Presentation on theme: "DISEASE EPIDEMIOLOGY Dr . A.K.AVASARALA MBBS, M.D."— Presentation transcript:
1 DISEASE EPIDEMIOLOGY firstname.lastname@example.org Dr . A.K.AVASARALA MBBS, M.D. PROFESSOR & HEADDEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGYPRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P..INDIA:Author profile :-After medical graduation, worked for 17 years in the field as primary care physician in primary health centres, area hospitals, mobile medical units, cholera combat team, filarial control project, casualty department, divisional secondary care hospitalsThen completed post graduation in public health medicine/preventive &social medicine &epidemiology and teaching medical graduates and post graduates, nursing students, physiotherapy students, primary care personnel for the last 15 years.At present working as Professor & Head of the department of Community medicine & Epidemiology since 15 years and practicing and contributing to the cause of epidemiological spread and growth in India (life ambition) as Indian super course epidemiology developer.Other EIGHT super course lectures of mine can be accessed at
2 PROMPT DISEASE IS STILL A MYSTERY SOME DISEASES KILL AND SOME WONT KILLSOME ARE SHORT LIVED WHILE OTHERS ARE LONG LIVEDSOME ARE TREATABLE AND SOME ARE NOTSOME ARE CURED BY MIRACLES (TO ACHIEVE SAINTHOOD, THERE ARE INSTANCES OF CURING BY MIRACLES)WE THINK WE KNOW EVERY THING ABOUT DISEASE DYNAMICSBUT STILL THERE ARE GAPS.ARE THEY GAPS IN OUR UNDERSTANDING OR IN REALITY?THIS ACTUALLY PROMPTED ME EXPRESS MY DOUBTS AND TO DEVELOP THIS LECTURESECONDLY, I WISH TO GIVE A GROSS PICTURE ABOUT THE DISEASE TO THE STUDENT DISCUSSING THE PRESENT REALITIES.
3 LEARNING OBJECTIVES WHAT IS DISEASE? THE STUDENT SHOULD LEARN DISEASE PROCESSWHAT IS DISEASE?WHAT ARE THE THEORIES OF CAUSATION OF DISEASE?HOW IS IT INITIATED?HOW IS IT CAUSED?HOW IS IT TRANSMITTED? HOW IT SPREADS?HOW IT IS DISTRIBUTED? AND WHY?HOW IT CAN BE PREVENTED?HOW IT CAN BE ERADICATED?
4 PERFORMANCE OBJECTIVE STUDENT CAN USE EPIDEMIOLOGICAL APPROACH TO PREPARE A LESSON PLAN BY MAKING USE OF VON KIPLING'S SIX HONEST SERVING MEN (WHAT, WHY, WHEN, WHERE, WHOM AND HOW) TO DEVELOP A LECTURECONTEXTS TO UTILIZE SIX HONEST SERVINGMEN WHILE PREPARING LESSON PLAN ON ANY TOPICWHAT =DEFINITIONWHY= PUBLIC HEALTH SIGNIFICANCE(MAGNITUDE)HOW=PROCESSWHEN= TIME TRENDSWHERE= PLACE DISTRIBUIONWHOM=PERSONS USUALLY AFFECTED
5 WHAT EXACTLY IS A DISEASE IS STILL A ? IS IT A SEQUENCE OF PATHOLOGICAL CHANGES AND THEIR EFFECTS OCCURRING IN THE INDIVIDUAL?IS IT A COMPOSITE OF EFFECTS DUE TO DISTURBANCE IN MAN’S RELATIONSHIP WITH HIS ENVIRONMENT BY AN AGENT/FACTOR?IS IT AN AFTER-EFFECT OF A GERM’S EFFORT TO MAINTAIN ITS OWN RACE BY MULTIPLYING AND SURVIVING AS A PARASITE IN MAN?IS IT A DISTURBED MAN’S INTERNAL AND EXTERNAL ENVIRONMENT DUE NEGATIVE LIFE STYLES?IS IT THE DESTINED EFFECT ACQUIRED FROM THE FOREFATHERS?IS IT A GENE AND ENVIRONMENTAL INTERACTION?ALL ARE TRUE TO SOME EXTENT BUT NONE IS THE COMPLETE ANSWER. THIS SHOWS THAT DISEASE HAS GOT AS MANY FACES AS GOD AND VERY DIFFICULT TO DEFINE.
