UNIT-5 PRINCIPLES OF EPIDEMIOLOGY AND METHODS

By-Mandeep kaur

BASIC TOOLS OF MEASUREMENT IN EPIDEMIOLOGY

• MORTALITY

• MORBIDITY

• DISABILITY

• NATALITY

• ATTRIBUTES OF DISEASES- PRESENT OR ABSENT

• MEDICAL NEEDS

• HEALTH CARE FACILITIES

• UTILISATION OF HEALTH SERVICES

• ENVIRONMENTAL FACTORS SUSPECTED OF CAUSING DISEASE

• PSYCHOSOCIAL ASPECT OF HEALTH

RATE• A rate measures the occurence of some particular event in a population during

a given time period.

• For example-Death rate, Birth rate, Specific rate.

• ELEMENTS OF RATE-

• Numerator

• Denominator

• Time specification

• Multiplier

EXAMPLE-Mortality

rate, Morbidity rate.

Crude Death Rate=No. of deaths in one yearx1000Mid year Population

RATIO• Ratio express a relation in size between two random quantities.

• Ratio is the result of dividing one quantity by another.

A:B OR A/B

ELEMENTS-Numerator, Denominator

For example- Ratio of available health services to utilization of health services

• Ratio of W.B.C to R.B.C

• Sex ratio

• Child women ratio

PROPORTION• It is also a ratio indicates the relation in magnitude of a part of the whole. It is

expressed as a percentage.

• ELEMENTS-Numerator, Denominator and Percentage as multiplier.

• For example-Proportion of scabies among children in a given / certain time is expressed as--

The number of children with scabies at a certain time

x 100

The total number of children in village at the same time

USES OF EPIDEMIOLOGY• Epidemiology has wider application covering the areas such as disease, health and health

services. According to Thrushfield, there are 5 use of epidemiology. He is identifying the6th use of epidemiology which is- To provide information to improve clinical decisions onindividual patient case management.

These 5 uses are as-

1. D etermination of the origin of a disease whose cause is known

2. Investigation and control of a disease whose cause is either unknown or poorlyunderstood.

3. Acquisition of information on the ecology and natural history of a disease.

4.Planning and monitoring of disease control programmes.

5. Assessment of the economic effects of a disease and analysis of the costs and economicsbenefits of alternative control programmes.

• Morris has identified 7 uses of epidemiology are as follows-

1. To study the rise and fall of disease in the population

2. community diagnosis

3. Planning and evaluation

4. Evaluation of Individual's risk and chances

5. Syndrome indentification

6. Completing the natural history of disease

7. Searching for cause and risk factors.

DISEASE CYCLE

• The infectious agents enter the susceptible host after finding aportal of entry such as respiratory tract, alimentary tract, skinetc.

• Inside the human host on getting appropriate environment, itmultiply and distrub the health equilibrium and the diseasebecome overt.

• The host defense against the infection. If the host defense issufficient to suppress the disease , then recovery starts and ifinsufficient then the patient develop the signs / symptoms ofdisease and require treatment.

There are 6 stages of disease cycle which occur in human host as described as below-

1. Incubation period2. Prodromal period3. Fastigium4.Defervescence5. Convalescence6.Defection

INCUBATION PERIOD

It is defined as the time interval between the entryby an infectiousagent and appearance of the first sign and symptom of the disease.

PRODROMAL PERIOD

This period is of short duration, which ranges from one to fourdays.The pathogenic agent multiply in human host and the vaguesystem appear .

FASTIGIUM

The symptoms are clear cut and are related to particular disease.Disease can be identified by clinical diagnosis.

DEFERVESCENCE

The body's defence begin to respond and there is decline ofinfection. The clients condition starts improving and feels better.

CONVALESCENCE

The improvement in the condition of patient occurs fast and therecovery is established.

DEFECTION

The patient's condition is improved and comes to his pre illnessstage i.e is free from illness as the recovery has occured.

