Epidemiology - Ignou

8/13/2019 Epidemiology - Ignou

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UNIT INTRODUCTION TO

Structure4 0 Objectives4 1 Introduction4 2 Epidemiological Concepts

4.2.1 Epidemiological Trends and Definition4.2.2 Aims of Epidemiology

4 3 Epideiniological Aspects of Disease and Health4.3.1 Epidemiological Models of Causation of Disease4.3.2 Epidemiological Model of Determinants of Health4.3.3 Natural History of Disease4.3.4 Spectrum of Diseasc4.3.5 Ice-berg of Disease4.3.6 Levels of Prevention of Disease

4 4 Epidemiological Methods4.4.1 Descriptive Epidemiology4.4.2 Analytical Epidemiology4.4.3 Experimental Epidemiology

4 5 Epidemics4.5.1 Concepts of Epidemics4 5 2 Investigationof an Epidemics

4.6 Preventive Epidemiology4.6.1 Health Surveys4.6.2 Screening of Disease4 6 3 rSurveillance4.6.4 Monitoring and Evaluation

4.7 Epidenliology ndN~~rsing4 8 Let Us Sum Up4 9 Key Words4 10 Answers to Check Your Progress4 0 OBJECTIVESAfter going through this unit you should be able to:

define the science of epidemiojogy;describe the epidemiological trends and explain the modern concept of

state the aims and scope of epidemiology;discuss epide~niologicalheories of disease causation;discuss epidemiological models of health determinants;definq natural history af disease and discuss its process;


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Principles nd Practice explain levels of prevention of disease ;of Community HealthNursing describe epidemiological methods;define different types of ep idemic and describe investiga tion of epidemics;describe interventions of preventive epidem iology; andidentify the role of a nurse in epidem iological process.

4 1 TRODUCTIONCommunity health is the field concerned with the study of health and diseases inhuman population and its goal is to provide com prehens ive need based hea lth careservices to the entire community to achieve the goal of Heal For All. Th e healthworker, therefore, need to have some basic know ledge and skills which w ill help her1him to identify health need, health problem, the related etiology and plan, implem entand evaluate health care services. The science of epidemiology helps health workersto develop such knowledge and skills.Tn this unit w e shall discuss a bou t, concep ts ofepidemiology, epidemiological concepts of disease causation, epidemio logical m ethods,Epidemics monitoring and evalua tion of role of nurse in epidemiology.

4 2 EPIDEMIOLOGICAL CONCEPTSThe science of epidemiology deals with the study of health related states and eventsoccurring in a population. The origin of this science has been traced t the time ofHippocratres who tried to explain the causative factors of discases. But it flourishedrapidly during the last three decades of the present century and contributedextensively in the field of medicine and comm unity health. As a science and academicfield, epidenliology not only helps in understand ing the health concepts, n atural historyof disease and disease causation, it also helps in planning, implementing and evalua tingeffective and efficient health care services.4 2 1 Epidemiological Trends and DefinitionThe term epidemiology is derived from the term Epidemic . T he literal meaning ofthe term is study among people (Epi among, demos people , logos study). Thefoundation of the epidemiology was laid in the 19 th century when infections andcommunicable diseases like cholera, typhoid, plague etc., were most preva lent in theworld in the form of epidemics and pandemics. During the late 1 9th centu ry and theearly 20th century, the study of frequency, distribution and determinants of infec tionsand communicable diseases and their pe venti on an d control were the primary focci ofepideiniologists. There has been considerable reduction in the morbidity and m ortalityfrom these diseases as a result of epidemio logical studies and improved m ethods ofdiagnosis, prevention and control. However, the threat of communicable d isease i s stillpresent, specially in developing coun tries, because of substandard environm ex~ta lconditions, poor socio-econo~n ic tatus and inadequate resources.It may also be defined as the study of frequency, distribution and determinants ofhealth related states and events and disease in human populations.

1Frequency rates, ratio, normal ranges lIDistribution time, place and person i


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From the above definition and concepts it can be said that it includes three importantelements: - 4- All diseases and health-related diseases - oth communicable andnon-communicable- Populations- Ecological approach.While communicable diseases continue to be serious public health problems, manynew problems have come up in the 2 th century. These problems includecardio-vascular diseases, cancer, diabetes, accidents etc. These problems are takingthe form of epidemic. The focus of epidemiologists is now, not only on communicablediseasQ but also on these new emergent and chronic diseases. In fact, theepidemiologists study all those conditions that affe'ct the health of a population at anygiven time.Thus, several definitions have been given by various authors based on their experiencebackground and chang ing trends which are listed below:1) The epidemiology is that branch of medical science which deals with epidemics(Parkin, 1873)2 Epidemiology is the science of m a s phenomena of infectious diseases (Frost,1927)3 Epidemiology is the study of disease, any disease, as a mass phenomenon(Greenwood, 19344 ~ i d e m i o l o ~ ~s the study of the d istribution and determinants of diseasefrequency in man (MacMohan?19605 Epidemiology is the s tbdy of frequency, distribution and determinants of healthrelated states, events and morbidity patterns in population, and the application ofthis study to control health problems (Last, 1983)From these various definitions it is learnt that modern epidemiology deals with:

tMeasurement of occurrence of health related statesland events iie., health needs,health demands, blood cholesterol level, etc., and measurement of frequency ofdisease, disability or death. The measurements are done in the form of rates,

