SSTI Flashcards
Protecting factors of skin
1) Dry surface
2) Fatty acids –> skin surface is acidic (pH ~5.6)
3) Renewal of epidermis
4) Low temperature (VS core body temperature)
Pathophysiology of SSTIs
Disruption of normal host defenses, leading to:
1) Penetration of normal skin bacteria into deeper layers
2) Introduction of other bacteria into the skin
3) Excess bacterial growth
Risk factors for SSTIs
1) High bacterial innocula
2) Reduced blood supply to skin (e.g. due to peripheral vascular disease)
3) Presence of bacterial nutrients (e.g. glucose in DM patients)
4) Excessive moisture
5) Poor hygiene
6) Sharing of personal items (e.g. towels, razors)
Classification of SSTIs
1) Severity / Extent
2) Depth of infection - Superficial (uncomplicated) VS Deep (complicated)
3) Presence of discharge - Purulent VS Non-purulent
4) Microbiology - Single organism (primary) VS Polymicrobial (secondary)
5) Anatomical site
Types of SSTIs, based on anatomical site
1) Epidermis - Impetigo
2) Dermis - Ecthyma; Erysipelas
3) Hair follicles - Furuncles, Carbuncles
4) Subcutaneous fat - Cellulitis
5) Fascia - Necrotizing fasciitis
6) Muscle - Myositis
Common causative organisms of SSTIs
Most common:
1) Staphylococcus aureus (MSSA)
2) ß-hemolytic Streptococci (e.g. S. pyogenes)
Community-acquired MRSA
1) Prevalence in SG
2) Risk factors
Prevalence: Relatively low (< 30 – 35%)
Risk factors:
1) Critically ill (admission to ICU)
2) Immunosuppression (due to chemotherapy, organ transplant)
3) Failure to respond to antibiotics that do not cover MRSA
SIRS criteria
1) Temperature < 36 degC OR > 38 degC
2) Heart rate > 90 bpm
3) Respiratory rate > 24 bpm
4) WBC > 12 x 10^9/L OR < 4 x 10^9/L
Impetigo & Ecthyma - Classification
1) Severity
2) Depth of infection
3) Presence of discharge
4) Microbiology
5) Anatomical site
1) Usually mild
2) Superficial (uncomplicated)
3) Purulent or non-purulent
4) Single organsim
5) Impetigo - Epidermis; Ecthyma - Up to dermal-epidermal junction
Impetigo & Ecthyma - Clinical presentation
1) May be non-bullous or bullous (fluid filled vesicles)
2) Usually found on face/extremities; More common in children
3) Ecthyma is deeper than impetigo, scarring is common
Impetigo & Ecthyma - Microbiology
1) S. aureus
- Usually causes bullous form
2) ß-hemolytic Streptococci (e.g. S. pyogenes)
Impetigo & Ecthyma - Culture
Usually treated without culture
May culture if pus
Empiric therapy of impetigo (most cases)
1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing
1) MSSA, ß-hemolytic Streptococcus
2) Topical
3) 5 days
Antibiotics:
Mupirocin - Apply to affected area BID
Empiric therapy of impetigo (severe cases)
1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing
1) MSSA, ß-hemolytic Streptococcus
2) Oral
3) 7 days
Antibiotics: Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment needed in renal impairment Clindamycin - PO 300mg QDS - Alternative in penicillin allergy
Empiric therapy of ecthyma
1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing
1) MSSA, ß-hemolytic Streptococcus
2) Oral
3) 7 days
Antibiotics: Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment needed in renal impairment Clindamycin - PO 300 mg QDS - Alternative in penicillin allergy
Culture directed therapy for ecthyma (and severe impetigo)
Duration: 7 days
Causative organism: MSSA
PO Cloxacillin 250-500 mg QDS
PO Cephalexin 250-500 mg QDS
- Dose adjustment needed in renal impairment
