Microbiology SC038: Antibiotic Prophylaxis: Is It Really Necessary? Flashcards
Prophylactic antibiotics in surgery
Purpose:
1. Prevent / Reduce surgical wound / site infection
- infective organisms usually from skin / mucosal commensal flora
Risks:
1. Toxic / allergic reactions
2. Emergence of resistant bacteria
3. Superinfection
Prophylactic antibiotics indicated in:
1. Procedures associated with high risk of infection (clean-contaminated / contaminated)
2. Procedures involving implantation of prosthetic material
3. Some procedures when infections are especially serious (e.g. when patient is immunocompromised)
Choice of antibiotic
Factors to consider:
1. Likely organism
2. Susceptible antibiotic
Principles:
- Drugs for prophylaxis should NOT be 1st-line drugs for treatment ∵ may compromise their effectiveness in treatment
- Use agents with ***narrow spectrum: usually mean 1st / 2nd generation cephalosporin (GC)
- Use agents with proven safety profile
- Avoid use 3rd GC, fluoroquinolone (many SE) & carbapenem (unless no other options)
Cefazolin:
- Single dose 1g IV **Cefazolin (1st gen cephalosporin) is appropriate for most procedures
- High blood + tissue level —> well above MIC of susceptible organisms (e.g. E. coli, S. aureus, Streptococci)
- Adequate cover for common bacteria causing surgical infections
- t1/2 (2 hours) > other 1st gen cephalosporin
- Last **>4 hours (duration of operation is within duration of action where MIC well above pathogens)
- Proven efficacy for >15 yrs
- Good safety profile
Vancomycin:
- Avoid routine use of vancomycin —> Promote emergence of VRE
- Indications for vancomycin
—> Serious allergy to penicillin / cephalosporins
—> Institutions with high incidence of postoperative MRSA infection
- Colorectal surgery / appendectomy:
—> **Cefoxitin / **Cefotetan (instead of Cefazolin ∵ need coverage for anaerobes / Cefazolin-resistant gram -ve bacteria)
—> Alternative **Cefuroxime (cover for gram -ve bacteria) + **Metronidazole (cover for anaerobes)
When to give
- Given within ***30 mins before first surgical incision —> During induction of anesthesia
- Don’t give it during going to OT —> interval to skin incision is often longer than 2h
Need for 2nd dose
Reasons:
- Tissue level slightly lower than blood level
- Blood loss during OT (speed up loss of antibiotic)
Recommendations:
- Re-dosing (i.e. 2nd dose, intra-operative) NOT necessary for most procedures, unless duration of OT is long
- Recommended re-dosing interval depends on half-life of the given antibiotic —> ***2 times the t1/2 (re-dosing of cefazolin is recommended at 4h, if surgery longer than that)
Overuse of prophylactic antibiotic
- Longer is NOT better + Not more effective
- ***No indications / evidence for postoperative antibiotics (although commonly done)
- Documented that it lead to problems:
—> Increase risk of SE
—> Increase risk of infections (e.g. Pseudomembranous colitis, line sepsis, pneumonia (∵ modify oropharyngeal flora —> more pathogenic pattern of colonisation)
Prophylactic use of antibiotic in Family practice setting
Indications:
Non-surgical, common situations:
1. Rheumatic fever
2. Meningococcal disease
3. Recurrent UTI in women
4. Human / Animal bite
- Prevention of Rheumatic fever
Primary prevention (prevention of initial attacks of rheumatic fever)
- Acute rheumatic fever is rare in HK now
- **Appropriate treatment of group A streptococcal (GAS) pharyngitis prevent acute rheumatic fever in most cases
- GAS pharyngitis is a **microbiological diagnosis
- Patient with confirmed GAS pharyngitis should be treated for an entire ***10-day period, even though they will likely be asymptomatic after the first few days
Treatment of GAS pharyngitis:
- No advantage with broad spectrum penicillins (e.g. Ampicillin / Amoxycillin) or Cephalosporins
- **Single dose of IM / **10 days Oral Benzathine penicillin for patients who are unlikely to complete a 10-day course of oral therapy
- ***10 days Oral Erythromycin is acceptable for patients
allergic to penicillin (although high resistance to macrolide in HK —> Tetracycline / Fluoroquinolone)
- Post-treatment throat cultures NOT required, except
