SSTI

Question 1

Protecting factors of skin

Answer 1

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

Question 2

Pathophysiology of SSTIs

Answer 2

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

Question 3

Risk factors for SSTIs

Answer 3

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)

Question 4

Classification of SSTIs

Answer 4

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

Question 5

Types of SSTIs, based on anatomical site

Answer 5

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

Question 6

Common causative organisms of SSTIs

Answer 6

Most common:

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

Question 7

Community-acquired MRSA

1) Prevalence in SG
2) Risk factors

Answer 7

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

Question 8

SIRS criteria

Answer 8

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

Question 9

Impetigo & Ecthyma - Classification

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

Answer 9

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

Question 10

Impetigo & Ecthyma - Clinical presentation

Answer 10

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

Question 11

Impetigo & Ecthyma - Microbiology

Answer 11

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

Question 12

Impetigo & Ecthyma - Culture

Answer 12

Usually treated without culture

May culture if pus

Question 13

Empiric therapy of impetigo (most cases)

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

Answer 13

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

Antibiotics:
Mupirocin - Apply to affected area BID

Question 14

Empiric therapy of impetigo (severe cases)

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

Answer 14

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

Question 15

Empiric therapy of ecthyma

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

Answer 15

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

Question 16

Culture directed therapy for ecthyma (and severe impetigo)

Answer 16

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

Question 17

Purulent SSTIs - Types

Answer 17

1) Furuncles
2) Carbuncles
3) Cutaneous abscesses

Question 18

Purulent SSTIs - Classification

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

Answer 18

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

Question 19

Purulent SSTIs - Clinical presentation

Answer 19

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

Question 20

Purulent SSTIs - Risk factors

Answer 20

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

Question 21

Purulent SSTIs - Microbiology

Answer 21

S. aureus

Question 22

Purulent SSTIs - Culture

Answer 22

Usually treated without culture

Also reasonable to culture pus

Question 23

Management of purulent SSTIs

Answer 23

Mainstay treatmetn: Incision & drainage (I&D)

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

Question 24

When are adjunctive systematic antibiotics recommended in purulent SSTIs

Answer 24

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

Question 25

Empiric therapy of purulent SSTIs - Organisms to cover

Answer 25

MSSA | Only cover MRSA if patient has any MRSA risk factor

Question 26

Empiric therapy of purulent SSTIs - Route

Answer 26

Oral usually adequate | IV only needed for more severely ill patients (require hospital admission)

Question 27

Empiric therapy of purulent SSTIs - Duration

Answer 27

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

Question 28

Empiric therapy of purulent SSTIs - Antibiotics & dosing

Answer 28

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 ```

Question 29

Cellulitis & Erysipelas - Classification 1) Presence of purulence 2) Anatomical site

Answer 29

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

Question 30

Cellulitis & Erysipelas - Clinical presentation

Answer 30

Cellulitis: Poorly demarcated area of erythema Purulent or non-purulent Erysipelas: Sharply demarcated area of erythema, with raised border Non-purulent

Question 31

Cellulitis & Erysipelas - Complications

Answer 31

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

Question 32

Cellulitis & Erysipelas - Microbiology

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

Human bite 1) Pasteurella multocida 2) Oral anaerobes Animal bite 1) Eikenella corrodens 2) Oral anaerobes

Question 35

Cellulitis & Erysipelas - Culture 1) Need to culture 2) Types of cultures

Answer 35

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

Question 36

Cellulitis & Erysipelas - Severity definition

Answer 36

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

Question 37

Empiric therapy of NON-PURULENT, MILD cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 37

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 ```

Question 38

Empiric therapy of NON-PURULENT, MODERATE cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 38

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

Question 39

Empiric therapy of NON-PURULENT, SEVERE cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 39

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

Question 40

Empiric therapy of PURULENT, MILD cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 40

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 ```

Question 41

Empiric therapy of PURULENT, MODERATE cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 41

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

Question 42

Empiric therapy of PURULENT, SEVERE cellulitis & erysipelas 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 42

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

Question 43

Empiric therapy of cellulitis from bite wounds 1) Organisms to cover 2) Route 3) Antibiotics & dosing

Answer 43

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

Question 44

Empiric therapy of cellulitis & erysipelas - Duration

Answer 44

``` 5 days (minimum) 7-14 days (immunosuppressed) ```

Question 45

What is diabetic foot infection (DFI)

Answer 45

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

Question 46

DFI - Complications

Answer 46

1) Hospitalization | 2) Osteomyelitis leading to amputation

Question 47

DFI - Pathophysiology

Answer 47

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

Question 48

DFI - Clinical presentation

Answer 48

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

Question 49

Pressure ulcers are also known as

Answer 49

Decubitus ulcers / Bed sores

Question 50

Pressure ulcers are formed due to

Answer 50

Synergistic interaction between 4 factors: 1) Moisture 2) Pressure (duration & amount) 3) Shearing force 4) Friction

Question 51

Pressure ulcers - Risk factors

Answer 51

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

Question 52

DFI & Pressure ulcers - Microbiology

Answer 52

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

Question 53

DFI & Pressure ulcers - Cultures

Answer 53

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

Question 54

DFI & Pressure ulcers - Criteria for infection

Answer 54

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

Question 55

DFI & Pressure ulcers - Severity definition

Answer 55

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

Question 56

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

Answer 56

Risk factors: - Warm climate - Frequent exposure to water In SG: - Severe infection - Failure of antibiotics that do not cover P. aeruginosa

Question 57

Empiric therapy of DFI & Pressure ulcers - Duration

Answer 57

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

Question 58

Empiric therapy of DFI & Pressure ulcers - Mild infection 1) Organisms to cover 2) Route 3) Antibiotics

Answer 58

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 ```

Question 59

Empiric therapy of DFI & Pressure ulcers - Moderate infection 1) Organisms to cover 2) Route 3) Antibiotics

Answer 59

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 ```

Question 60

Empiric therapy of DFI & Pressure ulcers - Severe infection 1) Organisms to cover 2) Route 3) Antibiotics

Answer 60

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 ```

Question 61

Non-pharmacological management of DFI

Answer 61

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

Question 62

Non-pharmacological management of pressure ulcers

Answer 62

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