Infection & Epidemiology

Infection

The occurrence of microbial or parasitic reproduction on/in a body’s tissues

Pathogenicity

Capacity of a microbe to cause disease

Virulence

The degree to which a microorganism causes pathology

Resident flora

Microorganisms that normally live on or in the human body without causing disease under normal conditions.

• Skin, Mouth, Nose, GI tract

🛡 Protect against pathogens by competing for nutrients and attachment sites

🧪 Some produce substances that inhibit harmful microorganisms

When they enter an unusual body site or if the person's defences are weakened.

When does an opportunistic infection occurs

Antiseptic

Type of chemical disinfectant that is suitable for skin and living tissues

It kills and removes harmful microorganisms without damaging the tissue

Biocidal agent

An agent that is capable of killing microorganisms

Decontamination

The removal of possibly harmful microorganisms from an object by cleaning or disinfecting

Disinfectant

A chemical substance normally used for disinfection of inanimate objects

Pasteurisation

A method developed to preserve milk and other liquids without altering their taste or quality.

Sanitisation

Thorough cleaning of an object or utensil to remove most microorganisms.

Endospores

highly resistant, dormant structures formed inside certain bacteria to help them survive harsh environmental conditions.

Sterilisation

The complete destruction or removal of all microorganisms, including endospores.

Disinfection

Reducing the number of microorganims to an acceptable level

Heat, Incineration, Radiation

The 3 heat strerilisation techniques

Filtration of air and fluids

What is mechanical sterilisation

Use of acids, oxides, and peroxides to sterilise equipment that cannot tolerate heat

What is chemical sterilisation

Thermal death point

The lowest temperature that kills all microbes in 10 mins

Thermal death time

Minimum time to kill all microbes in a liquid at a given temperature

Moist heat

Uses steam or hot water to destroy microorganisms, primarily by denaturing their proteins

• e.g. autoclave

Autoclave

Uses steam under pressure.

The combination of:

🔥 Heat + 💨 Steam + ⬆ Pressure

allows the steam to reach temperatures high enough to destroy microorganisms, including bacterial endospores.

Dry heat

Dry heat is less efficient at transferring heat than moist heat.

So it generally requires: Higher temperature + longer exposure time

180 degrees for 60 minutes

Ethylene oxide

Useful for sensitive materials like rubber

It inactivates proteins

A pregnant person shouldnt use this because it is a reproductive hazard. It damages DNA, harms reproductive health and poses risk to a developing fetus

70% Ethanol or Isopropanol

• Denatures proteins and dissolves bacterial cell wall and membrane

Antiseptics/ Skin Disinfectants

This can be used on skin, mucous membranes, and exposed tissue

e.g. Triclosan & Chlorhexidine

Povidone-iodine

• The yellow color seen on surgical wounds

• A very effective antimicrobial agent

• Used pre-operatively before surgical incision

• Kills a wide variety of microorganisms including endospores

Epidemiology

Study of the origins, spread, and control of disease

Aetiology

Study of what caused the disease

Severe Acute Respiratory Syndrome (SARS)

a viral respiratory disease caused by SARS-CoV, a type of coronavirus.

Morbidity

The number of individuals who are unhealthy due to a specific disease

Mortality

The number of deaths caused by a disease in the whole population

Incidence

Number of new cases of disease in a population during a specific period-expressed as person-time units

Indicates whether cases are increasing or decreasing

Prevalance

Total number of people infected with the disease at any one time. Can indicate duration of disease. EXISTING CASES

Increases as new cases added to the existing case.

Decreases as people are cured or die

Prevalence= Incidence x Duration

Sporadic

occurs occasionally and irregularly

Endemic

Consistently present in a particular population or region.

e.g.Malaria, Chicken pox, Measles

Epidemic

Sudden lcalised rise in disease incidence

Pandemic

An epidemic that spreads across multiple countries/continents and affects large populations

Incubation, Prodromal, Illness, Decline, Convalescence

The distinct periods of disease

Incubation

The period of disease wherein time between exposure to the pathogen and first symptoms shows

Prodromal

The period of disease where early, vague symptoms begin to show which includes feelings of fatigue, headache, and appetite loss

Illness

The period of disease where characteristics or severe symptoms are present

Decline

The period of disease where symptoms decrease

Convalascence

The period of disease where patient recovers and returns toward normal health

Chronic infection

Occurs when recovery is incomplete and mild clinical symptoms persist with occasional acute flare-ups

Septicemia

Infection in the blood

Acute infection spreads to the blood and affects all systems due to lack of host defences

Subclinical infection

an infection where a person is infected with a microorganism but does not develop noticeable symptoms.