6 DISEASE CAN BE SIMPLY EXPLAINED AS DIS AT EASE OR ILL HEALTH WHAT IS A DISEASE?DISEASE CAN BE SIMPLY EXPLAINEDAS DIS AT EASE OR ILL HEALTHSOME DESCRIBE IT AS DISTURBANCE IN EQUILIBRIUM BETWEEN MAN AND HIS TOTAL ENVIRONMENT.IT IS ALSO DESCRIBED AS OPPOSITE OF HEALTH WHEREIN SOME PART OR ORGAN OF THE HUMAN BEING IS DISTURBED OR AFFECTED AT SOME LEVEL, FROM CELLULAR TO ORGAN OR FUNCTIONAL LEVEL.SOME THINK LIBERALLY THAT SICKNESS, IMPAIRMENT, DISABILITY AND HANDICAP ARE SYNONYMOUS WITH THE DISEASE.USUALLY IMPAIRMENT IS CONSIDERED AS LOSS OF ANATOMICAL PART OF THE BODY, DISABILITY AS FUNCTIONAL LOSS, HANDICAP AS A SOCIAL LOSS AND SICKNESS AS A SOCIAL ROLE PLAYED DUE TO ILLNESS. ALL THESE ARE THE CONSEQUENCES OR EFFECTS OF A DISEASE.
7 HOW THE DISEASE IS CAUSED? SUPERNATURAL THEORY OF DISEASEECOLOGICAL THEORYGERM THEORYMULTIFACTORIAL CAUSATION THEORY
8 NO UNANIMOUS OPINIONAT LEAST 10% OF THE PEOPLE IN DEVELOPED COUNTRIES AND 30% IN DEVELOPING COUNTRIES STILL BELIEVE IN SUPERNATURAL ORIGINEVEN TODAY SUPERSTITIONS ARE BECOMING MAJOR OBSTACLES IN DISEASE CONTROLMOST OF THE LITERATES VIEW THAT DISEASE IS THE RESULT OF MICROBESMOST OF THE UNEDUCATED PEOPLE (90%) BELIEVE THAT DISEASE IS DUE TO BAD PHYSICAL ENVIRONMENTVERY FEW PEOPLE KNOW AND ACCEPT THAT IT IS DUE TO THEIR OWN NEGATIVE LIFE STYLES (FAULTS)SCIENTIFIC PEOPLE BELIEVE IN ALL , INCLUDING SUPERNATURAL ORIGIN AS THEY CANNOT EXCLUDE IT AS A CAUSE OF THE DISEASE.ARE THE CONCEPTS OF ORIGIN OF THE DISEASE REALLY CHANGING OR MIXING ?
9 SUPERNATURAL THEORY OF DISEASE: IN THE EARLY PAST, THE DISEASE WAS THOUGHT MAINLY DUE TO EITHER THE CURSE OF GOD OR DUE TO THE EVIL FORCE OF THE DEMONS. ACCORDINGLY, PEOPLE USED TO PLEASE THE GODS BY PRAYERS AND OFFERINGS OR USED TO RESORT TO WITCHCRAFT TO TAME THE DEVILS.BOTH THESE BELIEFS ARE PERPETUATED BY IGNORANCE, ILLITERACY AND POVERTY PREVALENT NOT ONLY IN THOSE TIMES BUT ALSO IN THE PRESENT DAYS.THIS SUPERNATURAL ORIGIN OF THE DISEASE TOOK SUCH A STRONG ROOTS IN THE PEOPLES’ MINDS MAKING THE CONTROL AND ERADICATION OF ANY DISEASE DIFFICULT EVEN TODAY AS IT IS POTENTIALLY INFLUENCED BY THE INDIVIDUAL ‘S PERSONAL BELIEFS AND ATTITUDE.
