Epidemiology

- Science that study the patterns of health and disease, its occurrence and distribution for the prevention of disease

Patterns of Disease Occurrence

1. Sporadic - Intermittent

2. Endemic - continuous occurrence

3. Epidemic - sudden inc in no. of cases in a short prd of time - outbreak

4. Pandemic - worldwide occurrence (e.g. SARS)

Communicable Disease

dse caused by an infectious agent acquired from an infected individual transmitted to a susceptible host either by direct or indirect contact or by direct inoculation in the broken skin

Two types of Communicable Dse

1. Infectious

- not easily transmitted from one person to another

- malaria, tetanus, dengue

2. Contagious

- easily transmitted form one person to another

- TB, diphtheria, measles

Infection

The implantation and successful replication of an organism in the tissue of the host resulting to signs and symptoms as well as immunologic response

Virulence

Ability of the microorganism to produce a disease

Pathogenecity

Virulence and potency of the microorganism

True Pathogen

Causes disease or infection in a healthy individual

Opportunistic Pathogen

Causes disease only in susceptible individuals

Carrier

A person or animal that harbors a specific infectious agent and serves as a potential source of infection, yet does not manifest any clinical signs and symptoms of the disease

Asepsis

Freedom from disease causing microorganisms

Medical Asepsis

Includes all practices intended to confine a specific microorganism to a specific area, limiting the number, growth and transmission of microorganisms.

Objects are referred to as clean or dirty

Surgical Asepsis

Practices that keep an area or object free of all microorganism.

Normal Body Defense

Non-specific Defense

Protect the person against all microorganism regardless of prior exposure

Includes anatomic and physiologic barriers and the inflammatory response e.g. skin, nasal passages, saliva, tears

Inflammation

Local and non specific defensive response of the tissues to injury

Manifestations of Inflammation

1. Pain/Dolor

2. Redness/Rubor

3. Swelling/Tumor

4. Heat/Calor

5. Impairment of Function/Functionlysa

Stages of Inflammation

1. Vascular and cellular responses

Constriction of blood vessels on the site of injury

followed by rapid dilatation of small blood vessels(hyperemia)

responsible for heat and redness

Vascular permeability increases

Releases of chemical mediators(bradykinin, prostaglandin, serotonin, substance P, Histamine)

Outpouring of fluids, proteins and leukocytes into interstitial space(swelling)

Pain is caused by the stretching of nerve endings

Blood flow slows

Margination – leukocytes line up along inner surface of blood vessel

Emigration – leukocytes move through the vessel wall of the affected area

2. Exudate production

Exudate is produced

Fibrinogen, thromboplastin and platelets form a barrier(walling off)

Major types of exudates

Serous

Purulent

Hemorrhagic(sanguineous)

3. Reparative Phase

Regeneration – replacement of destroyed tissue by similar tissue

Granulation tissue Formation

Granulation tissue shrinks(Remodelling)

Fibrous (Scar) tissue is formed

Specific Defense

Involves the immune system

Immunity

ability to resist a specific disease

immunization: process of rendering an individual resistant to a specific disease

Types of Immunity

1. Natural

a. Passive – maternal Ab-placental transmission (IgG), breast feeding (IgA) - toxoids

b. Active – exposure and experience

2. Artificial

a. Passive – antibodies

other Ab sources, quick to come, quick to go

b. Active – induction of Ag - stimulate to Ab production (eg: vaccines)

Own and slow to come, slow to go

3. Sub Clinical – an immunity acquired through constant exposure to a particular disease or organism

Two components of the immune system

1. Antibody mediated defenses/humoral immunity

B lymphocytes

Produce antibodies or immunoglobulins

Can Be ACTIVE or PASSIVE

2. Cell mediated defenses/cellular immunity

T lymphocytes

Helper T cells

Cytotoxic Tcells

Suppressor Tcells

Normal blood cells

1. Red Blood Cells(Erythrocytes)

2. White Blood Cells(Leukocytes)

A. Granular

A. Neutrophils

B. Eosinophils

C. Basophils

B. Agranular

A. Lymphocytes

A. T-lymphocytes

B. B-lymphocytes

B. Monocytes

3. Platelets

Reservoir (source)

Portal of Exit

Method of Transmission

Portal of Entry to the Susceptible

Host

Susceptible Host

Etiologic Agent

Chain of Infection

Etiologic agent

Depends on the number, Pathogenecity, ability to enter the body, susceptibility of the host, and the ability of the microorganism to live in the host’s body

