Epidemiology Mch 101

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  • 8/6/2019 Epidemiology Mch 101



    ANA LIZA CARPIO-JABONERO, MD, MPHLocal Health Support Division

    Department of Health-Center for Health DevelopmentDavao Region

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    Learning Objectives

    1. Describe the origins of epidemiology2 . Define epidemiology

    3 . Describe the scope of epidemiology4 . Discuss the contribution of epidemiology in

    the control of diseases

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    Learning Objective

    5 . Define health and disease6 . Identify the stages of disease

    7 . Compute the measures of disease frequencygiven a set of data

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    Definition of Epidemiology

    Historical contextDefinition and scope of epidemiology

    Achievements in epidemiology

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    Historical Context:

    Origins1. Hippocrates in 400 BC in his On Airs, Waters and Place the

    role of the environment in health and disease occurrence .

    2 . John Graunt, in 1 662, published Natural and PoliticalObservations Made Upon the Bills of Mortality which recordedcharacteristics of birth and death data, including seasonalvariations, infant mortality, excess of male over female deaths,and other findings . He was the first to employ quantitativemethods in describing population vital statistics .

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    Historical Context:

    Origins3. John Snow investigated a cholera epidemic in mid- 19 th century inLondon . His work featured various techniques in epidemiologicinquiry such as a spot map of cases, tabulations of cases anddeaths, development and testing of hypotheses that contaminatedwater may be associated with cholera outbreaks .

    Table . Deaths from cholera in districts of London supplied by two water companies,8 July to 26 Aug 1 854

    (Source : Snow, 1 855)

    Water supplycompany

    Population1 851

    No . of deaths fromcholera

    Cholera death rate per 1 000 population


    1 67,6 5419 ,1 33

    8441 8

    5 .00 .9

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    Historical Context:

    Origins4.K och, in late 1 800s, espoused the concept thatdiseases are caused by living organisms and madepossible more refined classification of disease by

    specific causal organisms through his postulates for disease causation .

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    Th e h istory of epidemiologic met h odology is largely t h e h istory of t h e development of five ideas:

    a . Human disease is related to the environment in which we live;b. Counting of natural phenomena may even be more instructive

    than just observing them;c. natural experiments can be utilized to investigate disease

    etiology;d. Natural experiments occur more frequently than we think and

    reflect the tremendous heterogeneity of human experience;e . true experiments may be conducted in human populations in

    some circumstances

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    Th e epidemiological approac h of comparing rates of diseases in subgroups of th e h uman population became increasing used in t h e late 19 th and early 20 th


    T he main applications were to communicable diseases .

    T his method proved to be a powerful tool for showing associationsbetween environmental conditions or agents and specific

    diseases .

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    Historical Context:

    Modern epidemiology 5. Framingham Heart Study began in 19 49 for its pioneering

    investigations of risk factors for coronary heart disease .

    6 . After WW II, in 19 50s, Doll, Hill and others studied therelationship between cigarette smoking and lung cancer .

    7 . A long-term follow-up of British doctors indicated a strongassociation between smoking habits and the development of lung

    cancer .

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    Historical Context:

    Modern Epidemiology For many diseases, a number of factors contributed to causation .

    Some factors were essential for the development of a disease- and some just increased the risk of developing it .

    New epidemiological methods were required to analyse theserelationships .

    T oday, communicable disease epidemiology remains of vital importance in

    developing countries where malaria, schistosomiasis, leprosy,poliomyelitis and other diseases remain common .

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    Definition of Epidemiology

    Etymology originates from the three Greekwords- Prefix : epi (on, upon, befall ) +- Root : demos (people, population, man ) +- Suffix: logy (study of )

    Literal translation --- that which befalls man(e .g. , epidemics )

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    Definitions of Epidemiology

    1. It is the study of the distribution and determinantsof health-related states or events in specifiedpopulations, and the application of this study tocontrol of health problems . (Last, 19 88 )

    2. It is the study of the distribution and determinantsof disease frequency in human populations . (MacMahon and T richopoulos, 199 6)

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    Definitions of Epidemiology

    3. Epidemiology is an investigative method used to detect thecause or source of diseases, disorders, syndromes, conditionsor perils that cause pain, injury, illness, disability or death inhuman populations or groups . (T imreck, 199 4)