—> Recurring symptoms
—> History of rheumatic fever
Secondary prevention (preventing recurrent acute rheumatic fever by prevention of GAS reinfection):
- An individual with a previous attack of rheumatic fever in whom GAS pharyngitis develops is at high risk for a recurrent attack of rheumatic fever
- A GAS infection need not be symptomatic to trigger a recurrence —> hence “recognition + treatment” is insufficient
- ***Continuous antimicrobial prophylaxis with a narrow spectrum penicillin
Indication:
- Previous acute rheumatic fever
Choice of agent:
- **Monthly IM Benzathine penicillin
- Alternatives: **Oral Penicillin V / Erythromycin BD
Timing:
- Initiate penicillin once acute rheumatic fever / chronic rheumatic heart disease is diagnosed
- Start with a ***10-day course of treatment to eradicate carriage
Duration:
Individualized depending on each patient situation:
- Risk increases with **multiple previous attacks
- Risk decreases as **time interval since the most recent attack lengthens
- Likelihood of acquiring GAS pharyngitis (via droplets) —> increased exposure in children, adolescents, parents of young children, teachers, physicians, nurses, personnel in contact with children, military recruits
- Consequence of recurrence (e.g. history of Rheumatic ***carditis)
Rheumatic fever with carditis + Residual heart disease:
- ***10 years / Until 40 yo (whichever is longer), sometimes lifelong
Rheumatic fever with carditis + No residual heart disease (no valvular disease):
- ***10 years / Until 21 yo (whichever is longer)
Rheumatic fever without carditis:
- ***5 years / Until 21 yo (whichever is longer)
Diagnostic criteria of Rheumatic fever
JONES CAFE PAL
Major criteria (JONES):
1. Joint involvement
2. Myocarditis (O look like a heart)
3. Nodules, SC
4. Erythema marginatum
5. Sydenham chorea
Minor criteria (CAFE PAL):
1. CRP increased
2. Arthralgia
3. Fever
4. Elevated ESR
5. Prolonged PR interval
6. Anamnesis (History) of Rheumatism
7. Leukocytosis
Diagnosis:
Throat cultures growing GAS / Elevated Anti-streptolysin O
+
2 major / 1 major + 2 minor
- Prevention of meningococcal meningitis
Signs:
- Purpura / Petechiae (indicate underlying DIC) —> Medical emergency
Spread:
Droplet from patient with meningitis
—> Colonisation in Nasopharynx (Carriage of bacteria)
—> Invade circulation
—> Meningococcaemia
—> Meningitis
Post-exposure prophylaxis (PEP):
- Elimination of bacterial carriage in ***nasopharynx by identify close contacts of patient with meningitis
- To prevent secondary cases (sporadic case, attack rate ~0.4% among close contacts)
Indications:
- **Household + Other intimate (e.g. close contact >4h in the week before onset, kissing) contacts of patients with documented meningococcal disease
- Medical personnel with **unprotected, direct contact with oral secretions (e.g. mouth‐to‐mouth resuscitation, intubation)
Management:
- Start prophylaxis **ASAP, **<24h (interval between exposure to onset of disease can be **very brief)
- **Single dose **Oral Ciprofloxacin / **IM Ceftriaxone (if CI to Ciprofloxacin e.g. children / pregnancy)
- ***Vaccine can also be considered (if serotype of organism known) —> but takes time to develop Ab (usually done at 1-2 weeks after antibiotic prophylaxis)
- Human / Animal bite
Risk of infection:
- Human >70% (e.g. in fist fight)
- Cat bite 50%
- Dog <10%
- Rodent 2% (depth of penetration limited + dose small)
Management:
1. Wound Irrigation
- ***Povidone-iodine
- important to disinfect wound tunnel (instead of skin surface only)
- after adequate anesthesia, infected animal bite is opened + thoroughly irrigated using a 30 ml syringe + commercial splash shield
- even with attached splash shield, there can be significant splatter and potential for body fluid exposure
- appropriate precautions should be followed at all times
- Wound Soaking
- for exposed part of wound
- soaking is an appropriate method for loosening debris and coagulated blood but is NOT a substitute for irrigation
Mammals bite wound (Dogs and Cats):
1. Clean + copiously irrigate with normal saline / povidone-iodine solution with a syringe
2. Explore for possible tendon or bone involvement + foreign bodies