Introduction to Epidemiology

ratios and propo&on e.g., incidence rate, male - emale ratio, percentage ofchildren with malnutrition etc. Rates, ratios and proportions can help in m kingcomparison of different population d i f f e r e n t time with re'spect to occurrence ofdisease, health related stateslevents.Distribution of disease pattern in a community .by time, place and person. Theepidemiologist examines whether there is increase o r decrease of d isease orhealth related Bvents over time, whether there is high or lower concentration of.disease or health related events in different places; whether the occurrence ismore in m an than in woman and in what particular age and with particular lifestyle etc,,aetiolog ical hypothesis e.g, Smoking of 15-20cigarettes per day over ap&bd of 10-15 yearsais associated with lung cancer in men and womenoccurrence of diarrhea is more frequent in non-breast fed infants than in breastfed infants of low sgcio-economic population , This aspect of epidemiology refersto descriptive epidexnialogy.'Testing of e tiological hypothesis derived from descriptive study of diseases andhealth rela ted events. This'iaspect of epidem iological s&es help in establishingcause and effect relationship dnd it refers to analytical and experimentalepidemiology, = .


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Principles and Practiceof Community H ealthNursing

Planning of health card services based on the studies implementation andevaluation of he lth care services.The uses of epidemiology are:

To study the health history of popylation and their disease trends.To arrive at community. diagnosis.To plan and evaluate health services.TO estimate individuals risk and chance.To define and redefine syndromes.To complete the natural history of disease.To search for causes of health and disease by employing epidemiologicalmethods.

4 2 2 Aims of ~pidemiology . .\Based on the concept of epidemio1ogy;three main aims have been identified byInternational Epidemiological Association:

1 to describe.the occurrence and distribution of disease problems in humanpopulation.2 to identify aetiological factors in the pathogenesis of diseases.3 to provide information on health related states and events for planningimplementation and evaluation of comprehensive health care services to ded with

health problems and promote health and well being of the society s a whole.


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4 3 EPZDEMIOLOGICALASPECTS OF DISEASEAN D Introduction to Epidernioloe

With the progress of civilization from the primitive period to modern time the conceptof disease and health have changed from supra-natural to multifactorial causes andholistic health approach. But these old concepts still preyail among people in the worldwho are under-developed. Therefore, it is important to clarify the concept of healthand disease.4 3 1 Epidemiological Models of Causation of DiseaseBefore the discovery of micro-organisms in 19th century diseases Cvere associatedwi supranatural and spiritual forces. The ge i theory became popular during the19th and early part of 2 th century. According to this. theory there is one singlespecific causative agent to every disease as shown in the model given below. , ]~ x a m ~ l e sre: . .,

Disease agent.. .Man.. .Disease.Tuberculosis due to tuberculosis bacilli, cholera due to cholera vibrio, diphtheria due tomycobacterium diphtheria etc.

But this'theory has mariy limitations. .For example every one exposid to disease agentdid not get the disease say like tuberculosis, only those who were undernourished;susceptible and lived in slum got the disease. This means in addition to specificcausative' agent there are many other factors related to host nd environment whichcontribute to causation of disease as shown in the Fig. 4.1.Epidemiological B ia d

gent Host

I

EnvironmentEpidemiological concept of interaction o Host, Agent and .Environment

Fig 4.1: Epidemiological Methods of Causation of Disease


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and racticeommunity Health This model is known as_Epidemio_~ogicalriad. According to this model disease iscausedhy the interactionofagent, host nd environment which is shown in the modelFig. 4.1. This means the disease will occur only when the host is weak, the agent isstrong nd enters the host through the right channel nd in sufficient amount and whenenvironment conditions facilitate the interaction of host and agent. For example forpulmonary tuberculosis, the organisms must enter through respiratory tract and insufficient amount, the host should not have specific resistance and should have weakgeneral body resistance, poor, d rk and dingy environment is conductive to theprevalence af tuberculosis on patiqnts.This model in ~ ther ords implies that disease will not occur without the optimalinteraction of these three factors and remain in balanced state. This refer to state ofhealth equilibrium and is represented in the following model of Alten Dever(see Fig. 4.2.

Fig 4 2: Ecological Model of Health EquilibriumThis model is applicable to infectious diseases and not to new types of chronic anddegeAerative diseases which are a result of modern civiiization, for example cancer,cardiac diseases, diqbetes, nephroitic syndrome, mental disorders, etc. These diseasescould not be prevent@ and controlledby the traditional methods of isolation, curative,immunizationand environmental sanitation, etc. -

Changes in Stressi i \

Overeating ' lackof physical SmokingexerciseEmotional Disturbances

Hyperlipidaernia , tncreased;hrombotic Changes in walls of arteriesTenrny ,Coronary Occl wsionCoronary IIatherasclerosis I

Myocardial lsekaemia

Myocardial Infarction~ g .3: The Web of Causation for Myocardial Infarction

I


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It has been epidem iologically recognized that these diseases are caused due tocomplex interaction of m ultiple factors related to life style, human behaviour and theenvironmental conditions as shown in model Fig. 4.3. Agent is regarded as an integralpart of total environment.This refers to web of causation as suggested by MacMohan and Pugh. This modelsuggests clusters of cases and combinations of effects related to each other. It alsosuggeits variety of in terven tion e.g., avoidance of smoking, diet control, exercise,regular health check ups, etc., for prevention and controlsf cardio-vascular diseases,cardio-pulmonary diseases, etc.4 3 2 Epideqiological Model of Determinants of Health

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Of late the epidem iologist proposed a model fo r analysis of health of people ratherth n analysis of k se a se amo ng the people. According to this model, health isinfluenced by a v d e t y of factors which are classified as life style, environment,human biology and health and health allied resources as shown in the model Fig. 4.4.These four categories of factors are related to n affect one another and interact witheach other. Epidemiologists try to analyze these factors to study the health status,morbidity and mortality pattern in any community. This model refers to health forcefield model as suggested by Blum.