    4. Epidemiology is a discipline that describes, quantifies, andpostulates causal mechanisms for health phenomena in thepopulation . (Frils and Sellers, 199 6)

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    A natomy of t h e Definition

    1. Population of interest are human populations .2. Describes distribution of health and disease (by person, place

    and time variables ).3. Identifies determinants of health and disease (risk factors,

    causes )4. Health and disease (injury, illness disability or death )

    This emp hasiz e s that ep id em i olog ists a re concerne d no t only withd e ath, i llne ss a nd disabi l it y , b u t a l s o with more po sitiv e he a l th

    stat e s a nd with th e me a ns t o i mpro v e he a l th.

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    Scope of Epidemiology

    Scope : human populationP opul ati on d ef i ne d i n geogr a phi c a l or o ther t erm s e .g . a s pec i f i c group of hos pita l pati en ts or f a c t ory w orker s c a n be a un it of st ud y .

    M ost common popul ati on: i n a g iv en a re a or coun t ry at a g iv en ti me basis for d ef i n i ng s ubgroup s with re s pec t t o s ex , a ge

    group , e thn i c it y , e t c .

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    Herd immunity

    A vaccine provides herd immunity if it not only protects theimmunized individual, but also prevents that person fromtransmitting the disease to others, causing decline in prevalenceof the organism in the population .

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    Uses of Epidemiology

    1. Elucidate disease etiology- Ma y a l s o id en ti fy the d e t erm i na n ts of ou t come s of i llne ss..

    leadi ng t o id en ti f i c ati on of pre v en tiv e me thods.

    (E pid em i ology as a basi c me di c a l s c i ence with go a l of i mpro vi ng he a l th)- O ther ou t come s of i n t ere st --- bi olog i c proce ss e s l i ke gro wth,mul ti ple pregn a ncy , i n t ell i gence , a nd fer ti l it y

    Genetic factorsCausation Good health Ill health

    Environmental factors(including lifestyle )

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    Uses of Epidemiology

    2. Explain local disease patterns- B y uti l izi ng what is a lread y kno w n ab ou t th e e ti ology of a pa r ti cul a r he a l th pro blem , ep id em i olog ist ma y be ab le t o expl ai n a nd d e a l , e .g .with a pa r ti cul a r ou tbre a k , a nd formul at e pre v en tiv e me as ure ss uitab le t o a s pec i f i c commun it y .

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    Uses of Epidemiology

    3 . Describe the natural history of disease- T o id en ti fy f a c t or s rel at e d t o the cour s e of the dis e as e once the dis e as e is e stab l ish e d;

    - I t is us eful t o kno w h ow th e d ur ati on of a dis e as e a nd th e pro babi l it y of va r i ou s ou t come s ( e .g ., reco v ery , d e ath, compl i c ati on s) va ry by a ge , gen d er , geogr a phy , e t c .

    DeathNat ur a l hist ory Good health Subclinical Clinical

    changes diseaseRecovery

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    Uses of Epidemiology

    4 . Provide guidance in the administration andevaluation of health services .- Esti mati on of num ber of hos pita l be ds requ i re d for pati en ts withs pec i f i c dis e as e s ( e .g ., men ta l i llne ss) or for a g iv en s egmen ts of the popul ati on ( e .g ., prem at urely born i nf a n ts, disab led el d erly )wi ll requ i re kno w led ge of the frequency a nd nat ur a l hist ory of pa r ti cul a r dis e as e s or of a ll dis e as e s i n the a ffec t e d s egmen ts of the popul ati on .

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    Uses of Epidemiology

    4 . Provide guidance in the administration andevaluation of health services .- The pl a nn i ng of eff i c i en t re s e a rc h (dia gno sti c , th er a peu ti c , or pre v en tiv e ) wi ll requ i re kno w led ge of how ma ny c as e s of a pa r ti cul a r dis e as e a re l i kely t o be foun d i n a g iv en popul ati on d ur i ng a g iv en per i od.

    - K no w led ge of the rel ativ e frequency of dis e as e i n popul ati on

    s ubgroup s is us eful i f it en ab les i nt er v en ti on progr a ms t o ta rge t th e s e popul ati on s e .g .,s creen i ng progr a ms.