3. May be closed if cosmetically desirable
4. Immunisation: **Tetanus, **Rabies
5. Antibiotic prophylaxis – if high risk wound and in certain patient groups (e.g. splenectomy)
Tetanus wound management
Tetanus-prone wounds:
- Contaminated with dirt, faeces, saliva
- Punctures
- Burns
- Crush injuries
- Injuries with necrotic tissue
> =3 doses of vaccination history:
- No need for prophylaxis
Unknown / <3 doses of vaccination history:
- Clean, minor wounds: Td (Tetanus and diphtheria toxoids), No need for TIG (Tetanus IG (i.e. booster))
- All other wounds: Td + TIG
Rabies (From HNS11)
Long incubation period: usually 20-90 days, can be >1 year
Prodromal: non-specific, onset of itching at site of healed bite wound
2 presentations:
1. Furious rabies (typical): hydrophobia (spasm of swallowing reflex), aerophobia, meningo-encephalitis
2. Paralytic rabies: paralysis begins in bitten limb and spreads, may be confused with myelitis / encephalitis due to other causes
—> Both invariably fatal
Laboratory diagnosis —> demonstration of virus:
1. Brain (Viral inclusion bodies / Negri bodies)
2. Skin biopsy (after descending infection)
3. Corneal impression smear
Management:
- No treatment once symptoms appear —> fatal
- Prevention only
Prevention:
1. Management of dog bites
- good wound toilet, aggressive washing of bite to physically wash out virus, use local anaesthesia if needed
- avoid suturing
- manage Tetanus risk (Tetanus vaccine)
- Assess rabies risk (where, what animal, unprovoked, break in skin / mucosal exposure)
- rabies only affect ***mammals (no risk from insects, reptile, bird, fish), domestic rats in HK are NOT infected
- endemic area: no endemic rabies in HK, infection in China / other parts of Asia. is the animal imported? Bite occur overseas?
- behaviour of animal: unprovoked bite? has animal bitten other human/animal? clinical signs of rabies (paralysis, increased salivation) of the animal?
- is animal available for observation? If animal is alive after 7 days —> rabies excluded, animal brain submitted for virology examination —> infection can be diagnosed by looking for viral inclusion bodies (Negri bodies) / virus antigens by IF - Post-exposure prophylaxis
- possible due to long incubation period
- active / passive immunisation (for risk present / high risk present respectively)
- Active immunisation: **Human diploid cell vaccine (killed vaccine), 4 doses give IM to deltoid at days 0, 3, 7, 21 —> immunisation course can be aborted if animal later shown to be NOT infected
- Passive immunisation: **Human rabies immune globulin (HRIG) —> infiltrate bite wounds thoroughly —> inject any reminder IM to thigh (at a site different to vaccine) - Control of source
- control stray dogs
- vaccination of dogs (done in HK) - Pre-exposure prophylaxis
- vaccine for high risk individuals (e.g. vets, long term travel in endemic areas)
Prevention of Rabies
If dogs / cats / ferrels —> Depends (healthy? rabid? provoked attack? available for observation? known origin?)
If wild animals —> PEP
Bite wound microbiology
- Always a mixed infections by aerobes and anaerobes
- Capnocytophaga canimorsus (part of oral flora in cats
/ dogs) —> can cause rapidly fatal infections in patients
without spleen (or immunosuppressed patients)
Dog bites:
Aerobes:
- Pasteurella spp.
- Streptococcus spp.
- Staphylococcus spp.
- Neisseria spp.
Anaerobes:
- Fusobacterium spp.
- Bacteroides spp.
- Porphyromonas spp.
- Prevotella spp.
- Capnocytophaga spp.
Cat bites:
Aerobes:
- Pasteurella spp.
- Streptococcus spp.
- Staphylococcus spp.
- Moraxella spp.
Anaerobes:
- Fusobacterium spp.
- Bacteroides spp.
- Porphyromonas spp.
Bite wound bacterial prophylaxis
Antibiotic prophylaxis, consider if:
- Moderate to severe injury
- Involve bone or joint
- Hand / face bite
- Wound near a prosthetic joint
- Underlying disease (e.g. splenectomy —> OPSI)
- Present >8 hr
Choice of agent:
- need to cover likely pathogen in the oral flora of the biter
- usually either Amoxicillin-clavulanate (Augmentin) or Ampicillin-sulbactam
If CI to Augmentin:
- Combination: **Fluoroquinolone (for other bacteria) + **Clindamycin / ***Metronidazole (for anaerobes)
