology:In a descriptive study, the epidemiologistcollects information to characterize andsummarize the health event or problem.It is limited to the description of theoccurrence of a disease in a population
98. 98. in the descriptive process, we areconcerned with"person" (Who was affected?)"place" (Where were theyaffected?)and time (When were theyaffected?)Basic Triad of Descriptive EpidemiologyTHE THREE ESSENTIAL CHARACTERISTICS OF DISEASEWE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY ARE:PERSONPLACETIME
99. 99. Descriptive epidemiology study the patternsor trends in a situation but not a cause aneffect linkages among different elements. Examining the distribution of a disease in apopulation, and observing the basic featuresof its distribution in terms of time, place andperson. It helps in the generation of hypothesis. Measurement of disease in terms ofmortality, morbidity, disability. It is the first phase in the investigation
100. 100. Procedure:The procedure involve in such studies includesDefining the population to be studiedDefining the disease under studyDescribe the distribution of disease in relation to TimePlace & PersonMeasurement of disease in terms of mortality,morbidity and disabilityFinally formulation of etiological hypothesis
101. 101. Defining thePopulation1) 1.Descriptive studies are investigations ofpopulations not individuals2) 2.The defined population can be:o The whole populationo A representative sampleDEFINING THE DISEASE UNDER STUDY:The epidemiologist whose main concern is toobtain an accurate estimate of the disease ina population needs a definition that is bothprecise and valid to enable him to identifythose who have the disease from those whodo not.
102. 102. DESCRIBING THE DISEASEDescribes the occurence and distribution of diseaseby time, place and person and identifying thosecharacteristics associated with presence or absenceof the disease in individualsTIME PLACE PERSONYear, season Climaticzonesage Birth orderMonth, week Country,regionsex Family sizeDay, hour ofonsetUrban/rural MarritalstateHeight,weightduration Towns, cities Occupation,socialstatus,educationBP, bloodcholestrol,personalhabbits
103. 103. TIME DISTRIBUTIONThe pattern of disease may be described by thetime of its occurance, i.e week, month, year, dayof week etc.Epidemiologists have identifies three kinds oftime trends or fluctuations1. Short term fluctuations2. periodic fluctuations3. Long term fluctuations
104. 104. PLACE DISTRIBUTIONBy studying the distribution of the disease indifferent populations we gain perspective indisease patterns not only between countries butalso within countries. Geographic patternsprovide the causes of the disease.a. International variationsb. National variationsc. Rural-urban differencesd. Local distributions
105. 105. PERSON DISTRIBUTION:The disease is further characterized by definingthe person who develops the disease by variousfactors: Age Sex Ethnicity Martial status Occupation Stress migration
106. 106. Measurement of Disease:The amount of the disease disease load in thepopulation.This information should be availablein terms of mortality, mobidity, disability and soon.Measurement of Mortality is straightforward.Morbidity has 2 aspects, Incidence prevelence
107. 107. 1) Case series/ Case report:A.Case Report:The case report is the presentation of the experience of a singlepatient. A case report is a detailed report of the symptoms , signs ,diagnosis , treatment, and follow-up of an individual patient . Casereports may contain a demographic profile of the patient, but usuallydescribe an unusual or novel occurrence. Some case reports alsocontain a literature review of other reported cases. Case reports areoften referred to as Hypothesis-generating because these bring forthevidence that supports a Hypotheses or conclusion.EXAMPLE The presentation of the medications for the patientthat were administered until the development of aplastic anemiasuggest that 1 of these may have caused it. However it is notconcluded that another patient taking the same could be at riskbecause of many other factors eg insecticides, viral infection whichmay not b a part of the medical report
108. 108. B. CASE SERIES:When the common experiences of morethan one patient are presented, this isreferred to as case series. Greater thenumber of experiences stronger theevidences.EXAMPLE: if five patients developedaplastic anemia due to the same medication,this would raise questions. A good exampleis the case series of 24 patients showingvuvular heart abnormalities from concurrentfenfluramine which lead to its withdrawalfrom the market
109. 109. Most case reports are on one of six topics:i. An unexpected association betweendiseases or symptoms .ii. An unexpected event in the course ofobserving or treating a patient.iii. Findings that shed new light on the possiblepathogenesis of a disease or an adverseeffect.iv. Unique or rare features of a disease.v. Unique therapeutic approaches.vi. A positional or quantitative variation of theanatomical structures.Advantage:Case series/Case report may be thefirst to provide clues in identifying a new diseaseor adverse health effect from an exposure.
