EPIDEMIOLOGYEPIDEMIOLOGY

THE term epidemiology derived from three Greek words—1.EPI—upon

/among- 2 demos--- people 3 logos/among- 2.demos--- people.– 3.logos—science/ study.

DefinitionDefinition.

• The branch of medical science whichThe branch of medical science which treats epidemics.

• The science of infectious diseases• The science of infectious diseases.• The study of the distribution and

d t i t f h lth l t d t t ddeterminant of health related states and events in the population and the

li ti f th t d t t l h lthapplication of the study to control health problems.

AIM OF EPIDEMIOLOGYAIM OF EPIDEMIOLOGY

• 1. TO describe the distribution and size of1. TO describe the distribution and size of disease problems in human population

• 2.To identify aetiological factors in the2.To identify aetiological factors in the pathogenesis of disease.

• 3.To provide the data essential to the3.To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and ptreatment of disease and to the setting up of priorities among these services.

USES OF EPIDEMIOLOGYUSES OF EPIDEMIOLOGY

• 1. To study the effects of disease state in a1. To study the effects of disease state in a population over a time and predict future health needs.

• 2.to diagnose the health of the community.• 3.To evaluate health services.• 4.To estimate the individual risk from group

experiences.• 5.To identify the syndrome ..• 6.To search for causes of health and disease.

LEVEL OF PREVENTIONLEVEL OF PREVENTION• 1.PRIMARY PREVENTION: primary prevention p y p

is true prevention , it precedes disease or dysfunction and is applied to patients considered physically and emotionally healthy It is aimed atphysically and emotionally healthy. It is aimed at intervention before pathological changes have begun during the stage of susceptibility..g g g p y

• Health education• Good nutrition.• Attention to personality developmental.• Provision of adequate housing.

Secondary preventionSecondary prevention

• It focuses on the individuals who areIt focuses on the individuals who are experiencing health problem or illnessses.

• Its efforts seek to detect disease early and• Its efforts seek to detect disease early and treat it promptly.Th l i t di t it li t• The goal is to cure disease at its earliest stage.

Tertiary prevention

• Tertiary prevention occurs when a defect orTertiary prevention occurs when a defect or disability is permanent. it includes limitation of disability for person in the early stage of illness and rehabilitation,

• In tertiary prevention mainly the activities are directed at rehabilitation rather then diagnosis and treatment .care at this level aims to help the patient to achieve as high a level of functioningpatient to achieve as high a level of functioning as possible,deposite the limitation caused by illness or impaired functioningillness or impaired functioning.

IMPLICATION OF EPIDEIOLOGY IN C H NURSINGIN C. H.NURSING.

• Epidemiology is the basic science of communityEpidemiology is the basic science of community health. Epidemiology refers to both methods used in the study of diseases causation and the body of knowledge that arises from investigation. Epidemiology methods such as measures of h lth t l f i ithealth ,serve as tools for assessing community needs and evaluating the impact of community health programmes of disease prevention andhealth programmes of disease prevention and health promotion.

Con implication of epiCon….implication of epi.

• The knowledge derived from epidemiologyThe knowledge derived from epidemiology studies, including natural history and patterns of disease occurrence andpatterns of disease occurrence, and factors associated with high risk for developing disease serve as andeveloping disease, serve as an information base for community health nursing practice this knowledge providesnursing practice. this knowledge provides a framework for planning and evaluating community interventioncommunity intervention.

Con implication epiCon…implication..epi

• Community health nurses play anCommunity health nurses play an important role in epidemiological studies. They often may be the one to initiate aThey often may be the one to initiate a study and more frequently assist in the data collection In actual practise thedata collection . In actual practise the community health nurse is considered as the foot soldier in the army ofthe foot soldier in the army of epidemiology.

Methods and tools of id i l i l diepidemiological studies.

• Epidemiological approaches toEpidemiological approaches to relationship studies fall into two broad categories.g

• 1.observational.• 2.experimental.2.experimental.• **OBSERVATIONAL studies fall into two

main classification.main classification.• (a) Descriptive .• (b) Analytical• (b) Analytical.

CON.. OBSERVATIONAL STUDIES EPISTUDIES.EPI.