Health allied resources

EnvironmentHg 4 4: Model of D~terminants f Health

4 3 3 Natural History of DiseaseIn the absence of any intervention (i.e., prevention or treatment) almost all diseasefollow a natura l cou rse of events which refers to natural history of disease . I t startswith the interac tion of agent, host and environment i.e., epidemiological triaa asdiscussed earlier.The disease process in m n depends o n the characteristics of these three factors. Thenatural histo* o disease has'two phases: (i) Prepathogenisis phase and (ii)Pathogenesis phase.Prepathogenisis Phase .p his phase is before the onset of disease in man and it is in the environment. Thedisease agent has yet not entered the host (&an). But the factors that favour its(agents) interaction with the human ho st exist in the environm ent (Fig. 4.5 e.g., poorphysical environm ent, climate condition and prevalence of insects, pests and rodents,etc., unhygienic hab its and hea lth behavior, traditional practices and biological factorsi.e., age, s&, marital status, genetic traits, physiological status, etc., we h e alwaysexfiosed to k e isk to disease but disease process in man starts only when there isinteraction m o n g agent, host and environmental factors as shown in the model~ ~ i d e m i b l o g i c a lriad (Fig. 4.1 and Fig. 4.5 .



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Principles and Practiceof Community HealthNursing

Fig 4 5: Prepathogenisis and Pathogenisis Periods of Natural History

PrepathogenisisPeriodBefore man,is diseasecAgent OSt

Environment

Pathogenesis haseThis phase begins with the entry of the disease agent in the human host. As the agente.g., measles virus enter the body through appropriate channel e.g., in case ofmeasles virus, the respiratory tract, the agent in this case i.e., the visus grow andmultiply and bring in physiological changes in the body. These changes are sub-clinicali.e., clinical signs and symptoms of the disease are absent. The host remainsapparently healthy and arnbulant. After a lapse of some period, which difIer in variousdiseases, the health equilibrium within the body is dislurbed, the signs and symptoms ofdisease begins to appear. This period is called as incubation period. The signs andsymptoms are vague during the first few days (1 to 4 days ) of illness e.g., in measles,running nose, watering of ejres, etc. This period is called as prodromal period and it isearly prepathogenesis phase. But as the disease advances, the signs and symptomsusually become clear cut and clinical diagnosis can be made with ease e.g., skin ashesall over the body in measles. This stage of pathogenesis (disease process) refer toFastegium. Its duration varies from disease to disease and in case of same disease indifferent people depending upon the virulence of causative agent and the susceptibilityof human host. The end results of disease. pwcess may be complete recovely whichrefers to defervescence and convalescence or it may end into some kind of disability1defect, chronic state or death. From this discussion of pathogenesis phase of a diseasewe learn that each disease has a series of stages as shown in the Fig. 4.5.

Period of Pathogeniss .The course of disease n human

Death

4 3 4 Spectrum of Disease

clinicalHorizonEarlyPathogenisis

whenever any disease occurs in the community everyone does not get sick. It is onlysome people who get sick who show clinical signs and symptoms of the disease. Theseverity of the sicbess also varies ranging from mild to severe. These variations aredue to susceptibility of the host, virulence of the agent and the various environmentalfactors which influence the host agent interaction. Many people get the infection butremain sub-clinical i.e.,do not show recognizable signs and sylnptoms but remain ascarriers of infection. They are a source of risk to others and create public healthproblems.The graphic representation of these variations in disease occurrence refer t;o spectryrho f disease which is like a spectrumof sunlight having different shades of colors froinone end to the other. At one end of the spectrum are sub-clinical cases whereas i t theother end ase very serious and fatal cases (see Fig. 4.6 .

Incubationperiod

- astegium

DiscernibleearlyDiseaseDefervescence

Advanceddisease Convalescence Defection


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4.3.5 Ice-berg of Disease Introduction to pidemiologyFrom the spectrum of disease we 1ea1-n that when a disease occurs in a co~nmunitythe physician will be ab le to recognize only clinical cases which is like the floating tipof the ice-berg which is visible on the surface of water. He is not able to recognize alarge number of sub-clinical or presymptomatic and missed, cases which remainhidden like the vast submerged portion of the ice-berg as shown in the Figure.The hidden cases we much more8thanknown cases and they are a source of infectionb e c a ~ ~ s ehey ase casriers of infection. The detection and control of hidden cases is achallenge for health personnel in the field of community health.4.3.6 Levels o Prevention of DiseaseWe are all familiar with a vely popular phrase Prevention is better than cure . It isbecause of the i'act that prevenlion helps to promote and preserve health andminimizes the sulfcrings and distress. It is also economical because preventivemeasures can be followed and practiced by all at the village and ho~ lleevel. It doesnot require sophisticated infrastm cture, equipm enls and material. Above all it is apositive appmach Lo healthful living. Epidem iologically, the concept of prevention isbroad based. According to natural h is to ~y f disease, three levels of prevention havebeen identified. They are: (i) Pri ~n ar y revention, (ii) Secondary Prevention, (iii)Tertiary Prevention.I ) Primary Level of Prevention: It refers to prevenlive measures taken beforethe qccurrence of a disease i.e., during the prepathogenesis phase of disease.Preventive measures during this period of a disease process prevent theoccusrence of disease and promote health. These measures we classified as:

Health Promotion: Health promotive factors include wholesome nutritiousfood, safc environmnent to live, h ea lt h f~ ~ life-style and adequate resources. Allthese aspects ase directly related to socio-economic and cultural status of thefanlily which rnusl be ;mnproved. Much of the morbidity and nlortality due toconz~ nunicable iseases such as typhoid, cholera, dysentery, tuberculosis.Plague, leprosy etc., have been reduced due to these preventive measures.Health protnotive measures are equally applicable to thc prcvention ofchronic and non-communicable diseases such as casdiovasculas, diabetes,accidents, etc.Specific Protection: I refers to actions to protect from a particular diseaseor group of disease, like B.C.G. imnzunization for tuberculosis, D.P.T. fo rdiphtheria, pertusis and tetanus, increase or decrease of specific nutrient indiet'and o r supplelnenting it e.g., iron rich diet and supplementing with irontablets in case of prevention of anaemia.Primary prevention is given m ajor emphasis in health care and it is identifiedwith health education becau se it is considered as the responsibility of theindiv idual, family and coinxnunity.

2 Secondary Level of Prevention: Se co nd ay level of prevention refers tomeasures taken during pathogenesis period to control. the progress of disease inman to sto p or control the spread of disease in the comm unity. Secondarypreventive measures p r e~ en t ' d i s ab i l i t ~r defects, and restore health. It includesearly identification of cases and their contac ts and giving them timely treatment'and follow-up e.g., early diagnosis and treattnent of all cases of tuberculosis andtheir contacts. These actions help in early recovery prevent cavilation andconsolidation of the affected p t of the lungs and a lso preven t further sprgad ofthe tuberculosis in comm unity. Similarly, early diagnosis and treatment of highblood pressure will he lp in the lxevention of possible cardiovascular emergencies.Thus secondary level of prevention reduces prevalence rate of the disease i.e.,'prevents the occurrence o f new cases and controls old cases. 8


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rinciplesand ractice 3 Tertiary Level of Prevention: The purpose of tertiary level prevention is tof ommunity Health limit the disability nd help the individual adjusttopermanentimpairment ndNursing disabilities so as to lead a useful life The measures included are physicald vocational and psychosocial rehabilitation e.g. deep breathing exercise .meditation etc. for efficient lung expansion; guidance nd training to learn newvocation and guidance and counseling for restoration of f mily and socialrelations etc. in case of patients with pulmonary tuberculosis.


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Introduction t Epidemioloj y


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and PracticeCommui~ityHealth 4 4 EPHDENIPOLOGIC Lti The epidemiologist and comtnunity health workers are interested in the study of thehealth status of the population at large, idenlify morbidity and mortality patterns,determine the factors affecting health and disease and utilize this infonllation inplanning to provide need based health care services. Such epidemiological studyrequires systematic collection of health data, its analysis, description of health needsand health problems, identification of factors associated with the probleins and stating

the hypothesis which are: i) Descriptive method, (ii) Analytical method,(iii) Experimental method. Descriptive and analytical methods or studies are alsoknown as observational studies because the investigator does not intervene, he or shemakes an observation of the frequency and distribution of the disease by person, placeand time.4 4 1 Descriptive EpidemiologyDescriptive epidemiology is concerned with the study of frequency and distribution ofdisease and health related events in population in terms of person, place and time. Itspurpose is to provide and overview of the extent of health problems and to give a clueto possible etiological factors involved. This method gives information about who allare affected by a particular disease or health related problems, where the cases occurand when they occur. The data is collected about:1) Perso~ial haracteristics such as age, sex, marital status, occupation, education,income, social class, dietary pattern habits.2) Place distiibution of cases i.e., areas of high concentration, low concentration andspotting of cases in the map.3) Time distribution/trends such as year, season, month, weak, day and hour of onsetof the disease.Such information gives clues to possible associated factors such as age with specificdisease e.g., measles, diphtheria, pertusis, in early childhood, cancer, dietary patternwith obesity; seasonal variation, periodic fluctuation, etc.The data collected re analyzed and presented in terms of percentage, rates andratios. This refers to statistical i~iformation f a problem and are given in the table foryou to learn to coinpute.Thus, descriptive epidemiology provides information for:1) making community diagnosis i.e., describing the nature of diseases or problemsand measuring their extent in terms of incidence/prevalence rate, raC ., mortality

rates, etc., by age, sex, occupation, social class, etc.2) providing ch~eso etiology of disease for further rigorous investigation andconfrontation of the causes.3) planning, organizingmid implementation of health care services to dealwith theseproblems.4 4 2 nalytical EpidemiologyYou have learnt that descriptive studies yield etiological clues for various diseasqswhich helps in making a guess or formulation of hypothesis for further vigorous studyor testing e.g. cigarette smoking 10 to 20) in a day causes lung cancer in 10 to 5percent of smokers after 20 years of exposure . These type of hypothesis are furtherstudied and tested by analytical studies to determine the association of cause with theeffect.Thus, analytical epidemiology goes beyond the descriptive epidemiology. It consists oftwo type of observational studies: i) Case Control Study, and ii)Cohart Study.