110. 110. 2) Cross-sectional studies: Also known as prevelance study. It is thesimplest form of the observation study.Prevelence is the frequency of cases at a giventime.They provide a snap shot of the frequency and characteristicsof a disease in a population at a particular point in time.It is a single examination of a cross section of population at onetime and the results can be projected on the whole populationDoesnot tell us about the history of the disease but only thedistributionThis type of a data can be used to assess the prevalence ofacute or chronic condition in a population. But mostly forchronicHowever since exposure & disease status are measured atthe same point in time, it may not be possible to distinguishwhether the exposure proceeded or followed the disease andthus Cause and effect are not certain. For example the study ofhypertension
111. 111. Advantages: Several outcomes Short durationDisadvantages:Not feasible for rare diseasesProvide less information about the history ofthe disease or the rate of occurance
112. 112. Longitudinal studies:It involves a repeated observation ofthe same variables over longer period of time, oftenmany decades by means of follow-up examination.Much like a cine film. Also known as INCIDENCEstudy. Incidence is the development of new cases in apopulation at risk. It is often used in psychology to studydevelopmental trends across the life span and insociology to study life events throughout life timeand generation.ADVANTAGES: 1. study the natural history of disease2. Risk factors3. Incidence rateDISADVANTAGES: 1. difficult to organize2. Time consumingFor example the study of bp in a community will revealthe normal values rather than the abnormal onesrelated to the disease
113. 113. FORMULATION OF HYPOTHESISBy studying the distribution of the disease andutilizing the techniques of descriptiveepidemiology, it is possible to formulatehypotheses.Example: cigerrete smoking causes lungcancer. This is incomplete hypothesisComplete hypothesis: the smoking of 30-40 cigarettes per daycauses lung cancer in 10 percent of thesmokers after 20 years of exposure
114. 114. Advantages of descriptive epidemiology:It provides clues of etiology of disease.Provide data regarding magnitude and type ofdisease problems in community in terms ofmorbidity ,mortality ,rates & ratios.Background data for planning ,organizing,preventive and curative servicesContribute to reasearch by describingvariations in the disease occurance by time,place and person
115. 115. ANALYTICAL EPIDEMIOLOGYIn analytical studies the subject of interest is theindividual within the population. The object is notto formulate but to test hypothesis.Once we know the answers to the questions indescriptive epidemiology, we can enter the realmof analytical epidemiology and ask how andwhy these people were affected.Testing a specific hypothesisabout a relationship of a disease to a specificcause.Analytical studies comprise 2 distinct types1. Case control study2. Cohort study
116. 116. Case control studyIt refers to as Retrospective studies and theyserve as first approach to test any casualhypothesis.Emerged as the permanent method ofepidemiologyCase control studies are often used to identifyfactors that may contribute to a medical conditionby comparing subjects who have thatdisease(cases) with patients who dont have thatdisease(control group) but are otherwise similar.The control group should ideally come from thesame population.Case control studies has different features: Both the exposure ( cause) an outcome (effect)have occurred before the study is taken up. The study proceeds backwards from the effectto cause
117. 117. Case individuals with particular diseaseControl individuals without particular diseaseBASIC STEPS1. Selection of cases and controls2. Matching3. Measurement of exposure and4. Analysis and interpretationBIAS:Systemic error in the determination of the associationbetween exposure and diseaseBias due to memory recallSelection biasInterviewers bias
118. 118. Advantagescan obtain findings quicklycan often be undertaken with minimalfundingefficient for rare diseasesAllows the study of several differentaetiological factors eg. Smoking, physicalactivity etc.No attrition problems, because case controlstudies donot require follow up of individualsinto the futuregenerally requires few study subjectsDisadvantagescannot generate incidence data, can onlyestimate relative risksubject to bias