• (A). Descriptive epidemiology.:It is the study of(A). Descriptive epidemiology.:It is the study of the amount and distribution of disease or health status within a population by person, place and time .It usually involves the determination of incidence, prevalence, and mortality rates for di i l l ti Th d i tidiseases in large population. The descriptive epidemiology is the first phase of investigation in which data are obtained from such sources aswhich data are obtained from such sources as vital records and vital statistic, census information, surveys and disease report. , y p

Con Observational studies epiCon.. Observational studies epi.

• (b)Analytical epidemiology :: Analytical(b)Analytical epidemiology :: Analytical epidemiology is concerned with the searching for the underlying causes Itsearching for the underlying causes. It main purposes are to uncover the source and mode of spread of disease The clueand mode of spread of disease . The clue about the origion,nature and size of problem is discovered and the factorproblem is discovered and the factor which cause the disease are uncover.

** :Experimental epidemiology :Experimental epidemiology

• The experimental studies are undertakenThe experimental studies are undertaken to confirm an aetiogical hypothesis and evaluate or assess the effectiveness of the therapeutic or preventive measures before applying them to community. these

i t l t di b d t d iexperimental studies may be conducted in the laboratory or in the field. Pigs, mice, monkeys and other animals are frequentmonkeys and other animals are frequent used for studying the effect of drugs, vaccines and nutrientsvaccines, and nutrients.

Con.. Types of experimental distudies

• In epidemiology , there are two types of p gy , ypexperiments:

• 1.Prophylactic trials: designed to prevent di di i i hi h h ffi fdisease or condition, in which the efficacy of a prevention or therapeutic agent is tested on individual e g BCGindividual .e.g. BCG.

• 2.Therapeutic trial is to treat and established disease process, in which group people as a whole is used to determine the efficacy of a drug.e.g.the evaluation fluoride in preventing dental cariesdental caries.

MODE OF DISEASETRANSMISSIONDISEASETRANSMISSION

COMMUNICABLE DISEASES CAN BE TRANSMITEDFROM THE RESERVIOR OR SOURCE OF INFECTION

TO A SUSCETIBLE HOST IN A VARIETY OF WAYS.

(A).DIRECT TRANSMISSION.

• 1 DIRECT CONTACT (AIDS LEPROSY SKIN )• 1.DIRECT CONTACT.(AIDS,LEPROSY,SKIN )• 2.DROPLET INFECTION.(TB, COMMON COLD)• 3.CONTACT WITH SOIL.(HOOK WORM,TETANUS)

4 BITE OF ANIMAL (RABIES)• 4.BITE OF ANIMAL.(RABIES)• 5.TRANSPLACENTAL.(VIRAL INFECTION,

AIDS,RUBELLA.)

INDIRECT TRANSMISSIONINDIRECT TRANSMISSION

• 1 FOMITES:infected feeding bottles1.FOMITES:infected feeding bottles, bedpans, urinals, handkerchiefs,

• 2 VEHICLE BORNE: Through• 2.VEHICLE BORNE: Through water,food,milk,blood, tissues, and organs.3 VECTOR BORNE V t li i• 3.VECTOR BORNE: Vector are living object which may spread the infection from

h t tone host to another.(flies,mosquitoes,cockroaches)

NATURAL HISTORY OF DISEASEDISEASE

Agent, environment and host disease processhost disease process

Definition

The st d of the distrib tion &• The study of the distribution & determinants of health related states & events in specified populations &events in specified populations & application of this study to the control of health problems (Last 1988)health problems. (Last 1988)

Application of epidemiologyThe epidemiology is useful in:

Search of cause/causes of disease/diseases.

Helps to describe the health status of population or group.

Helps to discover natural history of diseases.

Helps in controlling the disease to break the weakest link in chain of transmission ofHelps in controlling the disease to break the weakest link in chain of transmission of communicable and non communicable diseases.

Helps in planning of health Programmes and setting up of health priorities.

Helps to evaluate health Programmes and interventions.

Helps to determine the chances or probability of occurrence of disease/deaths and di bilitidisabilities.

Helps in better management of health services and hospital services.

Helps to set up cut off levels between normal and abnormal population and establishes trigger levels for action or intervention.