10 ECOLOGICAL THEORYAROUND 463 BC, HIPPOCRATES IS THE FIRST EPIDEMIOLOGIST WHO ADVISED TO SEARCH THE ENVIRONMENT FOR THE CAUSE OF THE DISEASE.These human ecological concepts, i.e. the study of human relationship with environment made the later thinkers search the cause in environment. His advice in his treatise on “Airs, Waters and Places” elucidates vividly the role of environmental influences upon and relationships with human being in causing the disease.HE RIGHTLY ADVISED TO SEARCH AIR, WATER AND PLACES FOR THE CAUSE OF A DISEASE.It is the first scientific approach or reasoning regarding disease causation.He loaded the gun of scientific thinking about disease causation while Pasteur, Henle, Koch and Pettenkoffer pulled the trigger.
11 ENVIRONMENTAL INFLUENCE INTERACTIONS AMONG HUMANS, OTHER LIVING CREATURES, PLANTS, ANIMALS, MICRO ORGANISMS, ECOSYSTEMS, AND CLIMATE, GEOGRAPHY, AND TOPOGRAPHY ARE SO COMPLEX THAT DESPITE MUCH STUDY WE ARE OFTEN UNCERTAIN WHAT IS REALLY HAPPENING.
12 ECOLOGICAL DETERMINANTS OF DISEASE MCKEOWN HAS POINTED OUT, IMPROVED HEALTH OWES LESS TO ADVANCES IN MEDICAL SCIENCE THAN TO THE OPERATION OF NATURAL ECOLOGICAL LAWSSELF –ELIMINATION OF THE DISEASEBEING WELL-FED, BETTER HOUSED, WELL-INFORMED, AND SEPARATED FROM OTHERS BY ENOUGH SPACE TO REDUCE THE PROBABILITY OF PERSON-TO-PERSON TRANSMISSION OF INFECTION, ALL HELPED TO REDUCE THE BURDEN OF PREMATURE DEATH.
13 GERM THEORYGerm theory: Microbes (germs) were found to be the cause for many known diseases. Pasteur, Henle, Koch were the strong proponents of microbial theory after they discovered the micro-organisms in the patients’ secretions or excretions.ROBERT KOCH
14 HENLE-KOCH POSTULATES Henle and Koch have postulated thatEach disease will be caused by a germWithout that germ that disease will not be causedBy introducing that germ , that disease can be caused in animals experimentally,And that germ can again be isolated from that sick animal experimented with.These postulates are rigid and strongly confirm one-one theory, i.e. unifactorial causation of the disease. Though these are true to some extent for infectious diseases, they cannot explain the etiology of all diseases, particularly non-infectious diseases.Moreover it was found that a single cause can cause several diseases and several causes can cause a single disease refuting 1-1 relationship even with infectious diseases.. Germ cannot be found in certain diseases, particularly, non-communicable diseases further contradicting the postulates.Sometimes, disease is found even in the absence of a germ and vice versa e.g. sputum negative tuberculosis
15 MULTIFACTORIAL CAUSATION THEORY PETTENKOFFERSTATED THAT AGENT, HOST AND ENVIRONMENTAL FACTORS WILL ACT AND INTERACT SYNERGISTICALLY AND ACT AS JOINT INDEPENDENT PARTNERS IN CAUSING THE DISEASE.PETTENKOFFER TOOK A RIDE ON THE UNIFACTORIAL THEORY STATING THAT KOCH’S POSTULATES CANNOT EXPLAIN THE NON COMMUNICABLE DISEASE CAUSATION WHERE ONE CANNOT FIND A GERM.HE GAVE GENERALIZED EXPLANATION APPLICABLE TO ALL DISEASES, INFECTIOUS AND NON-INFECTIOUS AS WELL THAT DISEASE IS MULTIFACTORIAL.PETTENKOFFER CONTRADICTED THE UNIFACTORIAL THEORY OF DISEASE CAUSATION AND EMPHASIZED THAT DISEASE IS MULTIFACTORIAL IN CAUSATION. SEVERAL CAUSES OR FACTORS ACTING JOINTLY, CUMULATIVELY, BY COMPLEMENTING OR IN AN UNEXPLAINED MANNER WILL LEAD TO THE DISEASE.THIS THEORY OF WEB OF CAUSATION EXPLAINS BOTH THE INFECTIOUS AND NON-INFECTIOUS DISEASES. THESE MULTIPLE CAUSES WORK THROUGH DIFFERENT GROUPS OR CONSTELLATIONS.PETTENKOFFER