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1 Case Control Study In this method a group of people who have been diagnosedas having a particular problem cases) are compared with a group of people whoare similar in charactei.istics to that of cases but they are free from the problemunder study controls). Here the approach used is retrospective i.e., the diseasehas already occurred and the epidemiologist goes back in time. He reviews therecords, interviews the cases and their family members. The data thus collectedabout the suspected factorlfactors is analyzed statistically to determine the extentof its association with the disease. This method, therefore, is called asretrospective method. This approach has helped in identification of causativefactors of m any diseaseslproblems, etc. e.g. Rubella in mothers during earlypregnancy in the cause of congential deformities in children, smoking associatedwith lung cancer, iodine deficiency associated with hyperthyroidism. Theseconclusions are based on repeated cas e control studies. Case control studies areeasy to organize and a re less expensive.

2) Cohart Study A cohart is a specilic group of people, at a certain time, sharingcomm on characteg stics o r experience e.g., people born on the same day or thes a n e year birth cohart), couple married in the same year marriage cohart),class of nursing students experience cohart), people with same occupationsoccupational cohart) etc.oh rt study is prospective in nature because the group under study is free from thedisease but exposed to risk factor. In this m ethod of study the epidemiologist selects acohart i.e., a group of prople say in the sam e age group and who are exposed to acertain risk factor say c igarette smoking study group) and who are not exposed to therisk factors contribi grou p). Both the groups are followed up for several years andobservations are made with referen ce to frequency and distribution of the suspecteddisease in this exam ple lung cancer) over a period of time. The data is statisticallyanalysed and comparisons are done between the incidence am ong smokers andnon-smokers to determine the association of risk factors to the disease.

The prospective study is expensive and time consuming but it has its advantages overretrospective method. This method can help in studying the natural history of disease,estimating incidence rates, risk factor under study to other diseases or problems e.g.,cigarette smoking and h igh blood pressure, cardio-vascular problems etc,4 4 3 Experimental EpidemiologyExperimental studies are similar in approach to cohart studies expect that conditionsare under the ca re f~ ~ lontrol of the investigator. Experimental studies are done toconfirm the cause and effect association of the efficacy of preventive or therapeuticagent or procedure. In these studies the investigator administers and doesinvestigatiod gives treatment to the expe rimental group which is either exposure tocaGsative agent or preventive/therapeutic agent, but not to the control group which issimilar to the ex perimental in all its aspects. H e then observes and analyze theoutc o~n es sing statistical methods and confirm the cause of diseases, and e stablishesthe efficacy or preventive m easures and drugs un der study. Usually these experimentsare done in the lab oratoly animals. But clinical and com munity trials are done todetermine efficacy of preventive or therapeutic laboratory animals. These trials doinvolve medical, ethical and m oral issues.

Intraduction to Epidemiology


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Principles and Practiceof ommunity HealthNursing

n 1994 we read a great deal in the newspaper about plague epidemic in our countryhat is an epidemic?

4 5 1 oncepts of EpidemicsEpidemic is defined as the occurrence of a disease for more than normal expectancyin a qnmunityor region during a specific time period e.g. outbreak of influenza in .


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Delhi in a large number in November-December, food poisoning cases, cholera ins u F tc. There are mainly two types of epidemics, namely: (i) Common sourceepidemic, (ii) Propagated epidemic.I Common Source Epidemic: Most of the time the epidemic occurs due toexposure to an infectious agent from common source, contaminated air, water,food, soil. Examples of epidemic include influenza, hepatitis, cholera, Bhopal Gastragedy. The common source epidemic can be due to:

Single exposure or point source infection: In single exposure or point sourceinfection, the exposure to the agent is brief and simultaneous. The resultantcases develop the problem within one incubation prior to the disease. Theclassical example is for a brief period, i.e. first time and all those who have todevelop the problem, develop within one incubation period because theexposure to infection is only one time. The epidemic is explosive, theepidemic rises and falls rapidly as shown in the Fig. 4.7. there is a clusteringof cases (i.e., cases occur in one particular location usually) within a shortperiod one incubation period.Multiple exposure or continuous exposure: Multiple exposure or continuousexposure is common source epidemic. In this the exposure to infection iscontinuous repeated or intermittent but may not be at the same time or placee.g., epidemic of cholera or infective hepatitis or any other such problem dueto unsafe water supply, milk supply or contaminated well water, epidemic ofSTDs through infected prostitutes. These epidemics are irregular, extendedover a period of time and continued beyond the range of one incubationperiod.

2 Propagated Epidemic: this epidemic results from person to person contact andmostly due to infectious agent. The epidemic flares up gradually depending uponthe herd immunity, opportunity for contact. It tails off gradually bver a long periodof time. Transmission continues as long as susceptible people are there in thecommunity and are exposed to infected people,

4 5 2 nvestigationof an Epidemic


Investigation of epidemic is essential to determine the particular condition or factorswhich are responsible for the outbreak. Often health team at the grass root level ismade responsible to investigate and plan and implement the intervention to control theepidemic. Investigation of epidemic is a systematic process and goes thraugh orderlysteps which are discussed as under:1) Verfication of Diagnosis of Disease: The first step is to diagnose the disease

and is done on the basis of clinical examination of cases. Laboratory examinationis done wherever necessary and applicable.2 Confirmationof the Existence of an Epidemic: This is done on the bases ofthe frequency of the disease. If the frequency is more than normal e xpectancyinthe community then it is considered as an epidemic. Often such comparison is notrequired because there is sudden increase in number of cases within a shortperiod which happens with common source epidemic of cholera, hepatitis, foodpoisoning, etc.3 Defining the Population at Risk: It includes:

Obtaining or preparing a map of the area, The map should show thelandmarks, roads, sections and locations of lldwelling units,Demographic study which includes total population composition. Thisinformation is necessary for calculating epide~niologicalmeasurement e.g.,morbidity and mortality rates and proportions, etc.


