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IMS- Strand 7 > How infections happen > Flashcards

How infections happen Flashcards

1
Q

What does the chain of infection involve?

A
  • infectious agent
  • Susceptible host
  • Portal of entry way in
  • Mode of transmission
  • Portal of exit way out
  • Reservoir
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2
Q

What is an infectious agent?

A

This is the microorganism (germ or bug) that can cause harmful infections and make you ill.

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3
Q

What is a reservoir?

A

This is where the germ lives and grows

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4
Q

Portal of exit way out

A

The germ then needs to find a way out of the infected person so it can spread

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5
Q

Mode of transmission

A

Once the germ is out it can spread from one person to another by hands or on equipment such as a commode, in the air by coughing or contact with body fluids and blood

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6
Q

What is the portal of entry way in

A

The germ then needs to find a way into another person

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7
Q

What is a susceptible host?

A

This is a person who is at risk of infection because they are unable to fight the infection

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8
Q

Host- parasite relationship

A
  • Parasites are organisms which have a relationship with a host (live in or on the host), in which the parasite benefits and the host is harmed
  • An obligate parasite is a parasite that depends on a host for nourishment, reproduction, habitat and survival. It will not be able to survive away from the host e.g. Head louse
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9
Q

What is the definitive host?

A

the host where sexual reproduction occurs

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10
Q

What is the accidental host?

A

Accidental host is the host in which parasite does not normally develop but when infections occur, the parasite is able to complete its life cycle

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11
Q

What is the intermediate host?

A

Intermediate host is the host required in the life cycle of the parasite but either no reproduction occurs here, or asexual reproduction occurs

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12
Q

What are communicable diseases?

A
  • Communicable diseases are diseases due to an infectious agent or its toxic products that is capable of spreading from one person to another, from an animal to a person or from the environment to a person
  • E.G. COVID-19 , Ebola
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13
Q

Susceptible

A

Susceptible individuals are at risk of illness if they interact with infectious individuals

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14
Q

Recovered

A

After recovery, individuals may experience infection- conferred immunity for a period of time

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15
Q

Exposed

A

Exposed individuals have interacted with infectious individuals and are infected but not yet infectious

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16
Q

Infectious

A

Once infectious, individuals may require medical care or experience complications

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17
Q

Colonisation

A

Normal colonising flora on the human body. Do not have pathogenic effect on the host. Prevent harmful bugs from getting it.

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18
Q

Where do infections come from?

A

Endogenous
Exogenous

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19
Q

Endogenous infection (who does it affect)

A
  • Ourselves
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20
Q

Exogenous infection (communicable) (who does it affect)

A
  • person- to- person
  • Non- human sources (animals/ birds/ insects)
  • Environment
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21
Q

Endogenous infection

A

Normal flora
- Skin
- Gut
- Upper airway
- Genital tract
Normal flora gets into wrong place
- Typically translocated to sterile sites

Most mucocutaneous surfaces of humans harbour multiple types of bacteria

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22
Q

Endogenous infection- example

A

Cystitis
Infection of lower urinary tract
- Lower abdominal pain
- Urgency
- Dysuria
- Frequency
Most commonly bacterial from gut flora
- E.g. escherichia coli

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23
Q

Exogenous infection

A
  • Communicable diseases
  • Person to person spread
  • Examples:
    Measles
    Neisseria meningitidis
    HIV
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24
Q