Types of Microorganisms Causing Infection

1. Bacteria – a simple one celled microbe with double cell membrane that protect them from harm. Classified according to:

a. Shape – cocci, bacilli, sprilli

b. Need for oxygen – aerobic or anaerobic

c. Response to staining – gram (+) or (-)

d. Motility – Motile or non motile

e. Tendency to capsulate – encapsulated or non encapsulated

f. Capacity to form spores – spore forming or non sporeforming

2. Spirochete – bacteria with flexible, slender, undulating spiral rods that has a cell wall. 3 types of spirochetes include

a. Treponema

b. Leptospira

c. Borilia

3. Viruses – smallest known microbe. Cant replicate so they invade the hosts’ cells and stimulate it for reproduction

4. Rickettsia – small, gram (-) bacteria like microbe that induce life threatening infections. Like viruses they invade hosts’ cells for reproduction. Transmitted through arthropods like lice, fleas, ticks as well as waste products. E.g. Rocky mountain spotted fever, typhus fever and q fever

5. Chlamydia – smaller than rickettsia, common cause of infection in urethra, bladder, fallopian tubes and prostate glands. Transmitted commonly through sexual contact.

6. Fungi – found anywhere on earth. Can be harmful or beneficial.

7. Protozoa – larger than bacteria. Simplest one celled organism of animal kingdom

8. Parasites – live within other organisms. Don’t kill their hosts but take only nutrients

Reservoir

Sources of the microorganism

environment

humans:

frank cases

subclinically-infected

carrier

Incubatory Carrier

Those who is incubating the illness

Convalescent carrier

Recovery stage of illness but continue to shed the pathogenic organism

Intermittent carrier

Occasionally sheds the pathogenic organism

Chronic/ sustained Carrier

Always has infectious organism in his system

animals: dog, cat, cow, chicken

plants

soil

fomites: inedible objects

Portal of Exit from the reservoir

a. Respiratory

b. GIT

c. GUT

d. Wounds and lesions

e. Mechanical escape

incision and drainage

needle aspiration

bites and stings of insects

f. Placenta

Methods of Transmission

weakest link

Direct/contact transmission

Involves direct contact such as touching, kissing, biting and sexual intercourse

Indirect transmission

Vehicle borne transmission

Vector borne transmission

Airborne Transmission

Involves droplets or dust

> 3 ft or 1 meter

Portal of Entry to the Susceptible Host

Microorganisms enter the host the same way they have left the source

a. Respiratory

b. GIT

c. GUT

d. Skin

e. Blood

f. placenta

Susceptible Host

Any person who is at risk of infection

Compromised Host

A person more likely than others to have an infection

Have an “increased risk”

Risk Factors for Infection

Age

Sex

Heredity/genetic predisposition

Level of stress

Nutritional status

Current medical therapy

Preexisting diseases process

Fitness

Environment factors

Absence of or abnormal antibodies or immunoglobulin

Stages of Infection Process

1. Incubation Period

time interval from the 1st exposure to the disease to the appearance of the 1st signs and symptoms

2. Prodromal

time interval from the appearance of 1st s/s to the appearance of the characteristic symptoms of the dse

3. Illness

characteristic symptoms of the dse are manifested

4. Convalescence

gradually s/s will disappear

Nosocomial infections

infections that are associated with the delivery of healthcare services in a health care facility

Iatrogenic Infections

direct result of diagnostic or therapeutic infection

Cross infection

an infection of a new type, usually carried from one patient to another by a break in aseptic technique

Isolation

The separation of an individual suffering from a communicable disease from other persons

Done to confine the infectious agent to a circumscribed area and to prevent its escape from that area

Isolation precautions accdg to CDC(HICPAC)

1. Standard precautions2. Transmission Based Precautions

a. Airborne Precautionsb. Droplet Precautionsc. Contact Precautions

Categories recommended in Isolation

1. Strict Isolation

Prevent highly contagious or virulent infections

i. Wash hands before and after contact with patient

ii. Contaminated articles should be properly disposed

iii. Use of private room

iv. Use of mask

v. Use of gown

vi. Use of gloves

vii. Negative pressure surrounding area is desirable

2. Contact Isolation

close or direct contact precautions

3. Respiratory Isolation

Over short distances through air

4. TB Isolation

For TB patients

5. Enteric Isolation

For direct contact with feces

6. Drainage/secretion precaution

For direct/indirect contact withpurulent materials/drainage from an infected site

7. Universal Precaution

Blood and Fluid precaution

8. Reverse Isolation

For immunocompromised patients

Body substance Isolation

Employs generic infection control for all clients except those with the few diseases transmitted through air

Based on 3 premiseso All people have an increased risk for infection from

microorganisms placed on their mucous membranes and non intact skin

o All people are likely to have potentially infectious

microorganisms in all their moist body sites and substanceso An unknown portion of clients and health care workers will

always be colonized or infected with potentially infectious microorganisms in their blood and other moist body sites and substances