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Principles and Practice 4 Identification of all Cases and their Characteristics: This can be d one byof ommunity Health organizing house to house search till th area is free of epidemic and m edicalNursing examination of population at risk. An epidemiological sheet is prepared fo r everycase. It includes basic information on age, sex, occupation, time of the onset ofthe disease, signs and symptoms, information contacts, movem ents, history ofimmunization, information on common source of infection according to the diseaseunder investigation e.g., piuties attended; food eaten sources of w ~ t e r , tc.5 Study of Ecological Factors: It includes investigation of all those eco logical

factors, agent factors and host, actors. This information will help in identificationof the planning of preventive and control measures.6 Data Analysis: The data analysis is the same as in descriptive epidemiology.Description of the cases in terms of person, place and time d istribution. Acomplete list of cases by chronological order is prepared to show the beginning ofthe epidemic. An attempt is made to identify the first case and fo llow itsmovements to trace the source and spread of infection. Spot maps are preparedto find out the geographical distribution of cases. Concentration of casesclustering) will indicate the common source of infection.7) Formulation of H ypothesis: Analysis of data will reveal the possible causes of

epidemic and the inode of the spread of infection. Ultimately the inves tigator isable to formulate the hypothesis.8 Recommendation for Prevention and Control: Based on the informationrevealed about the epidemic, the epidemiologist health worker prepared aprogramme of prevention and control of th epidemic not only the present bu t alsofor its prevention in future.


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4 6 PREVENTIVEEPIDEMIOLOGYPreventive epidemiology is concerned with those m easures at the community levelwhich help in iden tification of population at risk and environmen tal factors leading to illhealth and detec tion of persons with early, mild and symptomatic diseases. Thesemeasures include: Health surveys, Screening, Surveillance and Monitoring.4.6.1 Health SurveysHealth su rveys are investigations to identify health problems in health and disease in acommunity, i.e. occurrence and distribution and the facto rs affecting health anddisease i.e. determinan ts. Health surveys help in making community diagnosis. Thehealth surveys provide comprehensive data about health and sickness status of thewhole comm unity. Genera l health survey is not a regular practice in our country. It hasonly been done once o r twice in our country. Once I 1946 by the Health Survey *andDevelopment Comm ittee headed by Sir Joseph Bhore and again in 1962 by HealthSurvey and Develop ment comm ittee headed by Dr. Mudaliar. Special and specifichealth surveys deal with the inves tigation of selected health problems e.g,, filarialmalaria or tuberculosis etc. W hether gene ral or specific health surveys can becross-sectional or longitudinal. Cross-sectional surveys provide data about theprevalence and distribution of illness and the sta te of health of a community at onepoint in time., Longitudinal ; surveys prov ide v'aluable information about the naturalhistory of diseases, incidence and prev&nce of diseases and the underlying causes,etc., but are difficult to organize and are time consuming etc.4 6 2 Screening of DiseasesScreening of disease is de fined . as The search for unrecognized diseases by m eans ofrapidly applied tests, exam ination or proce dures in an apparently healthy population .Screening helps to detect persons with early mild and symptomatic diseases. Thebasic purpose of screen ing for d isease pro tection is to separate from a large group ofapparently healthy populat ion, those who have high possibility of having the diseaseunder study, so that they m ay undergo further investigation and if diseased, brought totreatment. The screening test are usually very simple, rapid and inexpensive becausethey are meant for large population. T hese a re not diagnostic tests eg mass chestscreening by m iniature X-rays. This will help in detecting lesions which may or maynot be tubercular and henc e require furthe r investigation. Similarly pap smear forcancer of the cervix.The important point is that we must concentrate on the early detection of thosediseases for which early treatment is available and it is effective eg tuberculosis,diabetes, cancer of cervix and the breasts.There are three types of screening, namely:i) Mass screening i.e. screening of the whole population or the subgroupswhet]ner or not exposed to the risk of having the disease under study. It is notadvisable under the present limited resources.ji) Selective or high risk screening i.e, screening of only those who re at highrisk to have a particular problem or disease, e.g. women 35 and low er socialgroup have m ore chan ces of cancer of cervix and if they are screened for that,then there are more chances of detecting the cases. Similarly people having a

family history of d iabetes, breast cancer should be screened for such problems.iii Multiple screening n this a num ber of tests for different condition are

krouped together to screen for a number of condition at one and the sam e time egtest for lung cancer, cardiovascular diseases , diabetes, anaemia, kidney diseases,cancer of the breast and uterus, visual and audio defects are grouped together.



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rinciples nd Practice 4 6 3 Surveillanceof ommunity Healthursing The literal meaning or surveillance is supervision or close watch specially onsuspected person Epidemiologically surveillance means continuous scrutiny of thefactors that determine the occurrence,and distribution of diseases and other conditionsof ill healthIt is more than simple reporting of cases. It includes identification of missed andsuspected cases and contacts, their confirmation by laboratory investigations, finding

out source of infection, routes of transmission. This information will help in planningand implementing prevention and control of diseases in the community.The main steps involved are : collection of relevant information about the diseaseunder surveillance; analysis and interpretation of this information, dissemination of thisinformation to the concerned authority for decisions and actions leading to preventionand control of diseases, The epidemiological surveillance can be:i Individual Surveillance t includes surveillance of an infected person as longas he is the source of infection to others e.g., typhoid cases and carriers.ii Local Population Surveillance e.g., implementation of active and passivesurveillance for the prevention and control of malaria.iii National Surveillance e.g., surveillance of small pox after its eradication.iv International Surveillance surveillance of some of the important diseases likeinfluenza, polio, malaria done by W O and it provides information to the countriesin the world to take timely action.4.6.4 MonitoringandEvaluationThe literal meaning of monitoring is maintaining regular surveillance,Epidemiologically it is a specific and essentialpart of surveillance, Monitoring isongoing, day-to-day follow-up of surveillance activities which are to.be implementedas planned. This implies maintaining records of surveillance activities performed andreporting deviation to authority to take corrective measures.


