General epidemiology.

DR.P.P.SINGH

ALL INDIA INSTITUTE OF LOCAL SELF GOVERNMENT

DELHI

“GENERAL EPIDEMIOLOGY OF COMMUNICABLE DISEASES”

For Para medicalsBy

Dr. P.P.SINGHFaculty AIILSGD

Ex Medical Superintendent Cum Consultant pathologist HRH Delhi

Ex. Director India Population Project 8 Delhi..

GENERAL EPIDEMIOLOGY OF COMMUNICABLE DISEASES

1. Any deviation from Normal.

2. Health is a dynamic concept.

3. to measure the extent of mortality & morbidity.

4. How disease occurs , spreads ?.

5. How to controlled , prevented and eradicated?

DEFINATION The study of distribution and

determinants (causes) of disease or health related events is called Epidemiology.

Epidemiological studies helps to seek answer to;

WHY. Where ,How When & Who. With reference to the disease.

Causation of Disease

1. Demons or Evil sprit theory( pre scientific era).

2. Germ Theory of disease

Disease agent-------------- man -------------- Disease ( Microbes)- bacteria, virus protozoa etc.`

Epidemiological TriadAgents

HOST Environment

MULTI-FACTORIAL CAUSATION OF DISEASE

Petten Koefer of Munich proposed this theory.

It has been Now realised that both communicable or non communicable diseases are of multiple factors ( RISK FACTORS)

Thus populations can be grouped in 3 groups.

1. Diseased group.

2. Population group at risk of developing disease.

3. Normal healthy group.

Natural History of Disease 1. Pre Pathogenesis Phase ; the

process in Environment.

2. pathogenesis Phase : the process in man .

Pre Pathogenesis phase ;- This is the period before the onset of disease in man . The agent has not entered but factors favoring entry are existing in the environment. ( Man exposed to high risk factors).

Pathogenesis Phase ;- This begin with entry of agent in susceptible host -- incubation period - sub clinical stage – Clinical stage – recovery stage/ mortality or carrier or normal stage.

ICE BERG PHENOMENA of Disease.

Clinical Case

Pre symptomatic cases

What the Doctor see

Floating Tip. Clinical case.

Submerged portion are hidden case.. 1 Sub Clinical case.2. Latent.3.undignosed.4. Un noticed .5.incubatory.6 healthy carriers ( Reservoir ) ( Source)

CONTROL of DISEASE

SOURCE

Channel of Transmission

Susceptible Host

Cases/ Carriers Air, water, Food MalnourishedEnvironment Fomite, Vector High risk Behaviors

Immune suppression

Prevention of Disease 1, Primordial prevention --- By Human cloning.

2. Primary prevention –a) Health Promotion – Health life style ,

Balanced diet , family planning.b) Specific protection – Vaccination , wearing

gloves , protective masks.

3. Secondary prevention –a) Screening for disease ( Clinical or Lab

investigations )b) Early diagnosis and Treatment .

4. Tertiary Prevention—a) Disability Limitation – spectacles / ear

protection b) Rehabilitation – Prosthesis etc

SANITATION BERRIER.

FOODFLUIDFAECES Disease FOMITESFLIES

DYNAMICS of DISEASE TRANSMISSION.1. SOURCE of INFECTION

1. Man himself, (Case or Carrier )2. Infected animals - Disease due to animal is called

ZOONOSES .

2. MODE of TransmissionA. Direct Transmission

I, Direct contact.ii, Droplet infection.iii, Contact with infected Soil.iv, Inoculation in to Skin or Mucosa.v, Trans placental or Vertical

transmission.B. Indirect Transmission.

I, Vehicle – borne transmission.ii, Vector – borne transmission.iii, Air borne transmission.iv, Fomite – borne transmission.

Direct contact --- Kissing , Sexual eg. Syphilis, HIV/AIDS , scabies Skin Sepsis.

Droplet infection – Small fine saliva particles containing micro organism while coughing, sneezing, talking laughing etc eg, Diphtheria, whooping cough tuberculosis etc.

Contact of soil. Eg Tetanus , hook worm , strongyloides .Inoculation into Skin – through Bite , Injection eg Hepatitis B. Rabies

Trans placental - from mother to chiled . Also known as vertical eg Toxoplasma ,rubella, hepatitis AIDS,

1.Vehicle borne Transmission - water , milk food , blood serum plasma & other biological products. Eg . Cholera, typhoid, GE, Hepatitis etc.