Non- human source examples

A
  • Influenza (reservoir in pigs/ birds)
  • Dengue (spread by Aedes mosquito)
  • Rat bite fever (streptobacillus moniliformis)
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25
Environment examples (soil/water)
- Clostridium tetani (Tetanus) - Cholera - Schistosomiasis
26
Endogenous routes of transmission
- migration - perforation - blood
27
Exogenous routes of transmission
- Contact (direct or indirect) - Injuries (trauma, bites) - Airborne - Oral (food/ water) - Blood borne - Sex - Mother to baby (vertical)
28
Endogenous infection- migration
- Bowel flore e.g. ECOLI contaminates perineum - Gains access to urethra (easier in females) - Causes local infection - Spreads to bladder (cysitis) and beyond - UTI
29
Endogenous infection- Perforation
Diseases of bowel especially colon - Cancer - Diverticular disease Perforation of bowel wall leads to contamination of abdominal cavity with faecal flora Severe life- threatening infection results - Peritonitis
30
Endogenous infection- blood spread
Endocarditis - Dental work may allow normal mouth flora e.g. streptococci to enter the blood stream - Circulation of organisms allows them to reach distant sites e.g. heart valve - Invasion can occur especially if valve tissue is abnormal e.g. congenital defect
31
Exogenous infection- Direct contact
Herpes simplex - Viral infection of skin which causes cold sores and genital herpes spreads via direct skin to skin contact
32
Exogenous infection- Indirect contact
- Micro organisms can be transmitted indirectly via hands, equipment, furniture etc - Major route of health- care associated infections Examples - Methicillin- resistant staphylococcus aureus (MRSA) - Clostridium difficile - Norovirus gastroenteritis
33
Injuries- dirty wounds
Tetanus Clostridium tetani - Bacterium present in soil - Contaminates wounds - Releases toxin causing muscle spasm - Prevented by vaccination
34
Bites
Malaria - Parasitic infection (plasmodium species) - Life cycle - Present in large areas of tropics Rabies - Viral infection - Spread via bite of infected animals
35
Airborne infection
COVID- 19 Influenza Rhinovirus - Coughing & sneezing - Droplets formed containing infectious viruses - Inhaled by others
36
Foodborne infections
- Food prepared with poor hygiene or undercooked food - Contaminated food not cooked at high enough temp to kill pathogens - Result= food poisoning
37
Sexually transmitted infection
E.G. Chlamydia- risks increased by: - Unprotected sex - New partners - Multiple partners - Partners with higher risk of STIs e.g. commercial sex workers
38
Blood borne infections
e.g. Hep C virus - Liver infection - Some viruses spill into blood (and other body fluids) Transmission by blood exposure - Transfusion - Sharing of needles etc - Tattoos and body piercing
39
Vertical transmission
Mother to baby transmission "vertical" - Antepartum (during pregnancy) e.g. rubella - Peripartum (at time of birth) e.g. herpes simplex - Postpartum (during deliver) e.g. HIV via breastmilk when mother is uncontrolled
40
Some infections may be transmitted in more than one way e.g. HIV
- Blood borne e.g. injecting drug use - Vertical (antenatal, perinatal, breast feeding) - Sexual
41
Some infections require more than one step e.g. Staphylococcus aureus soft tissue infection
- Step 1: Colonisation of skin- joins skin flora - Step 2: penetration of skin- spreads & damages
42
What are HCAIs?
Healthcare associated infections are infections that occur while receiving health care, developed in a hospital or other health care facility that first appear 48 hours or more after hospital admission, or within 30 days after having received health care
43
Surgical site/ breaks in skin
Contamination of surgical wounds or breaks in skin barrier can lead to infection from normal skin flora
44
Implant associated surgery
Procedures, such as hip replacements can lead to infection and septicaemia
45
Mucosal surfaces
Eyes, mouth, nose can act as portals for microbial transmission
46
Ventilators
Indwelling devices, such as ventilators, can cause HCAI such as pneumonia
47
Catheters
Use of intravenous or urinary catheters can cause urinary tract infection (UTI) and septicaemia
48
7 strategies to prevent healthcare- associated infections
- Hand hygiene - Environmental hygiene - Screening and cohorting patients - Surveillance - Antibiotic stewardship - Following guidelines - Safety culture
49
Pathogen factors in infection
- Infectious dose - Virulence factors & toxins - Resistance to antimicrobials
50
Infectious dose
- Minimum number of organisms required to produce disease
51
Virulence factors
- Allow invasion of host tissues - E.g. streptolysin O Lyses cells- cytolysin Produced by certain streptococci (Group A)
52
Cholera (toxins)
- Severe watery diarrhoea- "rice water" - Bacteria produce toxin - Binds to gut lining cells (mucosa) - Secretory diarrhoea - Massive loss of fluid and electrolytes - Causes severe dehydration, kidney failure & death
53
Antimicrobial resistance
- Micro- organisms readily mutate e.g. HIV, straphylococci - Mutations happen normally- may be advantageous, deleterious or neutral - More antibiotic use= more chance that an advantageous mutation will happen in the presence of antimicrobial and be sustained - Failure of antimicrobial treatment
54
Host factors in infection
- Environment - Barriers to infection - Genetics
55
Environment (host factor)
- Geography - Climate - Financial (availability of health care e.g. vaccination) - Public health infrastructure (sanitation) - Distribution of other infection hosts (insects or other vectors)
56
Dengue fever
- Viral infection - Transmitted by Aedes mosquito - Fever & rash & muscle pain Severe form: bleeding, shock & multi organ failure
57
Barriers to infection (host factor)
- Skin & mucous membranes - Stomach acid - Native bacteria - Immune system problems (primary & secondary) - Behaviour
58
Skin & mucous membranes
Cuts - Entry point for pathogens - Wound infection Corneal abrasions - Entry point for pathogens - Conjunctivitis
59
Gastric/ stomach acid
- Hydrochloric acid= pH 2 - Very few organisms survive this - Commonly used drugs for stomach ulcer increase pH. - Patients taking these are more susceptible to food poisoning - E.g. campylobacter from poorly cooked chicken
60
Native bacteria/ normal flora
Normal gut bacteria - Prevent colonisation by pathogenic (disease- causing) bacteria - Antibiotic treatment destroys the normal "friendly" bacteria - This allows the pathogens (bad bacteria) to cause infection - E.G. diarrhoea due to clostridium difficile
61
Genetics (host factors)- primary immune system
Primary immunodeficiencies Rare >400 known primary immunodeficiencies Common variable immune deficiency Complement deficiencies Genetic variations can protect against infection - Sickle cell disease heterozygotes are protected against malaria
62
Genetics (host factors)- secondary immune system
Acquired immunodeficiency- immune deficiency occurs later in life - Treatments which suppress the immune system e.g. - Cancer - Immune suppression for autoimmune disorders (corticosteroids, ciclosporin, rituximab) HIV (uncontrolled without treatment) - Infects and destroys CD4 immune system cells
63
Behaviour and social history
- Occupation - Travel - Recreation - Sex - Drugs - Contacts (friends or pets)

IMS- Strand 7 (3 decks)

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