Causative organism: S. pyogenes
PO Penicillin VK 250-500 mg QDS
Purulent SSTIs - Types
1) Furuncles
2) Carbuncles
3) Cutaneous abscesses
Purulent SSTIs - Classification
1) Presence of purulence
2) Microbiology
3) Anatomical site
1) Purulent
2) Usually single organism. Large abscesses may be polymicrobial (especially those pre-treated with antibiotics)
3) Furuncles - Hair follicles
Carbuncles - Few adjacent hair follicles
Cutaneous abscesses - Within dermis
Purulent SSTIs - Clinical presentation
Furuncles - Inflammatory nodule
Carbuncles - Forms small abscess; Larger & deeper than furuncles
Cutaneous abscess - Nodule with a rim of erythematous swelling; Pus collection
Purulent SSTIs - Risk factors
1) Close physical contact
2) Crowded living conditions
3) Sharing of personal items
4) Poor personal hygiene
Purulent SSTIs - Microbiology
S. aureus
Purulent SSTIs - Culture
Usually treated without culture
Also reasonable to culture pus
Management of purulent SSTIs
Mainstay treatmetn: Incision & drainage (I&D)
Systemic antibiotics only recommended in certain select situations (adjunctive therapy)
When are adjunctive systematic antibiotics recommended in purulent SSTIs
1) Unable to drain completely
2) Lack of response to I&D
- Wait for a few days before checking response (takes time to improve)
3) Immunosuppressed (e.g. chemotherapy, organ transplant)
4) Extremes of age (very young/old)
5) Extensive disease involving several sites
6) Signs of systemic illness - SIRS criteria
Empiric therapy of purulent SSTIs - Organisms to cover
MSSA
Only cover MRSA if patient has any MRSA risk factor
Empiric therapy of purulent SSTIs - Route
Oral usually adequate
IV only needed for more severely ill patients (require hospital admission)
Empiric therapy of purulent SSTIs - Duration
Outpatient: 5-7 days
Inpatient: 7-14 days
Empiric therapy of purulent SSTIs - Antibiotics & dosing
Not MRSA coverage:
Cloxacillin - PO 250-500 mg QDS
- OR IV 1-2g q4-6h
Cephalexin - PO 250-500 mg QDS
- Dose adjustment needed in renal impairment
Cefazolin - IV 1-2g q8h
- Dose adjustment needed in renal impairment
MRSA coverage: Clindamycin - PO 300 mg QDS - OR IV 600 mg q8h Cotrimoxazole - PO 800/160mg BD - Dose adjustment needed in renal impairment Doxycycline - PO 100 mg BD
Cellulitis & Erysipelas - Classification
1) Presence of purulence
2) Anatomical site
Cellulitis:
1) Purulent OR Non-purulent
2) Epidermis, dermis, sometimes superficial fascia; May invade lymphatic tissue & blood
Erysipelas:
1) Non-purulent
2) Superficial dermis & lymphatic tissue
Cellulitis & Erysipelas - Clinical presentation
Cellulitis:
Poorly demarcated area of erythema
Purulent or non-purulent
Erysipelas:
Sharply demarcated area of erythema, with raised border
Non-purulent
Cellulitis & Erysipelas - Complications
1) Endocarditis
2) Bacteremia
3) Lymphedema
4) Glomerulonephritis
5) Osteomyelitis
6) Toxic shock
7) Necrotizing soft tissue infections (e.g. necrotizing fasciitis)
Cellulitis & Erysipelas - Microbiology
1) S. aureus
- Usually causes purulent infections
2) ß-hemolytic Streptococcus (e.g. S. pyogenes)
- Almost always cause of erysipelas
3) Others, depending on comorbidities & mode of injury
Cellulitis & Erysipelas - Additional causative organisms in patients with specific comorbidities
Immunosuppressed:
1) S. pneumoniae
2) E. coli
3) P. aeruginosa
4) Serratia marcescens
Chronic liver/renal disease
1) Vibrio spp.