2.Vector borne transmission – Mosquitoes, Flea, bugs sand flies etc eg Malaria, kala azar , Plague

3.Air borne transmission –I, Droplet ii, Infected dust eg pneumonia, tuberculosis strepto- staphylococcal infections .

4.Fomite borne transmission - handkerchief , glasses door handles towels clothing , toys etc.

IMMUNITYDefinition

Ability of Body to recognise , destroy and eliminate antigenic (Foreign ) material is called Immunity.

ANTIGEN – is the substance that stimulate the formation of antibodies.

ANTIBODIES – are immunoglobulin (Proteins) formed in response to the antigens.

Types Of Immunity. A. Humeral. –

I, - are based on the production of antibodies.

ii, - These react with same antigen .

iii,-These recognise and stick to specific antigen.

iv, - The combined antigen & antibodies are engulfed by Macrophages destroyed and eliminated from the body.

v, - The antibodies circulate in blood & body fluid keeping vigil for same antigen

B. Cellular.

CELLILAR IMMUNITY .It is more complex . It is based on a type of White cell( W B C ), known as T cell Lymphocyte.

. The T cells are activated against the pathogenic agent which are intracellular .

The Humoral and Cellular components both cooperate each other and help to resist many infections.

Classification of Immunity.A.Natural Immunity. – Inherited

Immunity comes by virtue of genetic make up. This is the reason some diseases which occur in animal do not occur in Man (eg Rinderpest) similarly some man’s disease do not effect the animal eg Typhoid.

B.Acquired immunity

Acquired immunity(a) Active immunity ;-

It is the immunity develops as a result of infection by pathogen or their toxic products .

The antibodies are produced by body to fight the infection .

Once the antibodies develops the person is immune to further infection by the same organism for various period , some time for whole life.

MAY be acquired by :-

i, An attack of disease e.g. Chicken pox , measles.ii, Subclinical infection e.g. Polio , diphtheria.iii, Artificially induced - by Vaccines

B. Passive Immunity When antibodies produced in one person

are transferred to another to give the protection is called “ Passive immunity “ ( Body does not produce its own antibodies).

Passive immunity is short lived and declines in few days or week and disappear

May be acquired in following ways:-

I, Injection antisera e.g. Diphtheria anti toxin for diphtheria.

ii, Injection of Gamma globulins- immunoglobulin's obtained from immune person e.g. measles , hepatitis A.

iii, Maternal antibodies - Through placenta , Milk

Human gamma globulin.

These preparation are of two types.

(i) Human normal immunoglobulin – large pool of human plasma of multiple donors – available as 16.5% solution for subcutaneous / intramuscular use.

(ii) Human specific immunoglobulin - prepared from donors who have been immunized against or recovered from specific diseases .

e.g . Tetanus , rabies , and mumps.

The immunity by GG is passive and temporary.

Antisera or Antitoxin .

These are prepared from animal such as horse , against tetanus , diphtheria, botulism , gas gangrene and snake bite.

In the absence and non availability of human immunoglobulin , antisera are still in preparation and treatment of many diseases.

Precaution must be taken for Anaphylactic shock.

Hypersensitivity

It is an allergy reaction to any foreign substance is introduced in the body. These are Tow types.

(a) Immediate or antibody mediated – eg. Anaphylactic shock.,

(b) Delayed or cell mediated

Anaphylactic reactions are two types – systemic and local.

( SYSTEMIC - eg Penicillin or ATS reaction are immediate with symptoms of Dyspnoea, bronchial spasm , fall of BP, skin rash and occasionally death & best example of LOCAL is Asthma , Urticaria ).

The examples of delayed types are Tuberculin , allergy to fungi , skin graft etc.

Immunizing Agents.

May be classified as Vaccines , Immunoglobulin and Antisera.

VACCINES vaccines are a preparation of disease

agent or its toxic products which are administrated stimulates specific antibodies formation . --- Vaccines induces active immunity.

Vaccines are prepared from :-

(a) Live attenuated organisms e.g. Polio ,

(b) Killed Organisms e.g. cholera , typhoid ,

( c ) A combination of above.

