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