16 WHEN THE DISEASE OCCURS? Agent (SEED) factorsDISEASE OCCURS ONLY WHEN THE HOST FACTORS AND ENVIRONMENTAL FACTORS MAKE THE AGENT SUFFICIENT ENOUGH TO CAUSE THE DISEASEDFOR A PLANT TO GROW, SEED MUST BE PLANTED IN A FERTILE SOIL AND SHOULD BE NOURISHED WITH WATER.SIMILARLY, THE DISEASE OCCURS ONLY WHEN THE AGENT (SEED) FINDS A SUSCEPTIBLE HOST (FERTILE SOIL) AND FAVORABLE ENVIRONMENT (SHOWER) FOR INTERACTION.Environmental factors(SHOWER)Host factors (SOIL)
17 CAUSAL CONSTELLATIONS diseaseActually, several causes form into groups or constellations to cause the disease.A necessary or principal cause will be helped and complemented by other causes (predisposing, enabling, precipitating, reinforcing causes) making it sufficient to initiate the disease. Unless a necessary cause has enough support by other causes by means of their complementing and synergistic action, that cause can never become sufficient enough for disease initiation.These causal partners will not loose their identity and individuality while complementing necessary cause but just help the necessary cause. While doing so, these causal partners form a web of cumulative and synergistic action with the necessary cause to initiate the disease.That means when a necessary cause is fully complemented with its causal partners, it becomes sufficient enough to cause the disease.Presence of a sufficient cause means that disease is initiated. This explanation is true serves for both the infectious and non-infectious disease.A F G H J KA R S T XA B C D EA L M N P QCausal constellationsA = NECESSARY CAUSEB TO X = CAUSAL PARTNERS
18 EXAMPLES LUNG CANCER IS CAUSED BY A CONSTELLATION OF CAUSES LIKE SMOKINGUNFILTERED CIGARETTES10 YEARS DURATIONAND HOST SUSCEPTIBILITYPutting on a switch, though appears to be apparent single cause resulting in lighting, it is actually the result of a group or constellation of causes, which includeswiring,electricity,unspent bulbalong with the switch.
19 TISSUE INSULT DUE TO CHRONIC IRRITATION Chronic irritation of any tissue may lead to diseaseMARJOLIN’S ULCER- in the past, barbers used to wipe their razors on their forearms frequently while shaving the beards of their clients. This chronic irritation has resulted in squamous epitheliomatous changes and cancers ( Marjolin’s ulcers) in barbersCancer cervix is more seen in multiparous women and less seen in nullipara. This may be due to chronic irritation due to sexual life for longer duration in multipara.Cancer lip is more seen with chronic smokers due to chronic irritation of the delicate lip mucosa, leading to purposeless neoplastic growthCancer stomach is more seen with those people who insult their gastric mucosa with offending agents like drugs, hot and spicy foods, alcohol etc.Cancer larynx is frequently seen with singers and teachers. who abuse their voices.Personal experience. – My own maternal uncle, who developed a habit of folding and twisting the skin on his Adam’ s apple for 40 years developed epitheilioma of skin there and died.Hence God given tissue should be respected because that greatest engineer has included in each cell , all the necessary ingredients of life.
20 PLANETS AND DISEASEIT IS WELL KNOWN THAT PLANETS (EARTH,SUN, MOON ) AND THEIR MOVEMENTS, THEIR INTER DISTANCES AND RELATIONSHIPS WILL CAUSE SEASONS OF THE YEARPLANETS’ INFLUENCE ON ORIGIN OF SEASONAL DISEASES AND THEIR CONTROL IS STILL A PANDORA BOXIn India, sciences of astronomy and astrology are 5000 years old. They describe the various affects of the planetary relationships on the health of the people.Planetary movements cause seasons of the year. They explain also the seasonal effects on health of the people.If there is no truth in it how can they survive for centuries? This origin of the disease , we have to diligently search.