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    Uses of Epidemiology

    T reatment/medical care

    Evaluation of Good health Ill healthIntervention

    Health promotionPreventive measuresPublic health services

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    A ch ievements in Epidemiology

    1. Smallpox1 79 0s : cowpox infection conferred protection against smallpox virus(only after 200 years were benefits of the discovery applied andaccepted )19 67 : 1 0-year eradication program of WHO ( 1 0-1 5M new cases; 2Mdeaths annually in 3 1 countries )19 76 : 2 countries19 77 : last naturally occurring smallpox

    US$ 200M outlay estimated to result in savings of US$ 1 500M ayear .Factors for success : universal political commitment, a definite goal, aprecise timetable, well-trained staff and a flexible strategy . And aneffective heat-stable vaccine .

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    A ch ievements in Epidemiology

    2 . Methylmercury poisoning19 50: Mercury released with water discharged from a factory in Minamata, Japan, into asmall baysevere poisoning in people who ate fish contaminated with methylmercury .


    case DDx as infectious meningitis1 21 patients residents close to Minamata Bay; main occupation fishing .People visiting affected families who ate little fish did not suffer disease .Conclusion : something in the fish had poisoned the patients; not communicable or genetically determined .

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    A ch ievements in Epidemiology

    3 . Rheumatic fever (RF ) and rheumatic heartdisease (RHD )

    - Associated with poverty, poor housing, overcrowding : factors favoring spread of streptococcal UR T Is .

    - In developed countries, decline of RF started on 20 th century, beforeintroduction of sulfonamides and penicillin .

    - In developing countries, among socially and economically disadvantagedgroups, RHD is one of the most common forms of heart disease .

    - Epidemiology : understanding RF and RHDdevelopment of methods for prevention of RHD

    role of social and economic contributing factors for outbreaksof RF and spread of strep throat infxn

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    A ch ievements in Epidemiology

    4 . Iodine deficiency diseases- 1 6th century : Goiter and cretinism first described in detail

    - 191 5: endemic goiter named as easiest to prevent;

    - 19 89 , Hetzel : use of iodized salt for goiter control proposed in Switzerland- 199 0s : large-scale trials in Akron, Ohio, USA, on 500 girls, 11 -1 8 yo .- Epidemiology : identification and solving iodine-deficiency problems

    effective preventive measuresmethods of monitoring iodization programmes

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    A ch ievements in Epidemiology

    5 . High blood pressure- in both developed and developing countries;- 20% of people aged 3 5-64 years in USA and parts of China- Epidemiology : defined extent of the problem

    established the natural history of the condition and healthconsequences of untreated HPN

    demonstrated the value of treatmenthelped determine most appropriate BP level at which

    treatment should begin

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    A ch ievements in Epidemiology

    6 . Smoking, asbestos and lung cancer - 19 30s : dramatic increase in occurrence of lung cancer in industrializedcountries- 19 50: first epidemiological studies linking lung cancer and smoking

    - Main cause of increasing lung cancer : tobacco smoking- Other causes : asbestos dust and urban air pollution . - Smoking and asbestos interact, creating high lung Ca rates for workers whoboth smoke and are exposed to asbestos dust .Epidemiology : provide quantitative measurements of the contribution to

    disease causation of different environmental factors .

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    A ch ievements in Epidemiology

    7 . Hip fractures- Epidemiological research on injuries, ie hip fractures due to fall, involvescollaboration between scientists of epidemiology and in the social andenvironmental health fields .

    - implication s for the health service needs of aging population .- Epidemiology : vital in examining both modifiable and non-modifiable factorsto reduce the burden of fractures .

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    A ch ievements in Epidemiology

    8 . AIDS- 19 81 : first identified as a distinct disease entity in USA- 199 2 April: 484, 1 48 cases have been reported (USA-4 5%, Europe- 1 3%,

    Africa-30%, Asia and other areas- 1 2% )- T rue extent of the cases is likely to be much higher than reported .

    - 50% of people with HIV infection likely to develop AIDS within the years .- Of those with AIDS, more than 50% die within 1 8 months of diagnosis .- In USA, AIDS is already a more important cause of premature death thanCOPD and DM .- Epidemiology : identification of epidemic

    determination of pattern of AIDS spreadidentification of risk factorsevaluation of interventions (treatment, prevention, control )

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    Measuring h ealth and disease

    Definitions of health and diseaseMeasures of disease frequency

    Use of available information

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    Definition of Healt h and Disease

    WHO, 19 84 : health is a state of complete physical, mental, and social well-beingand not merely the absence of disease or infirmity

    World Health Assembly, 19 77 :- main target of Member States of WHO : By year 2000 all people attaina level of health permitting them to lead socially and economicallyproductive lives .