119. 119. COHORT STUDIESCohort:Cohort can be defined as a group of peoplewhich shares a common characteristics orexperience with in a defined time. Eg.Birth cohort: group of people born on the same dayExposure cohort : persons exposed to a commondrug or vaccineDISTINGUISHING FEATURES:1. Cohorts are identified prior to the appearance ofthe disease under investigation2. The study groups, so defined, are observed overa period of time to determine the frequency ofdisease among them3. The study proceeds forward from cause to effect
120. 120. FRAMEWORK OF COHORTSTUDYStudy cohort: exposed to a particular factorControl cohort: not exposedExample: smokers and non smokers associated withlung cancerGENERAL CONSIDERATIONS:1. The cohorts must be free from the disease2. Both the groups should be equally susceptible tothe disease under study eg. Males over 35 yearswould be appropriate for studies on lung cancer3. Both the groups should be comparable in respectof all the possible variables which may influencethe frequency of the disease
121. 121. ELEMENTS OF COHORT:1. Selection of study subjects2. Obtaining data on exposure3. Selection of comparison groups4. Follow up5. analysis
122. 122. TYPES OF COHORT STUDIESPROSPECTIVE COHORT STUDIES:More preferred type of study but expensive.a prospective or current cohort is one in which theoutcome(disease) has not yet occurred at the timethe investigation beginsBegin in the present and continue into futureEXAMPLE:Study cohort: uranium minersControl cohort: non-minersDisease: lung cancerThe principal finding was that the uranium minershad an excess frequency of lung cancer campared tonon-miners. since the disease had not yet occurredwhen the study was undertaken this is theprospective cohort design
123. 123. RETROSPECTIVE COHORT STUDIESalso known as historical cohort studyExposure and outcome have already occurred at the start of thestudy. Pre-existing data, such as medical notes, can be used toassess any causal links, so lengthy follow-up is not required.This type of cohort study is therefore less time consuming andcostly, but it is also more susceptible to the effects of bias. Forexample, the exposure may have occurred some yearspreviously and adequate reliable data on exposure may beunavailable or incomplete. In addition information onconfounding variables may be unavailable, inadequate ordifficult to collects* More economical and produce results more quickly thanprospective cohort studies
124. 124. COMBINATIONS OF PROSPECTIVE ANDRETROSPECTIVE COHORT STUDIES:In this type of study these elements are combinedFor example: patients who received large dosesof radiation therapy for ankylosing spondylitis. Theoutcome was death due to aplastic anemia. Theyfound that the death from aplastic anemia was higherin their cohort than the general population. Thus aprospective component was added to identify deathsin the subsequent years
125. 125. Advantages: Establish sequence of events Short duration Relatively cheap Can study several outcomes Dose response ratios can be estimatedDisadvantages: Often requires large sample sizes Not feasible for rare diseases Requires long period of follow up The study itself may alter peoples behaviour It is not unusual to loose a substantial proportion ofthe original cohort,they may migrate or loose interest
126. 126. Strengths in Cohort vs. Case-control? Cohort study : Rare exposure Examine multiple effects of a single exposure Minimizes bias in the in exposuredetermination Direct measurements of incidence of thedisease Case-control study : Quick, inexpensive Well-suited to the evaluation of diseases withlong latency period Rare diseases Examine multiple etiologic factors for a single
127. 127. ExperimentalEpidemiology:Experimental, where the epidemiologists havecontrol over the cicumstances from the start.It is the study of the relationships ofvarious factors determining the frequency anddistribution of diseases in a community. Itprovides a specific proof. It can provide thestrongest evidence for cause and effect.