21 INCUBATIONTHE AGENT INCUBATES TO ACQUIRE THE CRITICAL DENSITY TO INITIATE THE DISEASEIT MULTIPLIES OR INCREASES IN INTENSITY FOR A SPECIFIC PERIOD BEFORE BECOMING OVERT AND CLINICAL
22 DISEASE INITIATIONTHE DISEASE IS INITITED AT THE CELLULAR LEVEL WHEN THE NECESSARY CAUSE (AGENT) BECOMES SUFFICIENT I.E. COMPLIMENTED BY ITS CAUSAL PARTNERS
23 HOW IT PROGRESSES? Natural history of disease Pre-pathogenic periodDisease initiation atCellular levelIncubationPeriod/Generation timeCarrierStateNatural history of the disease is that course, the disease takes, if it is left on its own , without any interference or intervention either of preventive, promotive , curative, medical or surgical nature.A disease when it is left like that (very rare) either ends in recovery or death. It follows usually this course as shown in the slideDeathPathogenicperiodConvalescentperiod
24 HOW THE DISEASE IS TRANSMITTED? SusceptibleHost/Non –Immune/Poor herd immunityMODE OF TRANSMISSION THROUGH SOME VEHICLE OR VECTORRESERVOIR/SOURCE OFAGENTDisease transmission depends upon several factors of agent (virulence, critical density, antigenicity) host (immiunity, age, personal habits) environment (herd immunity, sanitation staus, socio economic status, climate etc.)
25 DISEASE DISTRIBUTION SHORT TERM FLUCTUATIONS, LONG TERM FLUCTUATIONS, TIME DISTRIBUTION OF THE DISEASESHORT TERM FLUCTUATIONS,LONG TERM FLUCTUATIONS,PERIODIC FLUCTUATIONS,CYCLICAL, SEASONAL, SECULAR TRENDSPLACE DISTRIBUTION:-INTERNATIONAL LEVELNATIONAL LEVELREGIONAL LEVELLOCAL LEVELPERSON DISTRIBUTION OF THE DISEASE:-AGE WISE, SEX WISE,ACCORDING TO OCCUPATION,LITERACY, IMMUNITY, RACE, ETHNICITY, MARIIED LIFE, PERSONAL BEHAVIOUR
26 CLUSTERINGTHIS PHENOMENON IS USUALLY ASSOCIATED WITH INFECTIOUS DISEASES.DISEASE OCCURS IN CLUSTERS OR GROUPS AT A PARTICULAR PLACE WHEN THE PEOPLE ARE SUSCEPTIBLE AND ENVIRONMENT IS FAVOURABLE THERE.JOHN SNOW DETECTED CLUSTERING OF CHOLERA CASES AT BROAD STREET IN LONDON AND THIS CLUSTERING PROMPTED HIM NOT ONLY TO CONDUCT HIS EXPERIMENT BUT ALSO TO REMOVE THE HAD OF THE STREET PUMP TO PREVENT EPIDEMIC.
27 ONION PEEL PHENOMENONOLD DISEASES FADE AWAY GIVING PLACE TO THE NEW ONESJUST LIKE THE LAYERS OF THE ONION, THE OLD DISEASES WANE AND GIVE PLACE TO NEWONES.INFECTIOUS ONES WILL BE REPLACED BY NON–INFECTIOUS ONES TO BE REPLACED LATERBY PERSONAL AND BEHAVIORAL PROBLEMS.JUST LIKE THE LAYERS OF THE ONION, THE OLD DISEASES WANE AND GIVE PLACE TO NEWONES.INFECTIOUS ONES WILL BE REPLACEDBY NON –INFECTIOUS ONES TOBE REPLACED LATERBY PERSONAL AND BEHAVIORALPROBLEMS.