2) P. aeruginosa
3) E. coli
Cellulitis & Erysipelas - Additional causative organisms, depending on mode of injury
Human bite
1) Pasteurella multocida
2) Oral anaerobes
Animal bite
1) Eikenella corrodens
2) Oral anaerobes
Cellulitis & Erysipelas - Culture
1) Need to culture
2) Types of cultures
1) Not routinely recommended
Consider culture if:
- Purulent infections after I&D
- Immunosuppressed (e.g. chemotherapy, transplant), SIRS criteria
2) Cutaneous aspirates
Tissue samples
Blood
Swabs
Cellulitis & Erysipelas - Severity definition
Mild:
- No SIRS criteria (no systemic infection)
Moderate:
- ≥ 1 SIRS criteria
Severe:
- > 2 SIRS criteria AND
- Hypotension (BP < 100/60 mmHg) OR Rapid progression OR Immunosuppression OR Comorbidities
Empiric therapy of NON-PURULENT, MILD cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus spp.
2) Oral
Antibiotics: Penicillin VK - PO 250-500 mg QDS - Preferred --> narrower spectrum (only covers Streptococcus) Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment needed in renal impairment Clindamycin - PO 300 mg QDS - Alternative in penicillin allergy
Empiric therapy of NON-PURULENT, MODERATE cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus +/- MSSA
2) PO if 1 SIRS criteria
IV if ≥ 2 SIRS criteria OR failed oral treatment
Oral antibiotics:
Penicillin VK - PO 250-500 mg QDS
Cloxacillin - PO 250-500 mg QDS
- Preferred –> covers both Streptococcus & MSSA
Cephalexin - PO 250-500 mg QDS
- Dose adjustment needed in renal impairment
- Preferred –> covers both Streptococcus & MSSA
Clindamycin - PO 300 mg QDS
- Alternative in penicillin allergy
IV antibiotics:
Penicillin G - IV 2-4 million units q4-6h
- Dose adjustment needed in renal impairment
Cefazolin - IV 1-2g q8h
- Dose adjustment needed in renal impairment
- Commonly used –> covers both Streptococcus & MSSA
Clindamycin - IV 600 mg q8h
- Alternative in penicillin allergy
Empiric therapy of NON-PURULENT, SEVERE cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus + S. aureus + GN (including P. aeruginosa)
2) IV
Antibiotics (No MRSA coverage)
Cefepime - IV 2g q8h
- Dose adjustment needed in renal impairment
Piperacillin-Tazobactam - IV 4.5g q6-8h
- Dose adjustment needed in renal impairment
Meropenem - IV 1g q8h
- Reserved for more resistant organisms
ADD ON for MRSA coverage:
Vancomycin - IV 15 mg/kg q8-12h
- Dose adjustment needed in renal impairment
- Preferred –> narrower spectrum, less costly
Daptomycin - IV 4-6 mg/kg once daily
- Dose adjustment needed in renal impairment
Linezolid - IV 600 mg q12h
Empiric therapy of PURULENT, MILD cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus + S. aureus
2) PO
Antibiotics (No MRSA coverage): Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment for renal impairment Clindamycin - PO 300 mg QDS - Alternative for penicillin allergy
Antibiotics (MRSA coverage): Clindamycin - PO 300 mg QDS Cotrimoxazole - PO 800/160 mg BD - Dose adjustment needed in renal impairment Doxycycline - PO 100 mg BD
Empiric therapy of PURULENT, MODERATE cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus + S. aureus
2) PO if 1 SIRS criteria
IV if ≥ 2 SIRS criteria OR Treatment failure with oral antibiotics
Oral antibiotics (no MRSA coverage): Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment needed in renal impairment Clindamycin - PO 300 mg QDS - Alternative for penicillin allergy
Oral antibiotics (MRSA coverage): Clindamycin - PO 300 mg QDS Cotrimoxazole - PO 800/160 mg BD - Dose adjustment needed in renal impairment Doxycycline - PO 100 mg BD