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Introduction t Epidemiology

5 Defixie surveillance and mon itoring?.....................................................................................................................................

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11.1 .............................................................................................................................

6 What are the differet~t:ypes of surveilllmcel?

he science of epidemiology s basic to profession 1nursing w herever it is practiced.i A nurse working in the community deals with the people in various settings andh d p them to solve their health problems. A nurse makes use of epidemiological


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Principles and Practice process in solvingth problem i.e. she identifies and investigates the problems,of ommunity ealth formulates alternative interventions and implements the prevention and control ofNursing problem and evaluates the effectiveness of the intervention.She may deal with the problem independently especially when there are minorailments or simple health conditions and she is the only health worker in the healthagency. She may pmicipate as one of the team members especially when it is

alarge scale investigation. E.g. occurrence of any epidemic or community levelgeneral health survey or specific health survey, surveillance activities andscreening-etc. She participates in data collection data analysis, planning,iniplementing and evaluation.

ii Nurses in the community have an active role in prevention and control ofcommunicable disease which include:Participation in early diagnosis and treatment i.e. identification of all cases.Notification of certain specific diseases like measles, diphtheria, tetanus,hepatitis, rabies, STD to the health authority.Trace the contacts, keep them under surveillance.Identify the source of infection, method of spread of infection.Health education of,people in general.

iii The nurses should take notice of any uliusual occurrence of any disease in largenumbers and report the same to the authority, They also participate in itsinvestigations.iv) Nurses in the community have an important role in prevention and control ofchronic and non-infectious problems such as cardio-vascular conditions,accidents, cancer, mental health problems, etc., through health education and

helping people in their life style.Kiowledge of the basic concepts involved in the epidemiological process is essentialfor any nurse, not only thosewho are working in the community setting, Nurses playkey role in prevention and control of diseases as well as in restoring and maintainingoptimum health wherever they practice.

4 8 LET US SUM UPAfter going through this unit, you have learnt that epidemiology is the basic science ofcommunity health. Epidemiological methods such as descriptive, analytical andexperimental are useful for greater understanding of population health, communitydiagnosis, and necessary background information which helps in planning andimplementing effective health services to prevent and control various health and healthrelated problems including infectious, non infectiobs and chronic diseases.Epidemiologically there are three major categories of factors i.e. agent, host and ,environment which interact to cause various diseases. But chronic and degenerativediseases are caused due to complex interaction of multiple factors related to life style,human behavious and environmental condition known as web of causation . In theabsence of any intervention almost all diseases follow a natural cause of event whichrefers to the natural history of disease, having two phases, One phase is in theenvironment before the onset of disease and refers to 'pre pathogenesis', the secaidis in human host which start with the interaction of agent and host undqr a favorableenvironment and refers to 'pathogenesis'. h e everity of illness.#anges from mild tosevere. The sub clinical, mild undiagnosed cases remain hidden and become a sourceof infection to others,


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According to natural history of disease there are ee levels of preven tion which Introduction to Epidemiologyinclude:

Primary level prevention to prevent the occurrence of disease which includeshealth promotion and specific protection.Secondary level prevention includes measures taken during the pathogenesisphase to stop or control the spread of disease by early detection and treatment.

- Tertiary leve l prevention to limit viability and help individual to adjust thepermanent im pairment by physical, vocational and psychological rehabilitation.

The occurrence of disease mo re than no r~ n al xpectancy in a community during aspecific time is known as an epidemic which can b e du e to common source ofinfection' or du e to sp read of infection from one person to another.It is very important to do systematic investigations not only to deal with the existingproblem of the epid emic but also to deal with the problem in the future.Preventive measures w hich can be planned and implemented at the community levelto prevent and control diseases are: i conduct of health service, to determine healthneeds and problems, ii) screening for disease or detect persons with early mild andsymptomatic diseases, iii) suw eillance, monitoring and evaluation.Epidemiology is a basic requirement for preparation of comm unity health nurse and allothe'r mem bers of hea lth team to function effectiverly in the comm unity. Comm unityhealth nurses play an important role in epidemiolog ical studies of human population andtheir problem s by way of co llection of information, analysis and interpretation of theseinformation.

4 9 KEYWORDSgent

ClusteringCommunicable

: Causative factor invading a susceptible hostthrough a favorable environment to producedisease, which may be biological, chemical orphysical in nature.: Group ing offcolony oflcrowding of.: Able to be transmitted from one host to another.

Ecology : branch of biological science concerned with thestudy of inte rrelationship of organism and theirenvironment.

.Endemic : Habitual or usual presence of a disease orinfectious agent w ithin a defined geographicalarea.

Environment : The aggregated of all external conditions that mayenhance o r inhibit the interaction between host andagent; they m ay b e physical, biological, social,cultural and economical.