A List of Common Vaccines____________________________________Live attenuated BCG, OPV , Measles Vaccines Yellow fever.______________________________________________________

TyphoidCholeraWhooping

cough.KILLED Vaccines cerebro spinal Meningitis

Plague , Polio (SalK)

rabies , Influenza.______________________________________________________Toxoids Diphtheria , Tetanus.______________________________________________________

Combined ( Mixed) vaccines To simplify administration , reduce cost

and minimize the number of injection more than one immunizing agent may be included in vaccine . These are known as “ combined ‘ vaccine .

Common example of combines vaccine are.:-

i) DPT- diphtheria , whooping cough, (pertussis) and tetanus.

ii) DT – Diphtheria , and tetanus.

iii) Typhoid ( Bivalent),

iv) Indradhanush. Etc.

NATIONAL IMMUNISATION SCHEDULE(a)for infant at birth -BCG and OPV,

hapatitis B(b)At 6 weeks -DPT, OPV, Hap B.(c)At10 weeks - DPT, OPV, Hap B.(d)At 14 weeks - DPT, OPV, Hap B.(e)At 9 months - Measles (f)At 13 – 15 month - MMR.(g)At 16 – 24 month -DPT & OPV (h)At 5-6 years - DT (i) At 10 years -TT(j) At 16 years - TT

(k)For Pregnant women Early in pregnancy - TT 1 or Booster One month after TT1 - TT2

Vaccines must be stored at proper temperature in order to be effective .--- Cold Chain

THE COLD CHAIN Equipment ;

(a) Walk in cold room -- store upto 3 months.

(b) Deep freezers (300 Ltr) / ILR ice lined refrigerator

(c ) small deep freezer / ILR (140Ltr) – for PHC, UHC ( d) Cold Boxes

(e) Vaccine carriers -- for 16 – 20 vials

(f) Day carrier – for 6-8 vials

(i) Ice pack .

PORTAL OF EXIT FOR DISEASE.1, Nose and Throat secretions, eg. TB, diphtheria, mumps, common cold measels

2, Faeces eg. Salmonella, Shigella.Polio ,Hepatitis.

3. Urine eg. S.typhi.

4.Skin eg. Through wound STD agents , Lepra bacilli, scabies etc.

5. Vomit , Body fluid .

General Measures for Control of Infectious Diseases 1. Controlling the Source or Reservoir of

infection.a, early & accurate diagnosis.b, Notification.c, Isolation.d. Surveillancee, Disinfection.

2.Blocking the channels of transmission a, Disinfection of water supply.b. Safe disposal of excreta.c, Control of Insects and Rodents.d, Improving the standard of Food

Hygiene etc.3. Protecting the susceptible population.

a, Immunization – booster dose to have “Herd immunity”.

b, Health Education C, Nutrition

INVESTIGATION OF an EPIDEMIC of UNKNOWN AETIOLOGY.

Epidemics are of Two kinds 1. Progressive - also known as multiple

exposure, repeated or continuous Epidemic. – The disease is all ready in community in endemic form .

2. Point Source epidemic - also known as common or single exposure .

Investigation of an epidemic has four steps.

a, Investigation proper,

b, treatment of Patients.

c, Analysis and interpretation .

d, feedback reporting , and follow up.

INVESTIGATION PROPER.Each patient ,contact

Name , Age , Sex , Occupation and Income.

The Condition of house, sources of water , presence of sanitary latrine , method of disposal of waste.

The source of milk ,meat , fish in case of food poisoning .

The history of visits to pilgrimage ,or any place.

The of bite of insect , rodent , dog or other animal.

The symptoms and signs.

Follow up / revisit to see any change

Sample collection.Depending upon the nature of epidemic ;- Stool.Vomit.Blood.FoodWater Etc.Alcohol

Matched control from neighborhood.

TreatmentPatient is given supportive treatment Isolation at home or in separate wards of Hospital.All persons attending on them or transporting their blood or any specimen are protected .

Analysis and Interpretation About incubation period.General attack rate , specific attack rate by age, sex, economic , occupation and month of year. Etc. Geographic distribution Source of water or milk

While Interpreting .Infectious diseases trend to occur in children.

Milk borne diseases is common in upper income group.

Nutritional deficiency disease is common in rainy season. ( they affect, women and children more ).

All the cases of food poisoning occur together.

An exotic disease first affects the person who had returned from visit out and limited to the contact.

Laboratory investigation will help for chemical or infectious diseases..

The cases do not respond to any antibiotics are likely to be viral