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    Definition of Healt h and Disease

    Epidemiologists :

    health states defined as disease present or disease absentT he development of criteria to establish the presence of a diseaserequires definition of normality and abnormality . (difficult)

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    Stages of Disease

    T he development and expression of a disease occur over time andcan be divided into 3 stages :

    1. Predisease stage- (before the pathologic process begins )- early intervention may prevent exposure to the agent of disease

    (e .g. ,lead, trans-fatty acids, or microbes ) preventing the diseaseprocess from starting : PRIMARY PREVEN T ION

    2. Latent stage- (when disease process has begun, but is still asymptomatic )

    - screening and appropriate treatment may prevent progression tosymptomatic disease : SECONDARY PREVEN T ION

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    Stages of Disease

    3. Symptomatic stage- (when disease manifestations are evident )- intervention may slow, arrest, or reverse the progression of

    disease : T ERT IARY PREVEN T ION

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    Measures of Disease Frequency

    Based on fundamental concepts of pre va lence and i nc id enceNote : calculation of measures of disease frequency depends oncorrect estimates of the people under consideration (potentiallysusceptible to the disease studied ): POPULA T ION AT RIS K

    Population at risk can be defined on basis of d emogr a phi c or en vi ronmen ta l factors :

    e .g . , occupational injuries = workforcebrucellosis = people handling animals (farms and

    slaughterhouses )

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    Measures of Disease Frequency

    Prevalence and incidenceT he pre va lence of a disease is the number of cases in a given

    population at a specified point in time .

    T he i nc id ence of a disease is the number of new cases arising in agiven period in a specified population .

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    Measures of Disease Frequency

    T hese are fundamentally different ways of measuring occurrence,and the relation between prevalence and incidence variesbetween diseases .

    High prevalence and low incidence : DiabetesLow prevalence and high incidence : common colds

    (C ol ds occur more frequen t ly tha n diab e t e s b ut l ast only a sh or t ti me ,O nce con t r a c t e d, Diab e t e s is perm a nen t.)

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    Measures of Disease Frequency

    Prevalence and Incidence are more useful if convertedinto rates .

    A r at e is calculated by dividing the number of cases by the corresponding number of people in the population at risk, and isexpressed as c as e s per 10 people .

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    Measures of Disease Frequency:Prevalence rate

    T he prevalence rate ( P ) for a disease is calculated as :Number of people with the disease or conditionat a specified time

    P = ______________________________________ (x 1 0 )

    Number of people in the population at riskat the specified time

    Data on the population at risk are not always available; may use total population as anapproximation .

    P is often expressed as cases per 1 000 or per 1 00 population . In this case,P has to be multiplied by the appropriate factor 1 0 .

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    Measures of Disease Frequency:Prevalence rate

    point prevalence rate = if the data have been collected for one point in time .

    period prevalence rate = the total number of persons knownto have had a disease or attribute at any time during a specifiedperiod, divided by the population at risk of having the disease or attribute midway through the period .

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    Measures of Disease Frequency:Prevalence rate

    Example :

    In a large industrial concern employing 1 0,000 people on January 1 ,2004, 50people have diabetes . An additional 1 00 cases of diabetes were diagnosedbetween January 1 ,2004 and January 1 ,200 5 . During the year, no employeesmoved out of the company due to retrenchment or retirement; neither were newemployees hired . T he prevalence of diabetes as of January 1 ,2004 is :

    P = 50 x 1 000 = 5 cases/ 1 000 employees

    1 0,000

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    Measures of Disease Frequency:

    Factors influencing observed prevalence rate:

    Increased by : Decreased by :Longer duration of the disease Shorter duration of diseaseProlongation of life of patients High case-fatality rate from disease

    without cure Decrease new cases (decrease incidence )Increase in new cases In-migration of healthy people(increase in incidence ) Out-migration of cases