Major emerging and re-emerging infectious didiseases

• HIV / AIDS• Hepatitis B and Hepatitis C• Hepatitis A and Hepatitis E• Tuberculosis• Tuberculosis• Dengue• Malaria• Plague• Cholera

Swine flu (H1N1 virus)• Swine flu (H1N1 virus)• Antimicrobial resistance

Emerging diseases on the globe• Swine flu• Bird flu (H5N1 virus)• Bird flu (H5N1 virus)• SARS( severe acute respiratory

d )syndrome)• Ebola hemorrhagic fever• Hanta fever• Yellow feverYellow fever

Reasons for emergence of infectious diseasesinfectious diseases

• High population growth • Uncontrolled and unplanned urbanization• Uncontrolled and unplanned urbanization• Poor environmental sanitation• Migration of population• Migration of population• Natural disasters• Growing international trade tourismGrowing international trade, tourism• Resistance to microorganisms• Insecticide resistanceInsecticide resistance• Weak public health system• Illiteracy and ignorancey g

Chain of transmission

Infectious agent Transmission hostInfectious agentprocess

host

environments

Infectious agent• Microbiological organisms like bacteria, virus, parasites, fungi

live and multiply in hosts and environment.

Properties of Infectious agent

1. Pathogenicity : it is ability to produce disease. It can be measured by

Number of persons developing diseasep p gNumber of persons exposed to infection

2 Vi l it i f it f di2. Virulence : it is measure of severity of disease

3. Infectivity :it is ability of an organism to invade and produce3. Infectivity :it is ability of an organism to invade and produce infection in the host.

Transmission process• Methods Of transmissionDirect transmission

1. Direct contact – sexual relations, kissing, touching, child birth2.Droplet infection3.Contact with soil3.Contact with soil4.Inoculation into skin or mucosa5.Transplacental

Indirect transmissionIndirect transmission1.Vehicle- borne2.Vector- borne- mechanical & biological3.Air- borne- droplet nuclei & dust4.Fomite- borne5.Unclean hands and fingers5.Unclean hands and fingers

Direct Transmission

HIV

• Over 84% transmission is through unprotected sexual intercourse. HIV positive people look p p phealthy for considerable time and can transmit the virus to others.Implications: modification of risky sexual behavior of young people.

For other STDs ,other strategies are early diagnosis and treatment.

Blood Transfusion• Unsafe blood can transmit HIV, hepatitis B and C,

hili d l isyphilis and malaria.• implication : screen all the blood collected in the blood

b k d di d th iti ith i f tibank and discard the ones positive with infection.Transplacental transmissionP t th f tPregnant mother fetus• Risk to mother to child transmission (MTCT) can be

t ll d b i l l d f N i i t thcontrolled by a single oral dose of Nevirapine to the mother at the onset of labor and single dose to the baby within 72 hrs of deliverybaby within 72 hrs of delivery.

Air Borne Transmission

coughsEx. Tuberculosis

TB bacilli can remain viable inTB bacilli can remain viable in wet sputum for months and in dried sputum for weeks.

Laughs and sings

sneezesTB patientImplications :

•Covering nose and mouth during coughingduring coughing •Safe disposal of sputum•Early diagnosis and treatment

talksEarly diagnosis and treatment

Indirect Transmission• VEHICLE BORNE TRANSMISSIONContamination through infected water and food

can cause :Diarrhea CholeraTyphoid DysenteryHepatitis A and E Polio pImplication :

Provide safe water free of germs with safeProvide safe water free of germs with safe levels of fluoride and heavy metals Construction of sanitary latrinesConstruction of sanitary latrinesHealth education

• Vector borne transmissionDiseases spread by insects .Transmission by a vector may be mechanical or biological.a. Mechanical transmission -The infectious agent is mechanically transported. Transmission of infectious agent by flies etc.

b Bi l i l t i i Th i f ti t d i li ti d l t b thb. Biological transmission- The infectious agent undergoing replication or development or both in vector & requires an incubation period before vector can transmit. It is of three types

i) Propagative- the agent multiplies in vector , no change in the form e.g. Plague bacilli in rat flea.

ii) Cyclo-propagative- Agent changes in form & no. e.g. malaria parasite in mosquito.

iii) Cyclo -developmental- agent undergoes development, no multiplication e.g. microfilaria in mosquitoq

Name of the vector Disease transmittedAnophleline mosquito MalariaAedes aegpti Denguegp gCulex Japanese encephalitis,filariaSand fly kala azarRat flee PlagueLouse Typhus feveryp

Implications :malaria and filaria are major public health problems.