28 DISEASE PREVENTIONPRIMORDIAL PREVENTION-- INTERVENTIONS TAKEN BEFORE THE DEVELOPMENT OF RISK FACTORPRIMARY PREVENTION -- INTERVENTIONS TAKEN BEFORE THE DISEASE IS ESTABLISHEDSECONDARY PREVENTION-- INTERVENTIONS TAKEN AFTER THE DISEASE IS ESTABLISHED-TERTIARY PREVENTION --INTERVENTIONS TAKEN TO PREVENT COMPLICATIONSAT EVERY LEVEL, PREVENTION CAN BE TRIED AND SHOULD BE TRIED.EVEN BEFORE DEATH, SOME THING CAN BE TRIED TO MITIGATE THE SUFFERING.PHILOSOPHY OF PREVENTION IS THE CORNERSTONE WHILE DEALING WITH PATIENTS IN HOSPITAL SETTING OR IN POPULATION
29 DISEASE SURVEILLANCE METHODS:- WATCHING THE DISEASE WITH SUSPICION, ATTENTION AND AUTHORITYSUSPECT UNLESS AND UNTIL IT IS DISPROVEDBE ATTENTIVE AND CAUTIOUSTRY TO GRASP THE ENTIRE NATURAL HISTORY OF THE DISEASEKEEPING TRACK OF TRENDS AND EVENTS OF THE DISEASE.METHODS:-LAYMAN REPORTINGACTIVE SURVEILLANCEPASSIVE SURVEILLANCESENTINEL SURVEILLANCESERO SURVEILLANCE
30 PUBLIC HEALTH PROBLEMDISEASE WILL BE A PUBLIC HEALTH PROBLEM WHEN IT CAUSES HIGH MORBIDITY AND MORTASLITYDEMANDS URGENT HEALTH ACTIONEITHER IN THE FORM OFCONTROLELIMINATIONERADICATION
31 DISEASE CONTROLCONTROL STRATEGY = REDUCING THE MORBIDITY AND MORTALITYA CONTINGENCY TEMPORARY MEASURE IN CASE OF EMERGENCYSOURCE S/ RESERVOIRS WITH VIRULENT AGENT ARE IN ABUNDANCETRANSMISSION IS HIGHPOPULATION WITH PLENTY OF SUSCEPTIBILESMethods of control :-NotificationIsolationQuarantineSurveillanceChemotherapyProphylaxis
32 DISEASE ELIMINATION NEAR ERADICATION STAGE INTERMEDIARY BETWEEN CONTROL AND ERADICATION STATUSLESS PUBLIC HEALTH PROBLEMBASED MAINLY ON SURVEILLANCE ACTIVITIESLESS NUMBER OF SOURCESAGENT IS STLL PRESENT BUT LESS VIRULENTTRANSMISSION IS PRESENT BUT AT LOW EBBSUSCEPTIBLES STILL PRESENT
33 ERADICATION RADICLE MEANS MAIN ROOT OF A PLANT ERADICATION MEANS REMOVING ALONG WITH THE MAIN ROOT i.e. IN ENTIRETYALL OR NONE FORMULA
34 DISEASE ERADICATION TO ERADICATE THE DISEASE ONE MUST: AGEENT IN RESERVOIROR SOURCEMODE OF TRANSMISSIONSUSCEPTIBLEPOPULATIONTO ERADICATE THE DISEASE ONE MUST:- ELIMINATE THE RESERVOIR/SOURCE OF THE AGENT- CUT OFF THE TRANSMISSION- MAKE THE PEOPLE IMMUNE TO THAT DISEASEAGENT PERISHED IN POPULATIONNO TRANSMISSIONNO SUSCEPTIBLES IN POPULATIONS . (IMMUNE POPULATIONS)HENCE NO DISEASE
35 REFERENCESLast JM: Public Health and Human Ecology, 2nd Edition. Stamford, CT: Appleton & Lange, 1998; pp 8-9.Thucydides: The Peloponnesian War. Translated by Rex Warner. Harmondsworth: Penguin Classics, 1954; Book 2, Chapter 5, ppFor a good introduction, see for example McNeill W: Plagues and Peoples. New York: Doubleday, 1976Zinsser H, in Rats, Lice and History (Boston: Little, Brown & Co, 1935) gave a sparkling account of the influence of typhus on the outcome of wars. Diamond J, in Guns, Germs and Steel (New York: Norton, 1997) strains credibility with a grand theory based on flimsy factual foundationsSemmelweiss IP: Die Aetiologie, der Begriff und die Prophylaxis des Kindbettfiebers. Pest, Wien und Leipzig: CA Hartleben, 1861