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SSTI Flashcards

1
Q

Protecting factors of skin

A

1) Dry surface
2) Fatty acids –> skin surface is acidic (pH ~5.6)
3) Renewal of epidermis
4) Low temperature (VS core body temperature)

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2
Q

Pathophysiology of SSTIs

A

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

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3
Q

Risk factors for SSTIs

A

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)

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4
Q

Classification of SSTIs

A

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

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5
Q

Types of SSTIs, based on anatomical site

A

1) Epidermis - Impetigo
2) Dermis - Ecthyma; Erysipelas
3) Hair follicles - Furuncles, Carbuncles
4) Subcutaneous fat - Cellulitis
5) Fascia - Necrotizing fasciitis
6) Muscle - Myositis

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6
Q

Common causative organisms of SSTIs

A

Most common:

1) Staphylococcus aureus (MSSA)
2) ß-hemolytic Streptococci (e.g. S. pyogenes)

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7
Q

Community-acquired MRSA

1) Prevalence in SG
2) Risk factors

A 
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

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8
Q

SIRS criteria

A

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

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9
Q

Impetigo & Ecthyma - Classification

1) Severity
2) Depth of infection
3) Presence of discharge
4) Microbiology
5) Anatomical site

A

1) Usually mild
2) Superficial (uncomplicated)
3) Purulent or non-purulent
4) Single organsim
5) Impetigo - Epidermis; Ecthyma - Up to dermal-epidermal junction

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10
Q

Impetigo & Ecthyma - Clinical presentation

A

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

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11
Q

Impetigo & Ecthyma - Microbiology

A

1) S. aureus
- Usually causes bullous form
2) ß-hemolytic Streptococci (e.g. S. pyogenes)

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12
Q

Impetigo & Ecthyma - Culture

A

Usually treated without culture

May culture if pus

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13
Q

Empiric therapy of impetigo (most cases)

1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing

A

1) MSSA, ß-hemolytic Streptococcus
2) Topical
3) 5 days

Antibiotics:
Mupirocin - Apply to affected area BID

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14
Q

Empiric therapy of impetigo (severe cases)

1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing

A

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
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15
Q

Empiric therapy of ecthyma

1) Organisms to cover
2) Route
3) Duration
4) Antibiotics & dosing

A

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
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16
Q

Culture directed therapy for ecthyma (and severe impetigo)

A

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

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17
Q

Purulent SSTIs - Types

A

1) Furuncles
2) Carbuncles
3) Cutaneous abscesses

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18
Q

Purulent SSTIs - Classification

1) Presence of purulence
2) Microbiology
3) Anatomical site

A

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

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19
Q

Purulent SSTIs - Clinical presentation

A

Furuncles - Inflammatory nodule
Carbuncles - Forms small abscess; Larger & deeper than furuncles
Cutaneous abscess - Nodule with a rim of erythematous swelling; Pus collection

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20
Q

Purulent SSTIs - Risk factors

A

1) Close physical contact
2) Crowded living conditions
3) Sharing of personal items
4) Poor personal hygiene

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21
Q

Purulent SSTIs - Microbiology

A

S. aureus

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22
Q

Purulent SSTIs - Culture

A

Usually treated without culture

Also reasonable to culture pus

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23
Q

Management of purulent SSTIs

A

Mainstay treatmetn: Incision & drainage (I&D)

Systemic antibiotics only recommended in certain select situations (adjunctive therapy)

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24
Q

When are adjunctive systematic antibiotics recommended in purulent SSTIs

A

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

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25
Q

Empiric therapy of purulent SSTIs - Organisms to cover

A

MSSA

Only cover MRSA if patient has any MRSA risk factor

26
Q

Empiric therapy of purulent SSTIs - Route

A

Oral usually adequate

IV only needed for more severely ill patients (require hospital admission)

