IC14 Skin & soft tissue Infections

Question 1

Classification: Anatomical sites

Answer 1

1. epidermis
2. dermis
3. hair follicle
4. SC fat
5. fascia
6. muscle

Question 2

epidermis infections

Answer 2

impetigo
* Superficial skin infection
* Presence of pustules/ vesicles that progress to crusting or bullae

Question 3

Dermis infections

Answer 3

ecthyma
* Deeper variant of impetigo
* Begins as vesicles/ pustules → evolves to ulcers

Erysipelas
* Superficial infection of skin; involves lymphatics
* Tender, erythematous plaque with well-demarcated borders

Cutaneous abscess
Localised collection of pus within dermis & deeper skin tissues

Question 4

hair follicle infections

Answer 4

Furuncles
* Infection of hair follicle
* Associated with small SC abscess

Folliculitis
Superficial infection of hair follicle + purulence in epidermis
Carbuncles
Cluster of furuncles

Question 5

SC tissue infection

Answer 5

Cellulitis
Acute infection involving deep dermis & subcutaneous fat

Question 6

fascia infections

Answer 6

Necrotising factors
Aggressive infection of SC tissue; spreads along fascial planes

Question 7

Muscles infection

Answer 7

Myositis

Pyomyositis
Purulent infection of skeletal muscle; often with abscess formation
Gas gangrene (clostridial myonecrosis)
Necrotising infection involving muscle

Question 8

3 main protective barrier of skin

Answer 8

physical
immunological
chemical

Question 9

derivation of SSTIs

Answer 9

disruption of normal host defences
Allows overgrowth & invasion of skin and soft tissues by pathogenic microorganisms

Question 10

risks factors

Answer 10

1. disruption of physical barrier of skin
2. conditions predisposed to infection

Question 11

RF: disruption of physical barrier of skin
traumatic

Answer 11

Lacerations, recent surgery, abrasions, crush injuries, open fractures, burns
Injection drug use
Human, animal & insect bites
Non-traumatic

Question 12

RF: disruption of physical barrier of skin
non-traumatic

Answer 12

Ulcers, tinea pedis, dermatitis, toe-web intertrigo
Chemical irritants

Question 13

RF: disruption of physical barrier of skin
impaired venous / lymphatic drainage

Answer 13

impaired BF
Saphenous venectomy, Obesity, Chronic venous insufficiency, peripheral artery disease

Impaired lymphatic drainage
Immune cells cannot reach site of infection quickly
Causes overgrowth of organism ⇒ invasion of tissues

Question 14

RF: conditions predisposed to infection

Answer 14

• suppression of immune system

DM, cirrhosis, neutropenia, HIV, transplantation & immunosuppressive medications
Hx of cellulitis

Question 15

clinical presentation
impetigo

progression, location, appearance

Answer 15

Begins as erythematous papules
Rapidly evolve into lesions → vesicles (clear fluid) & pustules (pus) ⇒ rupture
Dried discharge forms honey-coloured crusts on erythematous base

Usually on exposed areas of body: face & extremities

Lesions well localised, frequently many bullous/ non-bullous appearance

Question 16

clinical presentation furuncles

location of purulent material

Answer 16

Infection of hair follicle
Purulent material extends through dermis, into SC tissue ⇒ formation of abscess

Question 17

clinical presentation of carbuncles

location

Answer 17

Furuncle coalesce & extend into SC tissues

Question 18

clinical presentation
ecthyma

location, itch

Answer 18

Ulcerative form of impetigo
Lesions extend through epidermis & deep into dermis
Pruritus common; scratching may further spread infection

Question 19

clinical presentation of cutaneous abscess

location, symptoms

Answer 19

Collection of pus within dermis & deeper skin tissue
May be painful, tender, fluctuant & erythematous nodules

Question 20

clinical presentation of cellulitis

location, description of skin, onset, fever

Answer 20

Deeper & SC fats
Presents as acute, diffuse, spreading, non-elevated, poorly demarcated area of erythema
Relatively rapid onset/ progression
Mostly unilateral
Fever in 20-70% of patients
Normally on lower extremities

Question 21

clinical presentation of erysipielas

location, description of skin

Answer 21

Affect upper dermis
Fiery red, tender, painful plaque (raised above surrounding skin) with well demarcated edges
Common on face & lower extremities

Question 22

Culture to confirm infection

types, required individuals & how to obtain

Answer 22

Required for pus, exudates or tissues from wounds:
* Where sample should be collected
Deep in wound after cleaning surface
Base of closed abscess → where bacteria grow
By curettage → debriding top part, then remove tissue
* Problems (avoid taking sample from)
Open, draining wounds → often contaminated with potentially pathogenic organisms
Avoid wound swabs → difficult to obtain representative sample

Blood culture
For severe cases with marked systemic symptoms of infection
For immunocompromised patients

Question 23

complications of SSTIs

Answer 23

Bacteremia
* can stick to heart valves (endocarditis), spine (osteomyelitis)
* Release of toxins (toxic shock → common in immunocompromised patients)