128. 128. Types Of Trials:TrialControlled Not controlledRandomised Not randomisedBlinded Not blinded
129. 129. Randomized controltrials(RCT):It is a specific type of scientific experiment.It is used to study a particular intervention.Subjects in the study population are randomlyallocated to intervention and control groups, andthe results are assessed by comparing theoutcome.Basic steps:Drawing a protocolSelecting a reference andexperimental populationsRandomizationManipulation or interventionFollow upAssessment of outcome
130. 130. THE PROTOCOL:Protocol specifies the aims and objectives of thestudies,criteria for the selection of the study and controlgroups,size of the sample,procedures for a location etc.Itaims at preventing bias and to reduce the sources oferrors in the study.SELECTING REFERANCE AND EXPERIMENTALPOPULATION:a. Refererence population or target population isthe population to which the findings of the trialif found successful are applicable eg. Drug,vaccine etcb. Experimental or study population is derivedfrom the reference population. The actualpopulation that participates in the experimentalstudy
131. 131. CRITERIA:a. Informed consentb. Representative of the populationc. Eligible of the trialRANDOMIZATION:Statistical procedure by which the participants areallocated into groups usually called study andcontrol to receive or not to receive the experimental,preventive or therapeutic procedureAttempt to eliminate bias and to ensure that theinvestigator has no control over the allocationThe essential difference between a randomizedcontrol trial and an analytical study is that in thelatter, there is no randomization becausedifferentiation into diseased and non-diseasedgroups has already taken place
132. 132. MANIPULATION:After formation of the groups the next step is tointervene or manipulate the study group by thedeliberate application or withdrawal or the reductionof the suspected casual factor e.g. drug vaccine etc.FOLLOW-UP:This implies the examination of the experimental andthe control groups at defined intervals of time, in astandard manner, with equal intensitySome loses to follow up are inevitable due to death,migration and loss of interest. This is known asattrition
133. 133. ASSESMENT:positive and negative results are deucedSequential analysis may be doneBIAS: may arise from the errors of assessment of theoutcome due to human element. There are 3 types:a. Subject variation: bias on the part of theparticipants who may subjectively feel better orreport improvement if they knew they werereceiving new form of treatmentb. Observer bias: observer measuring the outcomemay become influencedc. Bias in evaluation: investigator may give afavorable report of the outcome
134. 134. BLINDING:1. Single blind trial: the trial is so planned that theparticipant is not aware whether he belongs to thestudy group or control group2. Double blind trial: the trial is so palnned thatneither the doctor nor the particioant is aware ofthe group allocation and the treatment received3. Triple blind trial: the participant, investigatior andthe person analysing the data are all blind
135. 135. SOME STUDY DESIGNS:1. concurrent parallel study designs: one group isexposed to the treatment and the other grop is notexposed2. Cross over type of study design: the study groupreceives the treatment under consideration andthe control receives the alternate, placeboCannot be used ifa. It cures the diseaseb. Only effective on a certain stage
136. 136. TYPES OF RANDOMIZED CONTROLTRIALS:1. Clinical trials2. Preventive trials3. Risk factor trials4. Cessation trials5. Trial of aetiological agents
137. 137. NON-RANDOMIZED CONTROLTRIALSIn non randomized controlled trials, the control groupis predetermined (without random assignment) tobe comparable to the program group.Because the study groups are opportunistically ratherthan randomly composed, study groupcharacteristics (age, sex) may not be balancedbefore (at baseline) the study begins.1. Uncontrolled Trials: trials with nocomparison group
138. 138. 2. NATURAL EXPERIMENTS:Where the experimental studies are not possible inhuman populations the epidemiologist seeks toidentify natural circumstances that mimic anexperiment. For example:1. smokers and non-smokers have naturallyseparated themselves into two groups2. cholera
139. 139. USES:1 To study the history of the diseaseTrends of a disease for the prediction of trend Results of studies are useful in planning forhealth services and public health2. Community diagnosisWhat are the diseases, conditions, injuries,disorders, disabilities, defects causing illness,health problems, or death in a community orregion3. Look at risks of individuals as they affectpopulationsWhat are the risk factors, problems, behaviorsthat affect groupsGroups are studied by doing risk factorassessments: health screening , medical examsand disease assesments4. Assessment, evaluation and researchHow well do public health and health servicesmeet the problems and needs of the populationEffectiveness; efficiency; quality; access;availability of services to treat, control or preventdisease
140. 140. 5. Completing the clinical pictureIdentification and diagnostic process toestablish that a condition exists or that aperson has a specific diseaseCause effect relationships are determined,e.g. strep throat can cause rheumaticfever6. Identification of syndromesHelp to establish and set criteria to definesyndromes, some examples are: fetalalcohol, sudden death in infants, etc.7. Determine the causes and sources ofdiseasesFindings allow for control prevention, andelimination of the causes of disease,conditions, injury, disability, or death