    In-migration of cases Improved cure rate of casesOut-migration of healthy peopleIn-migration of susceptible peopleImproved diagnostic facilities

    (better reporting )

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    Measures of Disease Frequency:Prevalence rate: Uses

    1. Assess the need for health care and the planning of healthservices/project medical case needs

    2. Measure the occurrence of conditions with gradual onset of disease (e .g . , maturity-onset DM, RA )

    3. Assess the PH impact of a disease

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    Measures of Disease Frequency:I ncidence rate

    Numerator : number of new events that occur in a defined periodDenominator : population at risk of experiencing the event during this


    person-time incidence rate- most accurate way of calculating Incidence rate (Last, 19 88 )- Each person in the study population contributes one person-year

    to the denominator for each year of observation before disease

    develops or the person is lost to follow-up.

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    Measures of Disease Frequency:I ncidence rate

    Number of people who get a diseasein a specified period

    I = ______________________________ (x 1 0 )Sum of the length of time during which

    each person in the population is at risk

    T he numerator strictly refers only to first events of disease .T he units of I must always include a dimension of time (day, month, year, etc )

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    ANA LIZA CARPIO-JABONERO, MD, MPHLocal Health Support DivisionDepartment of Health-Center for Health DevelopmentDavao Region

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    Session Objectives

    1. Identify sources of epidemiologic data


    Describe the integrity and comparability of data, and identify gaps in data sources

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    Epi Data

    1. Disease status2. Exposure status (intrinsic and extrinsic factors )3. Others

    - vital event- socio-demographic/ cultural data- health resources- services

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    T ypes of data

    1. Primary data2 . Secondary data

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    Primary data :1. Observation (direct measurement )2 . Q uery (interview or questionnaire )

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    Secondary data1. Vital records (birth/death certificates )2. Reportable disease statistics

    3. Disease Registries4. Morbidity Surveys5 . Screening Surveys6. Patient Records (hospitals, private clinics )

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    1. Identify the epi data that can be derived from eachof the following sources

    2. Give your comment on the quality of data

    (completeness/accuracy ) that can be obtainedfrom each source

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    Data Sources Key Info Completeness & Accuracy

    1. Vital stats

    1.1 Death certificate

    1 2 Birth certificate

    2. Reportable Disease Stats

    3. Disease Registries

    4. Morbidity Surveys

    5 . Screening Surveys

    6. Patient records (hospital/MDpractice )

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    Q uality and Utility of Data

    1. Nature of data-- routinely collected (registration system ), survey data,hospital or clinic cases, MDs records

    2. Availability-- ad hoc (prn )? Periodic ? (weekly, annual, etc )

    3. Completeness of population coverage (thoroughness )-- Are all cases identified ?

    4. Value and Limitation

    -- Utility of data, accuracy of information

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    1. Vital R ecords

    1.1 Death Certificate (Mortality Statistics )

    Information Completeness/accuracy1. Fact of death Satisfactory

    (d e aths unl i kely t o go unrecor d e d)

    2. Cause of death Not satisfactory

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    1. Vital R ecords

    1.1 Death Certificate : Issues/Problems

    1. Dia gno sti c i na ccur a cy

    2 . U navai l abi l it y of c a us e of d e ath stat emen t

    3. Lack of sta nda r dizati on of dia gno sti c cr it er ia

    ( What con stit u t e s a c a us e of d e ath? a ccep tab lec a us e of d e ath?)

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    1. Vital R ecords

    1.1 Death Certificate : Causes of Problems

    1. Medically unattended deaths (verbal autopsy )2. Lack of training of certifying MDs on cause of death

    certification/ access to guidelines3. Attitude of MDs

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    R esearch Findings: Completeness and Acceptability of cause of death statement in death certificates

    19 % completely filled upOf the 19 %, only 1 2 were filled up in an acceptable manner

    Among the items, underlying cause was the least filled up (28% ) (Immediate cause= 9 2%, Antecedent cause= 57% )

    5% underlying cause are unacceptable entries(Cardiac arrest, respiratory arrest, CR arrest, heart failure, DOA,Shock )

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    1. Vital R ecords

    1. 2 Birth Certificate/fetal death

    Information Completeness/accuracy

    1. Fact of birth Satisfactory(bi r ths unl i kely t o be recor d e d)

    2. Condition of child at birth(weight, abnormality, etc )


    3. Condition of mother duringpregnancy/delivery

    Not satisfactory( rec a ll )