27
Q

Empiric therapy of purulent SSTIs - Duration

A

Outpatient: 5-7 days
Inpatient: 7-14 days

28
Q

Empiric therapy of purulent SSTIs - Antibiotics & dosing

A

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
29
Q

Cellulitis & Erysipelas - Classification

1) Presence of purulence
2) Anatomical site

A

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

30
Q

Cellulitis & Erysipelas - Clinical presentation

A

Cellulitis:
Poorly demarcated area of erythema
Purulent or non-purulent

Erysipelas:
Sharply demarcated area of erythema, with raised border
Non-purulent

31
Q

Cellulitis & Erysipelas - Complications

A

1) Endocarditis
2) Bacteremia
3) Lymphedema
4) Glomerulonephritis
5) Osteomyelitis
6) Toxic shock
7) Necrotizing soft tissue infections (e.g. necrotizing fasciitis)

32
Q

Cellulitis & Erysipelas - Microbiology

A

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

33
Q

Cellulitis & Erysipelas - Additional causative organisms in patients with specific comorbidities

A

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

34
Q

Cellulitis & Erysipelas - Additional causative organisms, depending on mode of injury

A

Human bite

1) Pasteurella multocida
2) Oral anaerobes

Animal bite

1) Eikenella corrodens
2) Oral anaerobes

35
Q

Cellulitis & Erysipelas - Culture

1) Need to culture
2) Types of cultures

A

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

36
Q

Cellulitis & Erysipelas - Severity definition

A

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
37
Q

Empiric therapy of NON-PURULENT, MILD cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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
38
Q

Empiric therapy of NON-PURULENT, MODERATE cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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

39
Q

Empiric therapy of NON-PURULENT, SEVERE cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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

40
Q

Empiric therapy of PURULENT, MILD cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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
41
Q

Empiric therapy of PURULENT, MODERATE cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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

42
Q

Empiric therapy of PURULENT, SEVERE cellulitis & erysipelas

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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

43
Q

Empiric therapy of cellulitis from bite wounds

1) Organisms to cover
2) Route
3) Antibiotics & dosing

A

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

44
Q

Empiric therapy of cellulitis & erysipelas - Duration

A 
5 days (minimum)
7-14 days (immunosuppressed)
45
Q

What is diabetic foot infection (DFI)

A

Skin tissue/Bone infection bellow the malleolus (occurs in diabetic patients)

46
Q

DFI - Complications

A

1) Hospitalization

2) Osteomyelitis leading to amputation

47
Q

DFI - Pathophysiology

A

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

48
Q

DFI - Clinical presentation

A

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

49
Q

Pressure ulcers are also known as

A

Decubitus ulcers / Bed sores

50
Q

Pressure ulcers are formed due to

A

Synergistic interaction between 4 factors:

1) Moisture
2) Pressure (duration & amount)
3) Shearing force
4) Friction

51
Q

Pressure ulcers - Risk factors

A

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

52
Q

DFI & Pressure ulcers - Microbiology

A

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

53
Q

DFI & Pressure ulcers - Cultures

A

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

54
Q

DFI & Pressure ulcers - Criteria for infection

A 
Purulent discharge OR
≥ 2 S/Sx of inflammation
- Warmth
- Erythema
- Tenderness
- Pain
- Induration
55
Q

DFI & Pressure ulcers - Severity definition

A

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

56
Q

Empiric therapy of DFI & Pressure ulcers - When to cover P. aeruginosa

A

Risk factors:

  • Warm climate
  • Frequent exposure to water

In SG:

  • Severe infection
  • Failure of antibiotics that do not cover P. aeruginosa
57
Q

Empiric therapy of DFI & Pressure ulcers - Duration

A

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

58
Q

Empiric therapy of DFI & Pressure ulcers - Mild infection

1) Organisms to cover
2) Route
3) Antibiotics

A

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
59
Q

Empiric therapy of DFI & Pressure ulcers - Moderate infection

1) Organisms to cover
2) Route
3) Antibiotics

A

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
60
Q

Empiric therapy of DFI & Pressure ulcers - Severe infection

1) Organisms to cover
2) Route
3) Antibiotics

A

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
61
Q

Non-pharmacological management of DFI

A

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

62
Q

Non-pharmacological management of pressure ulcers

A

1) Debridement
2) Wound care
- Normal saline preferred
- Avoid harsh chemicals
3) Turn/Reposition every 2h
- Relieve pressure on wound
- Prevents pressure ulcers

ID (12 decks)

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