IV antibiotics (no MRSA coverage): Cloxacillin - IV 1-2g q4-6h Cefazolin - IV 1-2g q8h - Dose adjustment needed in renal impairment Clindamycin - IV 600 mg q8h
IV antibiotics (MRSA coverage):
Vancomycin - IV 15 mg/kg q8-12h
- Dose adjustment needed in renal impairment
Daptomycin - IV 4-6 mg/kg once daily
- Dose adjustment needed in renal impairment
Linezolid - IV 600 mg q12h
Empiric therapy of PURULENT, SEVERE cellulitis & erysipelas
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus + S. aureus + Gram-negative (including P. aeruginosa)
2) IV
Antibiotics (no MRSA coverage):
Piperacillin-Tazobactam - IV 4.5 q4-6h
- Dose adjustment needed in renal failure
Cefepime - IV 2g q8h
- Dose adjustment needed in renal failure
Meropenem - IV 1g q8h
- Dose adjustment needed in renal failure
ADD ON for MRSA coverage:
Vancomycin - IV 15 mg/kg q8-12h
- Dose adjustment needed in renal failure
Daptomycin - IV 4-6 mg/kg once daily
- Dose adjustment needed in renal failure
Linezolid - IV 600 mg q12h
Empiric therapy of cellulitis from bite wounds
1) Organisms to cover
2) Route
3) Antibiotics & dosing
1) Streptococcus + S. aureus + Gram-negatives + Anaerobes
2) PO or IV, depending on severity of infection
Antibiotics:
Amoxicillin-Clavulanate (Augmentin)
Ceftriaxone / Cefuroxime + Clindamycin / Metronidazole
Ciprofloxacin / Levofloxacin + Clindamycin / Metronidazole
Dosing:
Amoxicillin-Clavulanate - PO 625 mg BD-TDS / IV 1.2g q8h
- Dose adjustment needed for renal impairment
Clindamycin - PO 300 mg QDS / IV 600 mg q8h
Metronidazole - PO/IV 500 mg TDS
Empiric therapy of cellulitis & erysipelas - Duration
5 days (minimum) 7-14 days (immunosuppressed)
What is diabetic foot infection (DFI)
Skin tissue/Bone infection bellow the malleolus (occurs in diabetic patients)
DFI - Complications
1) Hospitalization
2) Osteomyelitis leading to amputation
DFI - Pathophysiology
1) Neuropathy
- Peripheral neuropathy: Decreased pain sensation & altered pain response
- Motor: Muscle imbalance –> increase risk of falls
- Autonomic: Increased dryness, cracks & fissures in skin –> point of entry for bacteria
2) Vasculopathy
- Due to early atherosclerosis, peripheral vascular disease
- Worsened by hyperglycemia & hyperlipidemia
3) Immunopathy
- Weakened immune response –> increase susceptibility to bacterial infection
- Worsened by hyperglycemia
Overall: Ulcer & wound formation –> bacterial colonization, penetration & proliferation –> DFI
DFI - Clinical presentation
Range of clinical presentation, with varying severity
E.g. Superficial ulcer, mild erythema
E.g. Deep tissue infection, extensive erythema
E.g. Infection of bone, fascia, purulent discharge
E.g. Localized gangrene
Pressure ulcers are also known as
Decubitus ulcers / Bed sores
Pressure ulcers are formed due to
Synergistic interaction between 4 factors:
1) Moisture
2) Pressure (duration & amount)
3) Shearing force
4) Friction
Pressure ulcers - Risk factors
1) Reduced mobility (e.g. spinal cord injury, paraplegic)
2) Debilitation due to severe chronic disease (e.g. multiple sclerosis, stroke, cancer)
3) Reduced consciousness
4) Sensory & autonomic impairment
5) Extremes of age
6) Malnutrition
DFI & Pressure ulcers - Microbiology
Typically polymicrobial
Most common:
1) S. aureus
2) Streptococcus
Others
1) Gram-negative
- E.g. E. coli, Klebsiella, Proteus
- P. aeruginosa less common
2) Anaerobes
- Peptostreptococcus, Veillonella, Bacteroides
DFI & Pressure ulcers - Cultures
Do NOT culture uninfected wounds
Cultures optional in mild DFIs
Types of cultures:
Deep tissue cultures (after cleansing & before starting antibiotics, if possible)
Biopsy specimens
Avoid skin swabs
DFI & Pressure ulcers - Criteria for infection
Purulent discharge OR ≥ 2 S/Sx of inflammation - Warmth - Erythema - Tenderness - Pain - Induration
DFI & Pressure ulcers - Severity definition
Based on severity classification by IDSA
Mild:
Infection of skin / SC tissue AND
Erythema ≤ 2 cm AND
No SIRS
Moderate:
Infection of deeper tissue (e.g. bone, joint) OR Erythema > 2 cm AND
No SIRS
Severe:
SIRS
Empiric therapy of DFI & Pressure ulcers - When to cover P. aeruginosa
Risk factors:
- Warm climate
- Frequent exposure to water
In SG:
- Severe infection
- Failure of antibiotics that do not cover P. aeruginosa
Empiric therapy of DFI & Pressure ulcers - Duration
No bone involved
Mild: 1-2 weeks
Moderate: 1-3 weeks
Severe: 2-4 weeks
Bone involved
Surgery, all infected bone & tissue removed (e.g. amputation): 2-5 days
Surgery, residual infected soft tissue: 1-3 weeks
Surgery, residual viable bone: 4-6 weeks
No surgery / Surgery, residual dead bone: ≥ 3 months
Empiric therapy of DFI & Pressure ulcers - Mild infection
1) Organisms to cover
2) Route
3) Antibiotics
1) Streptococcus + S. aureus
2) PO
Antibiotics (no MRSA coverage): Cloxacillin - PO 250-500 mg QDS Cephalexin - PO 250-500 mg QDS - Dose adjustment needed in renal impairment Clindamycin - PO 300 mg QDS - Alternative to penicillin allergy
Antibiotics (MRSA coverage): Clindamycin - PO 300 mg QDS Doxycycline - PO 100 mg BD Cotrimoxazole - PO 800/160 mg BD - Dose adjustment needed in renal impairment
Empiric therapy of DFI & Pressure ulcers - Moderate infection
1) Organisms to cover
2) Route
3) Antibiotics
1) Streptococcus + S. aureus + Gram-negative (+/- P. aeruginosa) + Anaerobes
2) IV
Antibiotics (without MRSA coverage):
Amoxicillin-Clavulanate - IV 1.2g q8h
- Dose adjustment needed in renal impairment
Ceftriaxone - IV 1-2g daily
- Dose adjustment needed in renal impairment
Ertapenem - IV 1g once daily
- Dose adjustment needed in renal impairment
ADD ON to Ceftriaxone for anaerobic coverage:
Clindamycin - IV 600 mg q8h
Metronidazole - IV 500 mg TDS
ADD ON for MRSA coverage: Vancomycin - IV 15 mg/kg q8-12h - Dose adjustment needed in renal impairment Daptomycin - IV 4-6 mg/kg once daily Linezolid - IV 600 mg q12h
Empiric therapy of DFI & Pressure ulcers - Severe infection
1) Organisms to cover
2) Route
3) Antibiotics
1) Streptococcus + S. aureus + Gram-negative (including P. aeruginosa) + Anaerobes
2) IV
Antibiotics (without MRSA coverage):
Piperacillin-Tazobactam - IV 4.5g q6-8h
- Dose adjustment needed in renal impairment
Cefepime - IV 2g q8h
- Dose adjustment needed in renal impairment
Meropenem - IV 1g q8h
- Dose adjustment needed in renal impairment
ADD ON to Cefepime for anaerobic coverage:
Clindamycin - IV 600 mg q8h
Metronidazole - IV 500 mg TDS
ADD ON for MRSA coverage: Vancomycin - IV 15 mg/kg q8-12h - Dose adjustment needed in renal impairment Daptomycin - IV 4-6 mg/kg once daily Linezolid - IV 600 mg q12h
Non-pharmacological management of DFI
1) Wound care
- Debridement
- “Off-loading” –> relieve pressure applied to wound area e.g. via wearing supportive shoes
- Dressings that promote healing environment & control excess exudation
2) Foot care
- Daily inspection
- Prevent wounds & ulcer formation
Non-pharmacological management of pressure ulcers
1) Debridement
2) Wound care
- Normal saline preferred
- Avoid harsh chemicals
3) Turn/Reposition every 2h
- Relieve pressure on wound
- Prevents pressure ulcers
