LO: Define and distinguish asepsis, antisepsis, antiseptics, and antibiotics, and explain the difference between antimicrobial prophylaxis and treatment

Healthcare-associated infections

• Pneumonia
• Cather UTI
• Catheter infection
• Surgical site infection

Asepsis and antisepsis

• Asepsis - prevent contamination by microorganisms
• Antisepsis - use of chemical agents to inhibit or destroy microorganisms on living tissue
• Antisepsis $\subset$ Asepsis (antisepsis is a component of asepsis)

Antiseptics and antibiotics

LO: Describe and classify surgical site infections

Surgical site infection (SSI)

• Infection of surgical incision or tissues/organs being operated on due to surgery
• Likely staphylococcus aureus (MRSA)
• SSI increases morbidity, length of hospital stay and cost and potential re-operation

LO: Explain the patient, operation and perioperative factors that influence whether surgical site infection develops

SSI risk

Surgical wound classification

• 1 - low risk
• 4 - high risk

1. Clean: no entry to respiratory, gastrointestinal (GI) or genitourinary (GU) tracts; no infection/inflammation
2. Clean-contaminated: controlled entry into respiratory, GI or GU tracts without unusual contamination
3. Contaminated: major break in sterile technique; GI spillage; traumatic wounds over 12 hours old
4. Dirty/infected: existing infection or gross contamination

Prostheses

• Increase SSI risk and severity
• Foreign material
• Bacteria attach to surface to form biofilm
• Infection of prosthetic material is harder to treat

Biofilm

• Bacteria attach to prosthetic surface
• Secrete slimy extracellular matrix to form biofilm
• Protects bacteria from antibiotics and immune system
• High metabolic activity at the periphery
• Low metabolic activity in the core
• Many antibiotics work best on actively growing bacteria

Inactive bacteria

• Antibiotics block cross-linking of peptidoglycan in bacteria cell wall
• Important when bacteria are actively growing and building new cell wall
• Slow-growing/dormant bacteria affected less

Prevention of biofilms

• Antibiotic-impregnation - incorporate antibiotics into prosthesis
• Anti-adhesive surface - spiky surface to reduce adhesion

LO: Outline the principles of measures to prevent surgical site infection, including appropriate antimicrobial prophylaxis and, where relevant, preoperative MRSA screening and decolonisation of carriers

Prevention

Before surgery

• Optimise patient
• Screen for MRSA and decolonise carriers
• Keep preoperative stay short
• Plan appropriate antibiotic prophylaxis

During surgery

• Asepsis: hand hygiene, PPE, sterilised equipment
• Skin antisepsis
• Antibiotic prophylaxis at right time
• Maintain patient temperature
• Appropriate theatre ventilation
• Good surgical technique - avoid long operations

After surgery

• Wound care/monitoring
• Early recognition
• Treatment of infection
• Review antibiotics given
• Surveillance of SSI rates to identify problems

Thermal homeostasis

• Low body temperature $\to$ vasoconstriction, undermining wound healing and reducing access of cellular/humoural immunity

Theatre ventilation

Antibiotic prophylaxis

• Which drug and when
• Clean-contaminated surgery
• Contaminated surgery
• Dirty/infected urgery
• Clean surgery when prosthesis inserted
• Not for clean, non-prosthetic, uncomplicated surgery

Choice of agent

• Local guidelines
• Takes into account whether the agent will reach the surgical site and cover the likely organisms
• Patient-specific factors may require different choice

Timing and re-dosing

• One IV dose within an hour before surgery, so concentration is high when surgery begins
• Usually no further doses are needed unless surgery is prolonged or blood loss exceeds 1.5 litres

MRSA

• MRSA colonisation is associated with higher risk and severity of SSI
• Particularly true of operations involving prosthesis insertion
• Antibiotics used to treat MRSA are more toxic and less effective than flucloxacilin
• Screen before relevant surgery and attempt MRSA decolonisation

Preoperative MRSA screening

• Swab nose, axilla and groin
• Common Staphylococcus aureus sites

MRSA decolonisation

• Nasal - mupirocin 2% nasal ointment applied inside both nostrils 3 times a day for 5 days
• Skin - Daily bathing or showering with chlorhexidine 4% or octenisan antiseptic soap for 5 days
• Personal hygiene - change towels, flannels, clothes and bedding daily during treatment to reduce re-colonisation risk
• Rescreening - repeat swabs at least 2 days after completing treatment

Limits

• Not always successful
• Antibiotic-resistant organisms means it is not possible
• Once colonised patients assumed to remain colonised indefinitely

LO: Explain the principles of antimicrobial stewardship, including how antimicrobial susceptibility testing (e.g. disc diffusion, minimum inhibitory concentration) and resistance surveillance inform appropriate antimicrobial use

Antimicrobial resistance

• Necessitates use of less effective and more toxic antibiotics
• Could lead to no effective antibiotics
• Undermines treatment of infection
• Increased cost, morbidity and mortality

Susceptibility testing

Disc diffusion

• Pure culture spread evenly over agar plate
• Paper discs with set amounts of different antibiotics placed on surface
• Antibiotic diffuses into agar creating a concentration gradient around disc
• After incubation a clear zone of inhibition forms where growth is prevented
• Zone diameter is compared with standard breakpoints
• Larger zone = more susceptible to that antibiotic
• Zone sizes cannot be compared between different antibiotics

Minimum inhibitory concentration (MIC)

• Lowest concentration of an antibiotic that prevents visible growth after incubation
• Measured by serial dilution or with gradient strips

Reading results

Resistance surveillance

• Ongoing, systematic collection and analysis of resistance data
• Informs empirical prescribing and prophylaxis guidelines
• Detects outbreaks and emerging resistance early so infection control can act
• Allows stewardship interventions to be evaluated

Antimicrobial stewardship

• Effective treatment for patients today, while preserving antibiotics for the future
• Only use antibiotics when needed
• Use the right antibiotic
• Stop the course as soon as possible
• Susceptibility testing and resistance surveillance make these decisions possible

In practice

• Start smart
  • Take cultures before starting antibiotics
  • Prescribe only if there is evidence of bacterial infection
  • Document the indication, drug, dose, route and a review or stop date
• Focus
  • Stop: no evidence of bacterial infection
  • Switch IV to oral when criteria met
  • Change: narrow according to culture and susceptibility results
  • Continue: document the duration and review date
  • OPAT: outpatient parenteral antibiotic therapy

Tackling antimicrobial resistance

• Stewardship
• Infection prevention and control
• Rapid diagnostics
• New antibiotics
• Vaccination
• One health