National vector borne disease control programmecontrol programme

• Source reduction : controlling breeding placesSource reduction : controlling breeding places, anti larval measures, anti adult measures

• Use of insecticides by spraying and fogging• Use of insecticides by spraying and fogging , use of bed netsBi l i l f G b i fi h th t• Biological measures: use of Gambusia fish that eats mosquitoes

• Waste management

Parentral Transmission

• modes Common infections :• HIV• Hepatitis B and Cparentral

IMPLICATIONS:C

bloodControl drug menaceChange of behaviorSafe auto disabled syringesSafe auto disabled syringes and needlesScreening of blood

needlessyringes

g

Unclean hands and Fomites• Transmit feco-oral diseases like diarrhea

and worm infestation.and worm infestation.• implications:

H d hi ti h ld b• Hand washing practice should become universal habit. It reduces incidence of di h b b t thi ddiarrhea by about one third.

Host in chain of infection • Source of infection- is defined as the person, animal, object or

substance from which an infectious agent passes or is disseminated to the host.

• Reservoir- is defined as any person, arthropod, plant, soil or substance in which the infectious agent lives and multiplies, on which it depends primarily for survival and where it reproduces itswhich it depends primarily for survival and where it reproduces its self in such a manner that it can be transmitted to the susceptible host.

Di R i SDisease Reservoir SourceTuberculosis Man SputumHIV / AIDS Man Body fluidsM l i M / M it Bl dMalaria Man/ Mosquito BloodRabies Dog SalivaMeasles Man DropletCholera Man Food/ WaterCholera Man Food/ WaterTyphoid Man Food/ WaterTetanus Soil Soil

• SIGNIFICANCE: • Host factors are important i di t ib ti d• If we know the reservoir and

source of infection the chain of infection can be broken

in distribution and determinants of communicable diseasesof infection can be broken

and can be effectively controlled. Example: in TB we treat the reservoir by A d

genes

we treat the reservoir by chemotherapy or DOTS to render the reservoir noninfectious

High riskAge and sex

noninfectious.• Where source of infection is

water, we treat it by boiling or chlorination to destroy

host occupation

Nutritionalt tchlorination to destroy

disease producing animals.status

Marital

Immunizationstatus

statusliteracy

Mechanism of entry of infectious i i th h torganism in the host

Organism RouteHookworm, rabies Skin and mucous

membraneDiarrhoea,hepatitis A and C,Polio

Oral cavity and gastrointestinal tract

TB, Influenza,pnemonia,Chickenpox, measles

Respiratory tract

Malaria ,dengue ,Filaria Insect bite – blood stream

HIV,Hep B and C,syphilis

Parentral,verticle,sexual

Host reactionsInfectious organism

Enter in human host

Produces in apparent infection recovery

Mild disease host fights or treatment

Severe disease treatment

Death disability

Infection is not equivalent to disease.

TB infection:Wh b th i i t i i

TB diseaseA f i d t dWhen a person breaths in air containing

TB bacilli, most of the larger droplets settle in nose or throat where they they are unlikely to establish infection. Fine droplets containing 1-3 bacilli may

Appearance of signs and symptoms due to multiplication of bacilli cause disease. Only 10% of infected individuals develop disease. However if HIV occurs to infected individual itdroplets containing 1 3 bacilli may

reach the alveoli

Ingested by macrophages

if HIV occurs to infected individual, it enhances the risk to 60%.

In TB disease person develops pulmonary brain bone or miliary TB

Virulent bacilli multiply in the macrophages

With i 2 4 k th h t t ll

brain, bone or miliary TB.

Diagnosis of pulmonary TB by sputum smear examination.

With in 2-4 weeks the host mounts a cell mediated immunity that will arrest infection in 90% of individuals.

TB infection means TB bacilli are viable in the body but are not multiplying and

Treatment : multidrug therapy. Directly observed treatment short course. (DOTS)

the body but are not multiplying and causing disease due to body immune system.