Epidemic : The occurrence in a comm unity or region of anillness or group of illness of similar nature clearlyin excess of normal expectation.Etiology : Cau se of a disease condition. 97


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Principlqs and Practice Hostof Community HealthNursingHypothesis

Immunity

Inc idence

A vertebrate or invertebrate species (human,animals, etc) capable of being infected or affectedby an agent.Statement showing relationship of one factor w iththe other.Insusceptibility to disease or condition,may benatural or acquired.A measurement of the number of new cases of adisease or other event occurring in. a populationduring a given period.

Infection

Morbidity

MortalityPandemic

Prevalence

ScrutinySusceptible Host

Th e entry and development or m ultiplication of aninfectiou s agents in the body of host; notsynonym ous to disease.Illness or some other conditions, no t includingdeath.Death.A n epidemic over a wide geographical area, oreven worldwide.Measuremen t of all cases (old or new) of diseaseo r other conditions present in a population at agiven time.Close or detailed exsunination, critical gaze.Sensitive host i.e., the host who does no t 'haveimm.unity.

4.10 ANSWERS TO CHECCK YOU PROGRESSCheck Your Progress 11 Epidemiology is the study of frequency, dish but ion and determinants of healthrelated states/events ai~d orbidity patterns in population and the applications ofthis study to control health problems.2) To determ ine the morbidity pattern , health related States and even ts and theirdeterminants for the.purpose of planning and implementing comprehensive healthcare services.3 Mode rn epidem iology not only deals with study of frequency, distribution ahddeterm inants, disabilities Ad mo rtality among people but also those hkalth relatedconditions and events and situation which have direct or indirect effect on-healthof the peop le. It also deals with planning,implemeriting, evalua ting andmonitoringbf health services.Check our progress 21) Germ theory : epidemiologicid dlad web of causation, determinants of health.2 Epidemiological triad theory ex plains that the disease is caused due to interactionof three categ ories of facto rs which include host, agent nd environment. Thistheory d iffered from germ theory which explains t t there is on e shingle specific

98 causative gent to every disease i.e. one cause one effect whereas according


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Principles and Practice (b) mak ing comparison of two different groups one with the problem and otherof Community Health without the problem and to find why it is so? i.e, the factor causing the problem.ursing Com parison can also be made of two groups one exposed to the risk factor andthe other not exposed to the risk factor and to observe the effect over a period oftime.

2 Desc riptive epidemiology is a method of study of occurrences and distribution ofdisease and health related events in a population by person, time and place. Thismethod helps to know he community health status and make diagnosis i.e.determine health deficits, health threats and foreseeable crisis situation andpossible associated facto rs as discussed in community identifica tion unit.

3) ~ n a l y t i c a l tudies are do ne on the basis of etiological clues obta ined bydescriptive studies i.e. the se studies go beyond descriptive studies and he lp indetermining the causative factors. Thus this method have contributed inunderstanding the causative factors and natural h s t o ~ y f the disease.4 Case con trol method is retrospective i.e. the disease have already occurred andthe investigator investigates the etiological factor i.e. the direction is from effectto cause . Whereas in case of cohart study, the disease have yet not o ccur ~ ed utpeople are exposed to the iisk factor under study. The investigator makesobse rvation over a long period of time of the expected outcomes. Cohslrt study isprospective in nature. In this, the direction is from cause to effect.5 Experimental studies are impostant because these studies help to (a) confirm thecause and effect association of the disease, and (b) evaluate or assess theefficacy of preventive or therapeutic agent or procedure. Experimental studiesare comp arative studies like analytical studies but are d ifferent from analy ticalstudies in their design . In experimental studies, the condition unde r careful controlof investigator. Th e investigator administers an interventionltreatme~lt o theexperimental group but not in the control group which is similar Lo the

experimental group in all its charac teristics.heck Your Progress

1 See th e definition given in the text.2 In common source epidemic it if is due to single exposure, there is cluste ring andsudd en explosion of the cases and rapid fall in case. If it is due to contin uuus orrepeated exposure, epidemic are not explosive, but il.regulas ~m xtended overperiod of time i.e. beyond the range of one incubation period. I n propagatedepidemics, the epidem ic is due to porlion to person contact. It flares gradually

depending upon herd immunity, opportunity for contac t. It gradually fall off.3 Inves tigation of epide c help to:confirm the existence of epidemic,know the population at risk,find out all cases,understand underlying factors causing epidemic, andfoilnulation and implementationof alternative actions that will help preventand control of the existing epidemic and epidem ic in future.

heck Your Progress1) Health Surveys are investigations to identify problem s of health and dis eas e inco mn un ity and the factors affecting them. The health surveys can be general nd

100 specific and these can be cross-~ect~iionalnd longitudinal. I


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See definition given in the text. Introduction t pidemiologyThe purpose to identify persons from normal population, who have high possibilityof having a disease under study.a Mass screening - screening of whole population.b Selective or high risk screening creening only those people who are at highrisk of problem u nder study.c Multiple screening.See the definition in the tex t.Individual surveilla~lc e,ocal population surveillance,national surveillance andinternational surveillance.

7 a Identificatibn of conlrnunity health stalus and making diagnosis i.e.,determ ination of health deficits , health threats, foreseeable crisis situation andpossible assoc iation of factors.b Planning and evaluation and monitoring of health care services.c Study of natural history of diseases.d Conform ing the cause and effect relationship.e Evaluating and assessing the efficacy of the prevention and therapeuticagents.

Identification of epidem ics, people at risk and accordingly plan and ilnpleinentservices.

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