Question 24

likely pathogen: impetigo

Answer 24

Staphylococci OR streptococci
Bullous form → toxin-producing strains of S.aureus

Question 25

likely pathogen: ecthyma

Answer 25

Group A streptococci

Question 26

likely pathogen: nonpurulent | Cellulitis, Erysipelas

Answer 26

B-hemolytic streptococcus (main) Group A streptococci (Strep. Pyogenes) **Less common pathogens** S.aureus, Aeromonas, Vibrio Vulnificus Pseudomonas with water exposure (or near to GI)

Question 27

likely pathogen: purulent | Furuncles, Carbuncles, Skin abscess, Purulent cellulitis

Answer 27

S.aureus (main) B-hemolytic streptococcus (some)

Question 28

community acquired MRSA | RF, possible treatment

Answer 28

**Possible treatments: PO non-beta lactam** Clindamycin, co-trimoxazole, doxycycline **Risk factors:** * participants of contact sports, military personnel, IV drug abusers (IVDA), prison inmates * overcrowded facilities, close contact & lack of sanitation ⇒ contributes to spread

Question 29

hospital acquired MRSA | requirements/ classifications, RF

Answer 29

**Requirements/ classifications** * >48 hours following hospitalisation * Outside hospital within 12 months exposure to healthcare **Risk factors:** * AB use, recent hospitalisation/ surgery, prolonged hospitalisation, intensive care * MRSA colonisation, close proximity to others with MRSA colonisation/ infection

Question 30

impetigo management (mild, limited lesions)

Answer 30

Topical Mupirocin BD x 5 days Effective against aerobic G+ (esp S.aureus)

Question 31

impetigo (multiple lesions) & ecthyma managment | duration of treatment, empiric & culture therapy

Answer 31

**Duration of treatment:** 7 days **Empiric** PO cephalexin or cloxacillin ⇒ can assume susceptible PO clindamycin → for penicillin allergy **Culture-directed (definitive)** S.pyogenes: PO penicillin V, amoxicillin MSSA: PO cephalexin or cloxacillin

Question 32

nonpurulent management: mild | classification & symptoms; therapy

Answer 32

**(w/o systemic signs of infection)** Mainly cover Strep pyogenes * PO penicillin V, cephalexin, cloxacillin If have bacteremia, use IV penicillin G No coverage for MSSA * PO clindamycin → for penicillin allergy

Question 33

nonpurulent management duration of treatment

Answer 33

5-10 days, 14 days for immunocompromised

Question 34

nonpurulent management: moderate | classification & symptoms; therapy

Answer 34

**(w systemic signs of infection; some purulence)** Cover Strep pyogenes & MSSA * IV cefazolin, cloxacillin * IV Clindamycin → for penicillin allergy

Question 35

nonpurulent management: severe | classification & symptoms; therapy

Answer 35

**(w systemic signs of infection, failed PO therapy/ immunocompromised)** Broader coverage: G+, G-, anaerobes + necrotising infections * IV piperacillin-tazobactam, cefepime, meropenem * MRSA RF → add IV vancomycin, daptomycin, linezolid

Question 36

nonpurulent management: Risk factors

Answer 36

Ensure rest & limb elevation Drainage of edema & inflammatory substances Treat underlying conditions

Question 37

purulent management: main therapy

Answer 37

Insertion & drainage

Question 38

purulent management: when to consider systemic AB

Answer 38

* Unable to drain completely; Lack of response to I&D * Extensive disease involving several sites; severe disease * Extremes of age * Immunosuppressed (ie: chemotherapy, transplant) * Signs of systemic illness * SIRS criteria: (any 2/4 met = systemic) Temperature > 38degC or < 36degC; HR > 90 bpm RR > 24 bpm WBC > 12 x 10^9/L or < 4 x 10^9/L

Question 39

purlent management: empiric | duration of treatment, MRSA, G-, Long hospitalisation, ICU

Answer 39

5-10 days **Empiric (MRSA): G+ & MRSA** Cotrimoxazole, doxycycline, clindamycin Vancomycin Daptomycin, linezolid → for vancomycin-resistant bacteria OR if have nephrotoxicity to vancomycin **Empiric (G-, anaerobe): G+ & G-** Usually near anal area, gut, rectal area Amoxicillin-clavulanate **Resistant risks & long hospital stay:** Piperacillin-tazobactam **ICU & septic shock**: Carbapenem (To cover for ESBLs)

Question 40

purulent management: culture directed | mild, moderate, severe

Answer 40

**Mild infection** I&D or warm compress to promote drainage **Moderate (with systemic symptoms)** I&D AND PO cloxacillin or cephalexin PO clindamycin → for penicillin allergy **Severe** I&D AND IV cloxacillin or cefazolin IV Clindamycin → for penicillin allergy IV Vancomycin ⇒ if have allergy + Covers MRSA

Question 41

DFI: background | areas of DFI, complications

Answer 41

Soft tissue/ bone infections below malleolus **Areas of DFI** Skin ulceration → peripheral neuropathy Wound → trauma **Complications** Hospitalisation Osteomyelitis ⇒ deep infection requiring amputation

