Epidemiology.Epidemiology.

Doctrine about Doctrine about epidemiological process. epidemiological process.

Classification of infectious Classification of infectious diseasesdiseases

There are as many numbers of definitions as there There are as many numbers of definitions as there are books on epidemiology. are books on epidemiology.

E. is the study etiology and spreading of E. is the study etiology and spreading of infectious diseases in a human community and infectious diseases in a human community and is aimed at prevention, control, and final is aimed at prevention, control, and final eradication of these diseaseseradication of these diseases (Prague, 1960)(Prague, 1960)..

““Study of the occurrence of illness” (Gaylord Study of the occurrence of illness” (Gaylord

Anderson, 1979) .Anderson, 1979) .

Considering the wide range of areas in epidemiologic research and the major methodologies involved a comprehensive definition would be –

Epidemiology is the study of frequency, distribution and determinants of health related events.

This is a synthesis of the major ideas given by expert epidemiologists.

Frequency – implies measurements summarized information. It is essential for comparing information and different problems or magnitude of same problem among different groups. Study of frequencies makes epidemiology a quantitative science. It may be expressed as rates or proportions. They are simple arithmetic expresions.

Distribution implies the study of the patterns of the health problem in a community. For example, which age group or gender group is more affected or which geographic area is affected or spared and what is the time of the year when problems are more or less, etc.

Determinants mean causative factors.

Information on both frequency and distribution throws light on possible causative factors.

The analytical approach in epidemiology tests the hypothesis thus made, and arrives at definite conclusions on causative factors. Biostatistics is the tool for making these measurements.

E. is a very old word dating back to 3 rd century BC. It is derived from three words in Greek: Epi = Upon + Demos = People + Logos = Study of.

E. developed into a science of separate identity during 20th century. There are references about epidemiological studies conducted many years before. Many of the epidemiologists in these formative years were physicians who were challenged by the health problems.

D. SamoilovichD. Samoilovich (1724-1810)(1724-1810)

E. Jenner(1749 - 1823)

L. Pasture(1822 - 1895)

D. K. ZabolotnyD. K. Zabolotny (1866-1929)(1866-1929)

M. F. HamaliaM. F. Hamalia (1859-1949)(1859-1949)

EE.. N N. . PavlovskyPavlovsky (1884-1965)(1884-1965)

L. V. L. V. GromashevskyGromashevsky (1887-1980)(1887-1980)

AIM OF EPIDEMIOLOGYThe International Epidemiological

Association (IEA) has listed three main aims for the science of e.

1. To describe the distribution and magnitude of health and disease problem in human population.

2. To identify etiological factors (risk factors) in the pathogenesis of disease.

3. To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of disease and to setting up of prioritiesamong those services.

Microorganisms causing i.d. Microorganisms causing i.d. parasitize on host and persist due parasitize on host and persist due to continuous reproduction of new to continuous reproduction of new generations. Then the pathogenic generations. Then the pathogenic microorganism can survive by microorganism can survive by changing its residence, via a changing its residence, via a corresponding transmission corresponding transmission mechanism. This continuous chain mechanism. This continuous chain of successive transmission of of successive transmission of infection (patient-carrier), infection (patient-carrier), manifested by symptomatic or manifested by symptomatic or asymptomatic forms of disease, is asymptomatic forms of disease, is called an called an

epidemic processepidemic process

Epidemiological processEpidemiological process – – circulation of infectious diseases circulation of infectious diseases among peopleamong people

Epizootological processEpizootological process – circulation – circulation of infectious diseases among animals.of infectious diseases among animals.

SourceSource of infectious agents is an of infectious agents is an object of natural habitation and object of natural habitation and multiplication of the pathogenic multiplication of the pathogenic microorganisms and in which they microorganisms and in which they may accumulated. Since may accumulated. Since pathogenic microorganisms are pathogenic microorganisms are parasites, only living parasites, only living macroorganism can be such an macroorganism can be such an object, a human or an animalobject, a human or an animal

Source of infectious Source of infectious agentsagents HumanHuman – – patient or carrier (patient or carrier (from the from the

end of the incubation period; prodromal end of the incubation period; prodromal period; climax period; convalescence, period; climax period; convalescence, when microorganism excretion occurwhen microorganism excretion occur) - ) - antroponosisantroponosis

AnimalsAnimals (domestic, wild) – (domestic, wild) – zoonosiszoonosis Antropozoonosis Antropozoonosis (both man and animal (both man and animal

can be the source) can be the source) EnvironmentEnvironment – – sapronosis sapronosis (tetanus, (tetanus,

legionellosis)legionellosis)

Epidemic focusEpidemic focus is the is the residence of infection source residence of infection source including the surrounding including the surrounding territory within the boundaries of territory within the boundaries of which, the source can, under which, the source can, under given conditions, transmit a given given conditions, transmit a given disease through the agency of the disease through the agency of the pathogenic microorganisms.pathogenic microorganisms.