LEVELS OF PREVENTION

The goals of medicine are to promote health, to preserve health, to

restore health when it is impaired and to minimize suffering and

distress. The natural history of disease provides the basis for

community health intervention.A four level model for prevention or

intervention, based on the stages of disease which includes-

1.Primordial Prevention

2.Primary Prevention

3.Secondary Prevention

4.Tertiary Prevention

PRIMORDIAL PREVENTION

It is concerned with prevention of development of risk

factors in population groups in which they have not yet

appeared.

For Example-helping children to develop healthy lifestyle so

they do not develop adult health problems like obesity and

hypertension.

PRIMARY PREVENTION

It is true prevention.Primary prevention can be defined as

action taken prior to the onset of disease, which removes the

possibility that a disease will ever occur.

It includes-Health Promotion

Specific Promotion

HEALTH PROMOTION

By merely promoting the health of the

individual and community we can

prevent a number of diseases such as

typhoid fever, TB, cholera and

nutritional diseases.Health education is

the process of enabling people to

increase control over and to improve

health.

SPECIFIC PROMOTION

It comprises those measures which are

directed to intercept causative agents of a

particular disease or group of diseases

before these agents affect people.

EXAMPLE- Immunization against

poliomyelitis.

Vitamin A supplements to prevent

nightblindness.

SECONDARY PREVENTION

Secondary prevention means the action taken to halt the

progress of a disease at its incipient stage and also prevention

of complications.Secondary prevention focuses on the

individuals who are experiencing health problems and illness

and who are at risk for developing complications or

worsening conditions.

The goal is to cure disease at its earlier stage.The specific

interventions used are-

1.Early diagnosis and treatment

2.Referral

EARLY DIAGNOSIS AND TREATMENT

The disease complications can beprevented and health can be restored bydiagnosing the disease at its early stagesand by providing the adequate treatmentaccording to the health problem.

Tertiary Prevention

According to human development report , tertiary

prevention is defined as all the measures available to reduce

or limit impairments and disabilities , minimise suffering

caused by exsiting departures from good health and to

promote the patient's adjustment to irremedial conditions.

Tertiary prevention includes-

1.Disability limitation

2.Rehabilitation

DISABILITY LIMITATION

The sequences of events in disabilityare-Disease----Impairment----Diability----Handicap.Disability interventions are aplied inthe late pathogenesis phase tomnimize suffering and to promotethe patient's adjustment tountreatable conditions.The objectiveof it is to prevent the transition ofthe disease process .

REHABILITATION

Acc to WHO rehabilitation is" Thecombined and coordinated use ofmedical, social, educational andvocational measures for training andretraining the individual to the highestpossible level of functional ability"OBJECTIVES-To adopt all measures toreduce the impact of disability andhandicapped.

• Rehabilitation can be achieved by physiotherapy, occupational therapy , speech therapy, educational and vocational guidance etc.

• The various aspects of it are-

1. MEDICAL REHABILITATION-restoring and retraining the functional ability of anindividual. For eg-Teaching various exercises in physiotherapy department as in case ofpolio.

2.VOCATIONAL REHABILITATION-means makina an individual capable to earn hislivelihood .For eg- training the blind and mentally retarded individuals to make candles orweave the chair.

3.SOCIAL REHABILITATION-means restoring family and social relationship.this is achievedwhen an individual starts participating actively in community life.

4.PSYCHOLOGICAL REHABILITATION-means restoring the dignity and confidence ofdisabled and cripped individual.Guidance and counselling techniques can be used torehabilitate.

DYNAMICS OF DISEASE TRANSMISSION

It involves the chain of infection.1.SOURCE OF RESERVOIR-Any person, animal, plant, soil orsubstance in which an infectious agent normally lives and multiplies.The reservoir typically harbors the infectious agent without injury toitself and serves as a source from which other individuals can beinfected. The infectious agent primarily depends on the reservoir forits survival. It is from the reservoir that the infectious substance istransmitted to a human or another susceptible host.