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    2. R eportable Disease Statistics (N otifiable)

    MDs/health facilities legally required to report cases of certain diseases to health authorities

    System of reporting is in placeIssues/Problems :

    Not all will seek medical attention; asymptomaticFailure of MDs to fill out the required reporting formsMDs concern over confidentiality of information

    WHO : reluctance to admit occurrence of certain diseases

    --Unsatisfactory source (incomplete population coverage )

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    Notifiable Diseases (2001, FH SIS)

    Anthrax Neonatal T etanusCholera Non-neonatal tetanusDiphtheria Meningococcal infectionViral enceph Paralytic shellfish poisoning

    Leprosy RabiesLeptospirosis T yphoid and paratyphoid fever Malaria PertussisMeasles

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    Notifiable Diseases ( Syndromes )

    Acute Flaccid Paralysis Acute Hemorrhagic Syndrome Acute Lower Respiratory T ract Infection and Pneumonia Acute watery Diarrhea Acute Bloody DiarrheaFood PoisoningChemical Poisoning

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    3. R egistries

    -- centralized database for collection of information about a disease(cancer, trauma, etc )

    -- newly recognized cases are entered and maintained in a file untilrecovery, death, or migration

    -- Source of data for :duration of illnessoutcome of illness (Case fatality )incidence and prevalencenatural history of disease

    -- Satisfactory source of data only for some diseases

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    4. Morbidity Surveys

    Sample population (representative sample )National Demographic and Health Survey (NSO )

    --every 5 yearsNational Nutrition Survey (FNRI )

    -- every year National weighing,Operation T imbang (DOH )

    --on-going ( 1 5 years )Prevalence Surveys (periodic )-T B, Disability, S T D

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    5. Screening Surveys

    Sample population (non-representative sample )

    Neighborhood screening clinics

    Health fare, civic groups

    -- not satisfactory source

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    6. Hospital Data

    In-patient and out-patient recordsDoes not represent a specific populationT ype of information is not standardized

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    R esearch Findings: Comparison of data from multiple sources

    Agreement between medical record and interview isvariableExcellent agreement (inherent features of patients

    clinical condition surgical procedures, familyhistory of cancer )Poor agreement (pharma use )

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    A gencies concerned wit h collection,management, and publication of h ealth data:1. DOH

    - Phil . Morbidity and Mortality Report (quarterly )- Field Health Service Information System (FHSIS )

    a . stat indicators of health programs,DOHb. vital stats, by province, city, region

    - Philippine Health Statistics (including notifiable diseases )2. NSO

    - Vital events (births, deaths, marriages )- National Demographic Survey (every 5 years,2003 )

    --demographic, maternal and child health stats

    3. FNRI- National Nutrition Survey

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    Use of A vailable Information

    Epidemiology rely on a variety of sources for obtaining data to analyzehealth-related rates and risks . Data can be discussed in terms of :

    1. Denom i nat or data : d ef i ne the popul ati on at r isk ; C en s us

    statisti c s2 . N umer at or data : d ef i ne the e v en ts/ con diti on s of concern ;

    statisti c s from he a l th, dis e as e , bi r th,a nd d e ath reg ist r i e s a nd s ur v ey s

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    Use of A vailable Data: A . Mortality

    Death Certificate :fact and cause of death, age, sex, DOB, place of residenceUseful only if data are complete and accurateNot in all countries : no resources for routine death registers, not

    reported due to cultural or religious reasons .

    I nt ern ati on a l C l assi f i c ati on of Dis e as e s (WHO,199 2b )revised at regular intervalsused for coding causes of deaths;

    account of the emergence of new diseases and changes incriteria for established diseases

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    Use of A vailable Data:MO R T A LI T Y

    Number of deaths in a specified periodCrude mortality rate = ____________________________________ (x 1 0 )

    Average total population during that period

    Disadvantages :No account of fact that the chance of dying varies according to age, sex, race,socioeconomic class, and other factors .Not appropriate for comparing different time periods or geographical areas .