The focus of infection remains The focus of infection remains active until the pathogenic active until the pathogenic microorganisms are completely microorganisms are completely eradicated, plus the maximal eradicated, plus the maximal incubation period in persons that incubation period in persons that were in contact with the source of were in contact with the source of infection. infection.

The combination of routes by which The combination of routes by which the pathogenic microorganisms the pathogenic microorganisms are transmitted from an infected are transmitted from an infected macroorganism to a healthy one macroorganism to a healthy one

is called the is called the mechanism of mechanism of infection transmission.infection transmission.

4 mechanisms of transmission are 4 mechanisms of transmission are distinguished according to the distinguished according to the primary localization of pathogenic primary localization of pathogenic agents in macroorganisms:agents in macroorganisms:

- Fecal-oralFecal-oral (intestinal (intestinal localization);localization);

- Air-borneAir-borne (respiratory tract); (respiratory tract);- TransmissiveTransmissive (blood circulating (blood circulating

system);system);- Contact (wound)Contact (wound) (biological (biological

fluids)fluids)

3 phases are distinguished in the 3 phases are distinguished in the transmission of infection from one transmission of infection from one person to another:person to another:

- ExcretionExcretion from an infected from an infected macroorganism;macroorganism;

- Presence in the environment;Presence in the environment;- PenetrationPenetration into a healthy into a healthy

macroorganism.macroorganism.

The method by which agents are excreted The method by which agents are excreted from an infected macroorganism from an infected macroorganism depends on the localization of depends on the localization of pathological process.pathological process.

The presence of causative agents outside The presence of causative agents outside of macroorganism (2-nd phase) is of macroorganism (2-nd phase) is connected with various environmental connected with various environmental objects.objects.

The environmental objects that transmit The environmental objects that transmit the pathogenic agents from one person the pathogenic agents from one person to another are called to another are called transmission transmission factorsfactors..

Fecal-oral mechanismFecal-oral mechanism

Air-borne mechanismAir-borne mechanism

Transmissive Transmissive mechanismmechanism

Contact (wound) Contact (wound) mechanismmechanism

Susceptibility Susceptibility is a biological property is a biological property of organism, characterized by optimum of organism, characterized by optimum conditions for multiplication of conditions for multiplication of pathogenic microorganisms. S. is a pathogenic microorganisms. S. is a species property that is transmitted by species property that is transmitted by hereditary trait.hereditary trait.

Immunity Immunity Hereditary AcquiredHereditary Acquired

(species) Natural Artificial(species) Natural Artificial

(active, passive)(active, passive)

Natural active i.Natural active i. is formed as a is formed as a result of a sustained disease result of a sustained disease (postinfection or acquired).(postinfection or acquired).

Natural passiveNatural passive – from the – from the mother to child (intrauterine). mother to child (intrauterine). Newborn acquires it with mothers Newborn acquires it with mothers milk.milk.

Artificial active immunity Artificial active immunity (postvaccinal) (postvaccinal)

develops during 3-4 weeks and persists develops during 3-4 weeks and persists from 6 months to 5 years.from 6 months to 5 years.

Artificial passive immunity Artificial passive immunity is created is created by administration of antibodies (serum, by administration of antibodies (serum, immune globulin). It persists for 3-4 immune globulin). It persists for 3-4 weeks. weeks.

Sterile immunitySterile immunity microorganism microorganism is disappear from the is disappear from the macroorganism after the macroorganism after the treatment. treatment.

Non-sterile immunity Non-sterile immunity immunity immunity persists until the pathogenic persists until the pathogenic agent remains in the agent remains in the macroorganism globulin).macroorganism globulin).

Community immunityCommunity immunity is non- is non-susceptibility of a community to a susceptibility of a community to a given infection. Created by given infection. Created by specific prophylactic and other specific prophylactic and other measures that are taken by measures that are taken by health-care services, and also by health-care services, and also by improvement of well-being of improvement of well-being of population.population.