Carrier is defined as an infected person or animal that harbors a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection for others.

• The presence of disease agent in the body• Absence of recognizable signs and symptoms• Shedding of disease agent in the discharges thus acting as a source ofShedding of disease agent in the discharges thus acting as a source of

infection for othersTYPES1 Incubatory carrier those who shed the infectious agent during the1. Incubatory carrier- those who shed the infectious agent during the

incubation period of the disease e.g. measles, mumps, polio etc.2. Convalescent carrier- they continue to shed the disease agent during the

period of convalescence Clinical recovery does not coincide withperiod of convalescence. Clinical recovery does not coincide with bacteriological recovery.

3. Healthy carrier- emerges from sub-clinical cases4 T i h d th i f ti t f h t i d f ti4. Temporary carriers- shed the infectious agent for a short period of time.5. Chronic carriers- one who sheds the infectious agent for indefinite period.

Environments in chain of Infection• It is an aggregate of all the external

conditions and factors, which affects the life and development of an organism.

• Environment is getting worse because of rapid population growth, increased pressure on natural

environment

increased pressure on natural resources .

• Resulted in water, air, soil pollutionImplicationsImplications

To provide safe drinking waterSafe disposal of human excretaControl of breeding of insects

PhysicalWater

BiologicalOrganisms

ChemicalAgricultureControl of breeding of insects

Hospital treats patients while an epidemiologist treats both patient and environment

WaterAir

Temperatureradiation

OrganismsPlants

animals

Agriculture and

industrialwaste

Occurrence of CCDE id i Th l i it i f di ifiEpidemic- The unusual occurrence in a community or region of disease, specific

health related events or behavior clearly in excess of expected

Time Distribution single exposurecommon source

multiple exposure• Short term propagated

(Epidemic)l / dslow /modern

• Periodic fluctuation Seasonal trend

Cyclic trend• Long term/ secular

Endemic- The constant presence of a disease or infectious agent within a given geographic area or population group without importation from outside. The prevalence And incidence remain at expected level.

S di tt d b t Th i l l h h dl i f tlSporadic- means scattered about. The cases occur irregularly, haphazardly or infrequently.

Pandemic- An epidemic usually affecting a large proportion of the population or occurring over a wide geographic area.

Disease prevention & control• Epidemiological knowledge

of disease i.e. frequency, di t ib ti ti f tdistribution, causative factorsetc is required to determine the weakest link in the chain

Disease prevention and

control

of disease transmission. • This chain then can be

broken to control thebroken to control the disease.

Control of Source

and Control of

transmission

Strengthenthe

susceptiblereservoir

phost

• Controlling the reservoir1 Early Diagnosis (surveillance)1.Early Diagnosis (surveillance)2.Notification3.Epidemiological Investigation 4.Isolation5.Treatment6.Quarantine

• Interruption of transmission• Interruption of transmission1.Disinfection2. Hospital waste management3.Safe water supply and safe disposal of excreta

• The susceptible host1 Active Immunization1.Active Immunization2. Passive Immunization3. Combined Active & passive Immunization4. Chemoprophylaxis5 N ifi5.Non-specific measures

Disease prevention & control Controlling the reservoirControlling the reservoir

1. Early Diagnosis (surveillance)- Prompt detection & treatment of cases is needed for treatment of diseases for epidemiological investigation to studyneeded for treatment of diseases, for epidemiological investigation, to study the time, place & person distribution & prevention & control measures

2. Notification- Notification to the local health authority is required as soon as th di i d t t d th t i di t ti b t k t t l ththe disease is detected so that immediate action can be taken to control the spread of the disease & provide medical care to patients.

• Those diseases subject to INTERNATIONAL HEALTH REGULATIONS areThose diseases subject to INTERNATIONAL HEALTH REGULATIONS are CHOLERA, PLAGUE & YELLOW FEVER

• Diseases under surveillance by WHO- Louse borne typhus, relapsing fever, l ti li l i i flparalytic polio, malaria, influenza

• Health administrators are required to notify WHO Geneva under the International Health Regulation and International surveillanceInternational Health Regulation and International surveillance

Disease prevention & controlControlling the reservoirControlling the reservoir

3. Epidemiological investigation- is required to identify the source of infection factors influencing theidentify the source of infection, factors influencing the spread of disease & to determine the preventive & control measures.