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    Use of A vailable Data:Mortality

    Age-specific and sex-specific death rate :

    T otal number of deaths occurring in a specific age- and sex-groupOf the population in a defined area during a specified period

    _____________________________________________________ (x 1 0 )

    Estimated total population of the same age- and sex-group of thePopulation in the same area during the same period

    Proportionate mortality rate : (ratio )Number of deaths from a given cause/ 1 00 (or 1 000 ) total deaths in the same period

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    Use of A vailable Data:Mortality before and just after birt h

    Infant Mortality RateNumber of deaths in a year of children less than 1 year of age

    = _________________________________________________ x 1 000Number of live births in the same year

    IMR as an indicator of the level of health in a community :based on the assumption that IMR is particularly sensitive tosocioeconomic changes, and to health-care interventions .

    High IMR should alert health professionals to the need for investigationand preventive action on a broad front .

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    Use of A vailable Data:Mortality before and just after birt h

    Other measures of mortality in earlychildhood :

    F e ta l d e ath r at e

    S ti ll bi r th or l at e fe ta l d e ath r at eP er i nata l mor ta l it y r at eN eon ata l mor ta l it y r at eP ost nata l mor ta l it y r at e

    Precise guidelines on the definition is found inICD.

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    Use of A vailable Data:Mortality before and just after birt h

    Child Mortality Rate :- Based on deaths of children aged 1 -4 years .- Common in this age group : accidental injuries,

    malnutrition and infectious diseases.

    Household survey questions used, if without accuratedeath registers :

    During the last 2 years,have any children died who were aged 5years or

    less ? How many months ago did the death occur ? How many months of age was the child at death ? Was the child a boy or a girl ?

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    Use of A vailable Data:

    Maternal mortality rate :Maternal pregnancy-related deaths in one year

    = ______________________________________ (x 1 0 )T otal births in same year

    Lif e expectancy: Another frequently used summary measure of the health status of a population .

    Defined as : the av er a ge num ber of ye a r s a n i ndivid ua l of a g iv en a ge is expec t e d t o l iv e i f curren t mor ta l it y r at e s con ti nue .

    Lif e expectancy (years) at selected ages f or f our countr ies

    Age Mauritius Bulgaria USA JapanBirth45 years65 years

    65 .025 .311. 7

    68 .327 .31 2.6

    71. 630 .41 5 .0

    75 .832 .91 6 .2

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    Use of A vailable Data:MO R B IDI T Y

    Morbidity: -the frequency of illness-useful for investigating diseases with low case-fatality e .g. , RA, chicken

    pox, mumps-helpful in clarifying the reasons for particular trends in mortality : changesin death rates could be due to changes in morbidity rates .

    B ec a us e popul ati on a ge st ruc t ure s c ha nge with ti me , ti me - t ren d a na ly sis sh oul d b e bas e d on a ge -sta nda r diz e d mor bidit y a nd mor ta l it y r at e s.

    f A

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    Use of A vailable Data:MO R B IDI T Y

    T he morbidity data are collected to meet legal requirements e .g. , notifiablediseases : quarantinable diseases (cholera ), AIDS

    N oti f i c ati on = d epen ds on pati en ts s eek i ng me di c a l advi ce , th e correc t dia gno sis b e i ng mad e , a nd th e no ti f i c ati on s b e i ng for wa r d e d t o the publ i c he a l th a uthor iti e s. Ma ny c as e s ma y ne v er be no ti f i e d.

    F or dis e as e s of maj or publ i c he a l th i mpor ta nce , no ti f i c ati on s a re coll at e d by the WH O , a nd publ ish e d i n the W eekly ep id em i olog i c a l recor d.

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    U f A il bl D

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    Use of A vailable Data:MO R B IDI T Y

    Factors influencing Hospital Admission Rates :1. Morbidity of the population2 . Availability of beds3 . Admission policies4 . Social factors

    H osp ital adm iss ion rates f or asthma per 100,000 by age (Auckland,NZ)

    Age group(years )

    19 60 19 70 19 80

    0 1 41 5 4445 - 64

    40 1 60 4 5045 11 5 20070 11 5 220

    U f A il bl D

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    Use of A vailable Data:MO R B IDI T Y

    T he morbidity data are collected to meet legal requirements e .g. , notifiablediseases : quarantinable diseases (cholera ), AIDS

    N oti f i c ati on = d epen ds on pati en ts s eek i ng me di c a l advi ce , th e correc t dia gno sis b e i ng mad e , a nd th e no ti f i c ati on s b e i ng for wa r d e d t o the publ i c he a l th a uthor iti e s. Ma ny c as e s ma y ne v er be no ti f i e d.