DISEASE TRANSMISSION DIRECT AND INDIRECT

The disease is transmitted from the reservoir to susceptible hosteither directly and indirectly by a single or several routes.The modeof transmission of infectious agent is classified as-1. Direct Transmission-When the disease is transmitted directly fromthe source of infection to susceptible host.2. Indirect Transmission -When the disease agent is transmittedindirectly to susceptible host.

MODE OF TRANSMISSION

DIRECT TRANSMISSION

1.Direct contact

2.Droplet Infection

3.Contact with soil

4.Inoculation into skin

or mucosa

5.Transplacental(vertic

al)

INDIRECT TRANSMISSION1.Vehicle borne-Water, food,

milk.

2.Vector borne-mechanical,

biological

3.Air borne-Dust,Droplet

nuclei

4.Fomite borne-soild linen

5.Unclean hands and fingers

DIRECT TRANSMISSION

1. DIRECT CONTACT-Infection may be transmitted by direct contactfrom skin to skin, mucosa to mucosa, mucosa to skin of the same oranother person.e.g- skin to skin contact or by touching, kissing orsexual intercourse. STD, AIDS, leprosy etc are transmitted by directcontact.

2.DROPLET INFECTION-This is direct projection of a spray of dropletsof saliva during coughing, sneezing, speaking and talking intosurrounding atmosphere.eg-common cold, whoophing cough, TB,many infection of nervous system.

3. CONTACT WITH SOIL-This refers to accquiring a disease agent by directexposure of susceptible tissue to disease agent in soil, compost ordecaying vegetable matter .e,g hookworm larvae, tetanus etc.

4.INOCULATION INTO SKIN-The disease agent may be inoculated directlyinto the skin or mucosa e.g- hepatitis B VIRUS through contaminatedneedles and syringes and rabies virus through dog bite.

5.TRANSPLACENTAL TRANSMISSION-Disease agents can be transmittedtransplacentally.TORCH AGENT come in this category. T-Toxoplasma gondii,R-Rubella virus, C-Cytomegalovirus, H-herpes virus.

INDIRECT TRANSMISSION

1.VEHICLE BORNE-Transmission of the infectious agents through theagency of water, food(raw vegetables, food, milk),ice, blood, serumplasma or biological products such as tissues and organs.Diseasetransmitted through water and food include-diarrhoea, typhoid ,cholera, food poisoning. Contaminated blood can cause hepatitis B,malaria, syphilis.

2. VECTOR BORNE-Vectors are intermediate living objects which mayspread the infection from one host to another.Acc to involvement of vector and propagation of parasites, is of two typesas discussed below-1.Mechanical transmission2.Biological transmission

3.AIR BORNE-The airborne infections occur by droplet nuclei and by dust.1. Droplet nuclei-They are tiny particles and remain in air for long periodof time. These are easily drown from air into the lungs and retain therecausing a disease. Example- TB, Influenza, chicken pox.

.(b)DUST-is the larger droplet particles which is released into airduring talking, coughing or sneezing etc. and settle down by theirsheer weight on floor, carpets, clothes, bedding, linen and becomepart of the dust.Disease carried by infected dust includestreptococcal infection, pneumonia, TB, Q- fever.This is commontype of transmission in hospitals.

4. FOMITE BORNE-Fomites are inanimate particles or substanceother than water or food contaminated by the infectiousdischarges from a patient and capavble of transferring theinfectious agent to a healthy person.Disease transmitted byfomities include diptheria, typhoid fever, eye and skin infections.

5. UNCLEAN HANDS AND FINGERS-Hands are the most commonmedium by which pathogenic agents are transferred to food fromthe skin, nose etc.as well as from other foods.Examples includediptheria, typhoid fever, eye and skin infections.