Main motive forces Main motive forces of epidemiological processof epidemiological process::

Source of infectious agentSource of infectious agent Mechanisms of infectious agent transferMechanisms of infectious agent transfer Receptive organismReceptive organism

Secondary motive forces Secondary motive forces

of epidemiological processof epidemiological process::

Social factorsSocial factors Environmental factorsEnvironmental factors

PRINCIPLES OF EPIDEMIOLOGYPRINCIPLES OF EPIDEMIOLOGY

I principleI principle

Source of infectious agent is Source of infectious agent is infected (sick or carrier) infected (sick or carrier) organism - human or animalorganism - human or animal

(object which is the site of natural (object which is the site of natural habitation and multiplication of habitation and multiplication of pathogenic organisms, from where pathogenic organisms, from where they can infectthey can infect healthy people)healthy people)

PRINCIPLES OF EPIDEMIOLOGYPRINCIPLES OF EPIDEMIOLOGY

II principleII principle

Infectious agent’s localization in the Infectious agent’s localization in the organism and mechanism of it’s organism and mechanism of it’s transmission from one individual to transmission from one individual to another form persistent connection, another form persistent connection, which provide pathogenic species which provide pathogenic species preservation in the environment and preservation in the environment and continuitycontinuity of epidemic process of of epidemic process of infectious disease.infectious disease.

Mechanism of infectious Mechanism of infectious agent’s transmissionagent’s transmission

1st phase:1st phase: e excretion of the causative agent xcretion of the causative agent from the infected macroorganismfrom the infected macroorganism

2nd phase:2nd phase: staining of the causative agent staining of the causative agent in environmentin environment

3rd phase:3rd phase: infectious agent’s penetration infectious agent’s penetration into healthy (susceptible) organisminto healthy (susceptible) organism

PRINCIPLES OF EPIDEMIOLOGYPRINCIPLES OF EPIDEMIOLOGY

III principleIII principle

Infectious diseases can be rationally Infectious diseases can be rationally classified according to specific classified according to specific localization of infectious agent in localization of infectious agent in the organism, corresponding the organism, corresponding mechanism of transmission and mechanism of transmission and main biological properties of main biological properties of causative agent:causative agent:

intestinal infectionsintestinal infections respiratory infections respiratory infections blood infectionsblood infections infections of infections of external covers external covers

PRINCIPLES OF EPIDEMIOLOGYPRINCIPLES OF EPIDEMIOLOGY

IVIV principleprinciple

Epidemic process originates and Epidemic process originates and maintained only due to combined maintained only due to combined action of three main motive forcesaction of three main motive forces::

Presence of infectious agent’s sourcePresence of infectious agent’s source;; Realization of transmission mechanismRealization of transmission mechanism;; Population susceptibility to the infection.Population susceptibility to the infection.

If any of these factors is excluded, If any of these factors is excluded, epidemic process stop epidemic process stop

PRINCIPLES OF EPIDEMIOLOGYPRINCIPLES OF EPIDEMIOLOGY

VV principleprinciple

Natural and social factorsNatural and social factors stipulate stipulate quantitativequantitative and qualitative changes in and qualitative changes in the epidemic process (the epidemic process (increase or increase or decreasedecrease), thus they are), thus they are

secondary motive forces secondary motive forces of epidemic processof epidemic process

EPIDEMICAL FOCUSEPIDEMICAL FOCUS- site of infectious agent site of infectious agent

habituation, including habituation, including surrounding territorysurrounding territory with the with the limitslimits where it can be where it can be contagious for otherscontagious for others..

Epidemical focus exist in time Epidemical focus exist in time (maximal incubation period of (maximal incubation period of the disease) and in area the disease) and in area (determined by transmission (determined by transmission mechanism) mechanism)

ANTIEPIDEMIC MEASURES INANTIEPIDEMIC MEASURES IN THE FOCUS OF INFECTION THE FOCUS OF INFECTION

Measures concerning infectious agent’s Measures concerning infectious agent’s sourcesource

Disease diagnosisDisease diagnosis RegistrationRegistration Isolation of the patient (carrier)Isolation of the patient (carrier) Etiological treatmentEtiological treatment

Measures concerning transmission Measures concerning transmission mechanisms mechanisms

disinfectiondisinfection ( (disinsectiondisinsection, , deratizationderatization) – ) – currentcurrent, , finalfinal