    F or dis e as e s of maj or publ i c he a l th i mpor ta nce , no ti f i c ati on s a re coll at e d by the WH O , a nd publ ish e d i n the W eekly ep id em i olog i c a l recor d.

    U f A il bl D

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    Use of A vailable Data:DI S AB ILI T Y

    Measurements of occurrence, also of persistence of the consequences of disease, WHO, 19 80b :

    1. Impa irment : any loss or abnormality of psychological, physiological or anatomicalstructure or function .

    2. Disab

    ility : any restriction or lack (resulting froman impairment ) of ability to perform an activity in

    the manner or within the range considered normalfor a human being .

    U f A il bl D t

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    Use of A vailable Data:DI S AB ILI T Y

    3 . H and icap : a disadvantage for a given individual, resulting froman impairment or a disability, that limits or prevents the fulfillmentof a role that is normal (depending on age, sex, and social andcultural factors ) for that individual .

    M e as uremen t of the pre va lence of disabi l it y pre s en ts pro blem s a l s o, a nd isa ffec t e d b y ex t r a neou s s oc ia l f a c t or s.

    I t is i mpor ta nt i n s oc i e ti e s with i ncre asi ng num ber of a ge d people .

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    Session Objectives

    1. Define cause of a disease2. Determine the types of factors of disease3. Describe the different risk factors of disease using the BEINGS

    model4. Discuss how to establish the cause of disease in terms of

    temporal relationship, plausibility, consistency, strength, dose-response relationship, reversibility and study design

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    Th f

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    Th e concept of cause

    A c a us e of a dis e as e is a n e v en t, con diti on , c ha r a c t er isti c or acom bi nati on of the s e f a c t or s, whi c h pl a y s a n i mpor ta n t role i n pro d uc i ng the dis e as e .

    Logically, a cause must precede a disease . A cause is termed sufficient when it inevitably produces or initiates a

    disease . A cause is termed necessary if a disease cannot develop in its

    absence .

    Th f

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    Th e concept of cause

    A sufficient cause is not usually a single factor; comprises severalcomponents .

    It is not necessary to identify all the components of a sufficientcause before effective prevention can take place . T he removal of one component may interfere with the action of the others, andthus prevent the disease .

    E x a mple: c i g a re tt e s mok i ng 1 componen t of the s uff i c i en t c a us e of lung c a ncer . Smok i ng is no t s uff i c i en t i n itself t o pro d uce the

    dis e as e . H ow e v er , th e ce ssati on of s mok i ng re d uce s th e num ber of c as e s of lung c a ncer i n a popul ati on e v en i f the o ther componen t c a us e s a re no t a l t ere d.

    Th f

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    Th e concept of cause

    Each sufficient cause has a necessary cause as a component .Example 1 : Outbreak of foodborne infection :

    - chicken salad and creamy dessert-both s uff i c i en t c a us e s of salmonella diarrhea

    - occurrence of salmonella is a necessary cause of disease .

    Example 2 : T B: tubercle bacillus as the necessary cause .Susceptible host : Infection T B

    Genetic factorsMalnutritionCrowded housingPoverty Exposure to bacteria T issue invasion

    Th t f di

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    Th e concept of disease

    Kochs postulate : rules for determining whether a specificliving organism causes a particular disease .

    T he organism must be present in every case of the disease;T he organism must be able to be isolated and grown in pureculture;T he organism must, when inoculated into a susceptible animal,cause the specific disease;T he organism must then be recovered from the animal and

    identified .

    A n th r a x - f i r st dis e as e d emon st r at e d t o mee t th e s e rule s; pro v en us eful with s ome o ther i nfec ti ou s dis e as e s.

    F i C i

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    Factors in Causation:

    Four types of factor play a part in the causation of disease . All may be necessary but they are rarely sufficient to cause a

    particular disease or state :

    P re dis po si ng f a c t or s , such as age, sex, previous illness, maycreate a state of susceptibility to a disease agent .E nab l i ng f a c t or s , such as low income, poor nutrition, badhousing, and inadequate medical care, may favor developmentof disease .

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