SUSCEPTIBLE HOST

A susceptible host is a member of a species population who is at riskof becoming infected with a certain disease due to a variety ofreasons. Susceptible hosts differ from the general populationbecause they are far more likely to get infectious diseases than thegeneral population.Examples of risk factors include poor personalhygiene, poor control of infection throughout the environment andthe age of the host. These factors all contribute to the host's abilityto become easily infected with a disease when exposed.

CONTROL OF INFECTIOUS DISEASE

Each disease has certain weak points susceptible to attack.The basicapproach in controlling disease is to identify these weak points andbreak the weakest links in the chain of transmission.This requireknowledge of disease that is its magnitude, distribution in time,place and person,source of infection and dynamics of transmission.The control of disease implies mainly the prevention ofdisease.Disease control is a continuous process, it involves followingmeasures-

1. CONTROLLING THE RESERVOIR

(a)EARLY DIAGNOSIS-It is needed to treat patients, trace the sourceof infection, to study distribution of disease and apply controlmeasure.(b)NOTIFICATIONS-Local health authority should be notified, so thatit can implement control measures.(c)EPIDEMIOLOGICAL INVESTIGATIONS-It is done to identify sourceof infection such as climate socio-cultural and behavioural related tospread of infection.

(d) ISOLATION-It is defined as -Separation for the period ofcommunicability of infected person or animals from others in suchplaces under such conditions , as to prevent or limit the direct or indirect transmission of the infectious agent from those infected tothose who are susceptible or who may spread the agent to others.(e)TREATMENT-using effective drugs cuts short duration of diseaseand interrupts its transmission.(f)QUARANTINE-means freedom of movement of such well personsor domestic animals as exposed to communicable disease for aperiod of time not longer than the longest incubation period ofdisease.

2.INTERRUPTION OF DISEASE

It consists of preventing infective agent from entering the body of asusceptible host by purifying water, many water borne disease canbe prevented e.g like typhoid, cholera can be prevented.If transmission is through vectors, vector control measure will helpto prevent transmission of disease such as by destroying mosquitobreeding places , malaria, filaria and dengue can be prevented.

3. IMMUNIZATION OF THE SUSCEPTIBLE HOST

Immunization strengthens the susceptible host , thereby, chain oftransmission of communicable disease is broken.Immunizationproduces immunity by which body develops or receives antibodiesto fight against specific disease.The government of India has recommended National Immunizationschedule to protect infants, children and pregnant women fromvarious communicable disease.

4.CHEMOPROPHYLAXIS

It means protection from or prevention of disease usingchemotherapeutics.EXAMPLE-Prevention of clinical symptoms of cholera by tetracyclineor furazolidine for household contacts.

5.NON SPECIFIC MEASURES

Such measures as im provement of general sanitation, nutritionalstatus and education have an important role in controlling andpreventing disease.The objectives of disease control are-a)Reducing the incidence of diseaseb)Decreasing the duration of illnessc)Decreasing the possible complications.d)Decreasing the mortality and morbidity.

DISINFECTION

1.DISINFECTANT-is an agent which kilss infectious agents outside the bodyby direct exposures to the chemicals.

2.DISINFECTION-Killing of infectious disease out of the human bodyby useof chemicals

3.ANTISEPTIC-An antiseptic is an agent which destroys the growth ofinfectious agents, which can be applied on living body e.g-dettol or alcohol.4.Deodorant-is an agent which suppresses bad odour.e.g-lime or bleachingpowder.

DISINFECTION

5.DISINFECTATIONS-ANy physical or chemical process which destroysbacteria, disease spreading germs or vector and vehicles of disease such asinsects, parasites, rodents and animals.

6.STERILIZATION-Destruction of microrganism and their spores.

7.Detergent-Asurface cleansing agent which act by lowering surface tensione.g-soap, which removes bacteria with dirt.