Question 42

DFI: diagnosis | Criteria for infection

Answer 42

Bacterial colonisation of ulcers/ wounds **Criteria for infection** * Purulent discharge * ≥ 2 signs or symptoms of inflammation: Erythema, warmth, tenderness, pain, induration

Question 43

DFI: Pathophysiology & outcomes

Answer 43

(1) neuropathy (2) vasculopathy (3) immunopathy formation of ulcers & wounds bacteria colonisation, penetration & proliferation leads to DFI

Question 44

DFI: Pathophysiology neuropathy

Answer 44

Peripheral: reduced pain sensation & altered pain response Motor: muscle imbalance Autonomic: increased dryness, cracks & fissures

Question 45

DFI: Pathophysiology immunopathy

Answer 45

Impaired immune response Increased susceptibility to infections Worsened by hyperglycemia

Question 46

DFI: Pathophysiology vasculopathy

Answer 46

Early atherosclerosis Peripheral vascular disease Worsened by hyperglycemia & hyperlipidemia

Question 47

DFI clinical presentation

Answer 47

* Superficial ulcer, mild erythema * Deep tissue infection, extensive erythema * Infection of bone & fascia; purulent discharge * Localised gangrene

Question 48

DFI & pressure wounds causative organisms

Answer 48

**Common**: Staphylococcus aureus & Streptococcus **Gram negative bacilli**→ E.coli, Klebsiella, Proteus * In chronic wounds/ previously treated with AB * Less common for P.aeruginosa **Anaerobes** → Peptostreptococcus spp., Veillonella spp., Bacteroides spp. * In ischemic/ necrotic wounds (very deep)

Question 49

DFI culture requirements

Answer 49

Moderate-severe DFIs Deep tissue culture after cleansing & before starting AB * In order to opt for narrow spectrum

Question 50

treatment of DFI & pressure wounds classification

Answer 50

1. Infection of skin & SC tissue If erythema ≤ 2 cm around ulcer No signs of systemic infection 2. Infection of deeper tissue (ie bone, joints) OR If erythema > 2 cm around ulcer No signs of systemic infection 3. Infection of deeper tissue OR If erythema > 2 cm around ulcer Signs of systemic infection

Question 51

treatment of DFI & pressure wounds organisms to cover

Answer 51

1. Streptococcus spp & S. aureus 2. Streptococcus spp, S. aureus, Gram negs (± P.aeruginosa), Anaerobes 3. Streptococcus spp, S. aureus, Gram negs (P.aeruginosa), Anaerobes

Question 52

treatment of DFI & pressure wounds therapy (No MRSA concern) | mild, mod, severe

Answer 52

1. PO Cephalexin Cloxacillin Clindamycin (Penicillin resistance) 2. Initial IV Amox/ clav Cefazolin/ ceftriaxone + metronidazole 3. Initial IV Pip-tazo Cefepime + metronidazole Meropenem Ciprofloxacin + clindamycin

Question 53

treatment of DFI & pressure wounds therapy (MRSA concern) | mild vs mod & severe

Answer 53

**Mild** (PO) Co-trimoxaxzole Clindamycin Doxycycline **moderate & severe** (IV) Vancomycin Daptomycin Linezolid

Question 54

treatment of DFI & pressure wounds duration of therapy | bone involved (surgery Vs no surgery)

Answer 54

**Surgery** Amputation (removal of all infected bone & tissues) ⇒ 2-5 days Residual infected soft tissue ⇒ 1-3 weeks Residual viable bone ⇒ 4-6 weeks **no surgery** Residual dead bone ⇒ ≥ 3 months

Question 55

treatment of DFI & pressure wounds duration of treatment | normal

Answer 55

1. 1-2 weeks 2. 1-3 weeks 3. 2-4 weeks

Question 56

treatment of DFI adjunctive therapy

Answer 56

**Wound care** Debridement Off loading → avoid weight on infected foot Apply dressings that promote healing environment & control excess exudation **Foot care** Daily inspection Prevent wounds & ulcers **Optimal glycemic control**

Question 57

factors causing pressure wound | SPFM

Answer 57

Moisture, pressure (amount & duration), shearing force, friction

Question 58

Adjunctive measures for pressure ulcers

Answer 58

**Debridement of infected/ necrotic tissue** **Local wound care** Use of normal saline Avoid harsh chemicals **Relief of pressure** turn/ reposition every 2 hours Use air/ water bed

Question 59

clinical presentation of pressure wounds (4 stages)

Answer 59

1. Abrasion of epidermis Irregular area of tissue swelling No open wound 2. Extension through dermis Open wound 3. Extend deep into SC fat Open sore/ ulcer 4. Involves muscle & bone Deep sore/ ulcer

Question 60

risk factors of pressure wounds | MMACCS

Answer 60

Reduced **mobility** (ie: spinal cord injuries, paraplegic) * Reduced **blood circulation** at area of pressure ⇒ breakage of skin Severe **chronic diseases** (ie: multiple sclerosis, stroke, cancer) Reduced **consciousness** **Sensory** & autonomic impairment → incontinence Extremes of **age** **Malnutrition**