Measures concerning contact persons:Measures concerning contact persons: Sanitary processingSanitary processing Medical observationMedical observation Laboratory examinationLaboratory examination Specific prophylaxis Specific prophylaxis

DEGREES OF INFECTION’S DEGREES OF INFECTION’S SPREADINGSPREADING::

1.1. Sporadic Sporadic – – normal level of morbidity normal level of morbidity for the given territory in a given for the given territory in a given period of timeperiod of time

2.2. EpidemicEpidemic – – morbidity in a few times morbidity in a few times more higher than sporadicmore higher than sporadic

3.3. Pandemic Pandemic – – extraordinary intensive extraordinary intensive epidemic process and considerably epidemic process and considerably greater than epidemic.greater than epidemic.

Endemic infections Endemic infections – – connected to connected to certain territory.certain territory.

Exotic infectionsExotic infections – – diseases, which are diseases, which are not characteristic for the local not characteristic for the local territory, but can be transferred from territory, but can be transferred from other countriesother countries..

PRINCIPLES OF INFECTIOUS DISEASESPRINCIPLES OF INFECTIOUS DISEASES CLASSIFICATIONCLASSIFICATION

((ACCORDING TO L. GROMASHEVSKYACCORDING TO L. GROMASHEVSKY))

1.1. Localization of infectious Localization of infectious agent in organismagent in organism

2.2. Mechanisms responsive for Mechanisms responsive for transmission of infectious transmission of infectious agentagent

GROUPS OF INFECTIOUS GROUPS OF INFECTIOUS

DISEASESDISEASES (according (according to to Gromashevsky)Gromashevsky)

1.1. Intestinal infectionsIntestinal infections – – are transferred by fecal-are transferred by fecal-oral mechanismoral mechanism

2.2. Respiratory infectionsRespiratory infections – – are transferred by the are transferred by the droplet mechanismdroplet mechanism

3.3. Blood infectionsBlood infections – – by means of transmissive by means of transmissive mechanism of transfermechanism of transfer

4.4. Infections of external coversInfections of external covers – – by means of by means of contact or contact-wound mechanismcontact or contact-wound mechanism

Distinguished Distinguished trans-placental trans-placental ((verticalvertical)) mechanism of mechanism of transfertransfer, , and accordingly, infections which are and accordingly, infections which are transferred by trans-placental waytransferred by trans-placental way

THE TOOLS OF EPIDEMIOLOGY

Clinical medicine, immunology, microbiology, pathology, demography, and statistics. The use of each of these tools for achieving a specific objective forms for tpidemiologic method.

Epidemiological Epidemiological methodsmethodsFor achieving the above objectives various For achieving the above objectives various

methods are used by epidemiologists. They have methods are used by epidemiologists. They have evolved from 19evolved from 19thth century: century:

1. Observational1. Observational

2. Experimental2. Experimental ObservationalObservational – as the name implies – as the name implies

involves only making observations on what involves only making observations on what has happened to persons and communities has happened to persons and communities and make inferences from these and make inferences from these observations.observations.

It may be further classified into It may be further classified into descriptivedescriptive andand analyticalanalytical..

Descriptive studiesobserve health phenomena in terms of time /

place / person.- Cross-sectional made on populations or

communities at one point of time. They give information on the community just as a cross section of a specimen gives informationat that particular level of sectioning.

- Longitudinal surveys conducted over long periods in the same population. They give information over different time points. Useful in calculating incidence rates and drawing time trends in health and disease.

Analytical designsBased on specific hypothesis

generated from cross sectional or longitudinal studies. Used to gather data and the data is analysed to test the specific hypotesis. May be called retrospective studies when both the exposure and outcome has occurred before the study commences. They are prospective when both exposure and outcomes are yet to occur.

Experimental designAre methods where suspected causal

situation is induced in selected and control populations and their effects are observed to prove or disprove a hypothesis. The major modalities of experimental designs in vogue currently may be classified as follows:

- Randomised controlled clinical trial;- Field trials;- Community trials.

Inspection – Inspection – revealing of the revealing of the sourcesource

Examination – Examination – studying of studying of morbiditymorbidity

Analysis of morbidityAnalysis of morbidity Experiment – Experiment – microbiological microbiological

and serological examination, and serological examination, physical and chemical studies, physical and chemical studies, experiment on humans and experiment on humans and animalsanimals

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