4. Isolation- is required to limit the spread of disease from the infected person to the susceptible Thefrom the infected person to the susceptible. The duration of isolation is determined by the duration of communicability of the disease and the effect of chemotherapy on infectivity The isolation can be achemotherapy on infectivity. The isolation can be a hospital isolation or a home isolation. Isolation can also be achieved in some diseases by ring immunizationimmunization.

Disease prevention & controlControlling the reservoirControlling the reservoir

5 Treatment- treatment reduces the communicability of disease5. Treatment- treatment reduces the communicability of disease, decreases the duration of disease & prevents development of secondary cases. Treatment is also extended to the carriers. Treatment can be individual or mass treatment. If treatment is inadequate or inappropriate then drug resistance can occur.

6. Quarantine- Defined as the limitation of freedom of movement6. Quarantine Defined as the limitation of freedom of movement of well persons or animals exposed to the communicable disease for a period of time not longer than the longest incubation period of the disease in a manner to prevent contact

ith th t dwith those not so exposed. It is applied by a health authority to a ship, an aircraft, a train, other means of transport or container to prevent the spread of di i f di t f di Q tidisease, reservoir of disease or vector of disease. Quarantine applies to restrictions on the healthy contacts of an infectious agent

Disease prevention & control Interruption of transmissionInterruption of transmission

1. Disinfection – the killing of infectious agents t id th b d b h i l h i loutside the body by chemical or physical

means. All soiled articles with secretion, excretion of infectious patients are treated with ex. Hypochlorite solution, bleaching powder solution, steaming, sun drying or autoclaving

2 Hospital waste is disposed in color coded bags2. Hospital waste is disposed in color coded bags3. Safe drinking water by treatment or

chlorination of water, pasteurization of milk.4. Safe disposal of human and animal excreta by

sanitary latrines, manure pits5 Rodent control measures- trapping and killing5. Rodent control measures trapping and killing6. Control of vectors by source reduction,

antilarval and anti adult measures.

Disease prevention and controlThe susceptible host

1. Active Immunization- One effective way of controlling the spread of i f i i h h h d f I i f iinfection is to strength the host defense. It is a mass means of protecting the greatest number of people. By reducing the number of susceptible in the community, it augments “herd immunity” making the infection more difficult to spread.difficult to spread.

2. Passive immunization- Three types of preparations are available for passive immunization. Normal human immunoglobulin, Specific human p g , pimmunoglobulin Antiserum or antitoxin.

• It is a short term expedient useful when exposure to infection has just occurred or is imminent within the next few days.

• The duration of immunity induced is short and variable & undesirable reactions may occur if antiserum is of non-human origin.

• It is recommended for non-immune persons under special circumstances.

Disease prevention and controlThe susceptible hostp

3. Combined Active & passive Immunization-In some diseases like Tetanus, Rabies etc passive immunization in conjunction

ith i ti t d i d t t id b th i di twith inactivated vaccine products, to provide both immediate temporary passive immunity and slowly developing passive immunity may be given. If the injections are given on separate sites the immune response to the active agent may or may notsites the immune response to the active agent may or may not be impaired by immunoglobulin

4 Chemoprophylaxis implies the protection from or prevention of4. Chemoprophylaxis- implies the protection from or prevention of disease. This may be achieved by causal prophylaxis or clinical prophylaxis.

• Causal prophylaxis implies the complete prevention of• Causal prophylaxis- implies the complete prevention of infection by early elimination of the invading or migrating causal agent.

• Clinical prophylaxis- implies the prevention of clinical• Clinical prophylaxis- implies the prevention of clinical symptoms, it does not necessarily mean elimination of infection.

Disease prevention and controlThe susceptible hostp

5. Non-specific Measures- Improvement in the5. Non specific Measures Improvement in the quality of life, better housing, safe water supply, sanitation, nutrition, education, pp ylegislative measures, community improvement in disease surveillance, disease control etc

• Primary Health Care services provided to the population.

• Changes in behavior and life styles.