Introduction to infection Flashcards
What is infection?
Give some examples of infection
The process of microbial invasion
- common cold
- tonsillitis
- urinary tract infection
- infected leg ulcer
What is infectious disease?
An infection that is readily transmissible
- respiratory infections; TB
- gastrointestinal infections
- sexually transmitted infections (STI)
•Not all infections are ‘infectious’
Describe endogenous Infection
- Infection occurs from within the patient
- Normal bacterial flora may cause infection
Give examples of endogenous infections
- Oral thrush:
Candida albicans
-Catheter-related infections:
Staphylococcus epidermidis
Describe exogenous infection
An infection which originates from outside of the body
Give examples of exogenous infections
(A) Cross Infection- on eperson infects another my touch
- S. aureus / MRSA surgical site infection
(B) Environmental Infection
- Air: Lower respiratory tract infection (air);
Aspergillus fumigatus pneumonia; TB; coronavirus
- Foodborne: bacterial, viral
Infections are generally categorised into:
(a) Community Associated Infections→ aquire during everyday living (e.g. STI’s and the common cold)
(b) Healthcare Associated Infections (present 48 hours or more afterwards suggests it has been acquired from the hospital)
Extent and Cost of Healthcare Associated Infections
- More common in ‘at risk’ patients
- 9% (approx. 300,000) patients PER ANNUM get infected whilst in hospital and primary care (source: NHS England); these patients then become a source of infection
- 11 days extended hospital stay
- 9,000 patients die from HAI each year
- Cost to NHS: £1,000,000,000 per year
Describe healthcare associated infections and risk factors
- Most common HAI are gastrointestional infection (22%)→broad spectrum antibiotic use which kill our normal gut flora (C.difficile)
- Mechanical ventilation→respiratory infections
- Cathetherisation→UTI’s (20%)
- Surgical site infection (14%)
- ChloraPrep (skin antiseptic)→ sits on surface of your skin and allows microorganisms to enter body during surgery
Microorganisms commonly associated with HAI
Infections are spread through the ‘Chain of Infection’
- UTI’s→E.Coli
- Surgical site infections→Staphlococcus aureus and MRSA
- Respiratory infections→ aspergillus fumigatus and Staphlococcus aureus
How Infection is Spread: Describe ‘the Chain of Infection’
Causative agent:
- Bacteria
- Viruses
- Parasites
- Fungi
Resovoir:
- Patients
- Staff
- Environment
- Food / Water
Portal of exit:
- Droplets
- Secretions
- Excretions
Mode of transmission:
indirect contact eg. food / droplets
direct contact eg. touch
Portal of entry (into second host):
- Skin
- GI Tract
- Respiratory Tract
- Bloodstream
- Surgery
- Urinary Tract
Susceptible host:
- Elderly / Infants
- Immunocompromised
- Risk Factors
Introduction to Staphylococcus aureus:
A Leading Cause of HAI
- Family: Staphylococcaceae
- Morphology / Biochemistry:
- Gram-positive cocci / clusters
- facultative anaerobe
- non-sporing
- catalase positive (splits hydrogen peroxide into water and oxygen)
- DNAase positive
- coagulase positive (converts fibrinogen to fibrin) which can surround an protect it
- Carriage: nasal (40%); faecal (20%); skin (10%)
- Spread: droplets / skin scales
- Surgical site / tissue / respiratory / bloodstream infections
Staphylococcus aureus: Pathogenicity (virulence factors):
- Adhesion
- Avoid
- Damage
- Adhesion: MSCRAMMS (microbial surface components recognising adhesion matrix molecules) adhere to fibronectin
- Avoid the host immune response:
microcapsule around its cell wall which stops parts of the complement system, particularly c3b from adhering
protein A bing IgG by the FC portion (wrong way around) so phagocytosis doesnt occur
- Damage the host through production of virulence factors: TSST1 (toxic shock syndrome toxin 1), exfoliative toxin (breaks down dermal junctions in the skin-scalded skin syndrome)
- Causes superficial (surface of skin), deep (in tissues) and systemic infections (in our blood stream); infects several body sites
Sate superficial, deep and systemic sites of S. aureus infection
*
- pneumonia→ lungs
- emesis→ liver
Introduction to MRSA: Methicillin Resistant Staphylococcus Aureus
- 1960: Penicillin resistant S. aureus (beta lactamase)
- 1960: Methicillin produced: withstands beta lactamase
- 1961: MRSA first recognised; 21st century; a major HAI
- Infections in hospital; community; carriers (1%)
- Transmission: Touch; hands or surfaces
Methicillin Resistance in S.aureus: Modification of Target Site
How does this bacterium become resistant to beta-lactamases?*
- Production of MODIFIED target site; PBP (transpeptidase)
- S.aureus produces PBP
(a) cross-links peptide chain (final stage of peptidoglycan formation)
(b) HIGH affinity for beta lactam antibiotics
•MRSA produces PBP2a
(a) cross-links peptide chain
(b) LOW affinity for beta lactam antibiotics
- mecA gene -incorporated into SCCmec: encodes for PBP2a
- SCCmec mobile genetic element - transmissible by conjugation
MRSA infections are difficult to treat and become very serious
Due to limited treatment options (can’t use any beta lactam antibiotic)
MRSA infection in the Healthcare Setting:
state the sypes of superfical and deep infections
- Superficial; surgical site infection,
- Deep; catheter-related infection,
- Deep; tissue infection and
- Deep; post surgical abscess
How can the host’s ability to resist infection be enhanced?
- Influenza vaccine → for the elderly
- Pneumonia vaccine → for immunocompromised
How can be Break the ‘Chain of Infection’?
- Screen, identify, treat, isolate if necessary (single, cohort wards)
- Infected/Susceptible Patient
- Wounds: Keep covered up
- Respiratory: catch it; kill it, bin it
- Personal Protective Equipment (PPE)
- Disinfect surfaces
- Effective hand washing
What is the single most effective method of preventing the spread of infection?
Wash your hands
How do you wash your hands properly?
What two types of organisms are on our hands?
Resident bacteria and transient bacteria
Does effective hand washing remove resident bacteria or transient bacteria?
- Effective hand washing removes TRANSIENT bacteria eg. . MRSA, S.aureus, C. difficile
- 99% of transient bacteria (i.e surface / contaminating bacteria) on your hands are removed by effective handwashing