TYPES OF DISINFECTION

1.CONCURRENT DISINFECTION-Infectious

organism is destroyed

as soon as discharged

from infectious person.3.PROPHYLACTIC

DISINFECTION-Use of

disinfective measures to

prevent spread of infection

such as boiling of water ,

hand washing etc

2.TERMINAL INFECTION-Use of disinfective

measures after removal

of body of diseased

person

TYPES OF DISINFECTION

NATURAL DISINFECTANTS-1.Sunlight

2.Air

PHYSICAL DISINFECTANTS-1.By heat

2.Moist Heat 3. Radiation

CHEMICAL DISINFECTANTS-1.Liquids

2.Solids 3.Gases

TYPES OF DISINFECTION

1.NATURAL AGENTS-(a)SUNLIGHT-Direct exposure to sunlight is an effective measure for killinginfective organisms.Therefore bedding furniture etc are exposed to strongsunlight for longer period for disinfection.(b) AIR- act by drying or evaporating the moisture which helps to breed thebacteria causing infection.

2.PHYSICAL AGENTS-(a)BURNING-Inexpensive articles, useless articles such as rags, useddressings material can be disposed of by burning.Needles too can besterlized by burning for 3 seconds.

DISINFECTION

2.BOILING-in

water for at least

20 mts. helps to

disinfect the

articles like

needles, rubber

gloves etc.

4.STEAM UNDER

PRESSURE-attains

deep penetration hence

disinfection destroys

bacteria and their

spores.It is used in

hospitals and laboratory

practices.

3.PASTEURIZATION

-It is used for

sterlization of

endoscorphic

instruments, which are

heated upto 80dg.C

for 20 mts.

STREAM UNDER PRESSURE

(a)AUTOCLAVE-(b)PRESSURE COOKER3.CHEMICAL AGENTS-The articlesw which cannot be sterlized by autoclavingcan be sterlized by chemicals.Classified as follows-

1.

•PHENOL AND RELATED COMPOUNDS

•Phenol, Cresol, Cresol emulsions,Dettol

2.

•DETERGENTS

• Soap, Cetrimide,Savlon

3.

•HALOGENS

•Chlorines.Iodine,Iodopers

4. Oxidising agents

5.Miscellaneous-Alcohol,Methylted

spirit,Formalin.

CHEMICAL DISINFECTION AGENT

pp

1.PHENOL AND RELATEDCOMPOUNDS

1.PHENOL-is a cheap and

effective disinfectant.It is used in hospitals or for domestic purposes is a

crude phenol(phenol+cresol).It is effective against vegetative

gram+ and -bacteria.

2.CRESOL-It is an

excellent coal tar disinfectant. 5to10% cresol is used to disinfect faces, urinals, spectrum etc.It is

also used with other compoundswhich are

known as lysol, izal and cyllin called cresol

emulsions.

3.DETTOL-It is used for

sterilizing instruments and plastic tins.It is a highly

effective antiseptic against gram + bacteria.

CHEMICAL DISINFECTION AGENT

OTHER LIQUID CHEMICAL AGENTS-1.DETERGENTS-Soap, Savlon-Clinical thermometer can be disinfected in 1.6savlon solution,Cetrimide-can be used in cleaning wounds2.HALOGENS-Chlorines,Iodine,Iodopers3.OXIDISING AGENTS4.MISCELLANEOUS-Alcohol, Methylated Spirit,Formalin

CHEMICAL DISINFECTION AGENTS(SOLID)

1

1.LIME-This is sprinkled in public places

where open area filled with urine or faeces.

2.BLEACHING POWDER-Used as

purification agents of water, deodorant for

removing foul smell and odour.

3.POTASSIUM PERMAGANATE-It

is used for mouth wash and as disinfectant in

cleaning of fruits and vegetables.

CHEMICAL DISINFECTION AGENTS(GASES)

1

1.FORMALDEHYDE-Gas is used for

disinfecting the room. when the room is

filled with gas it is closed for 12 hours for

full disinfection.Disinfection of books, bed,

blankets can be done this way.

2.ETHYLENE OXIDE-has been used

in sterilizing plastic eqipments, cardiac

catheters etc.