SSTI

Question 1

Boundary Membrane Concept

Answer 1

• Exists on external aspects of body
• Consists of layer(s) epithelial cells bound to each other by tight junctions, overlies a basement membrane
• Provides water tight barrier
• Separates epithelium from underlying connective tissue space
• Microbial organisms live on the barrier membrane
• Kept outside of the interstitium by the barrier membrane
• No immune response is provoked

Question 2

Barrier Violation

Answer 2

• Injury to the boundary membrane allows microbial penetration into interstitium
• Bacterial virulence can be variable, from severe to minimal
• Contamination or infection

Question 3

Uncomplicated SSTIs

Answer 3

• Superficial: cellulitis, impetiginous lesions, furnucles, simple abscesses
• Treatment usually requires antibiotics and/or simple incision and drainage

Question 4

Complicated SSTI

Answer 4

• Deep soft tissue infections: extreme pain, violaceous bullae, cutaneous hemorrhage, skin sloughing, rapid progression, gas in tissue
• May require surgical intervention: infected ulcers, infected burns, and major abscesses
• Significant underlying disease which complicates the response to treatment
• May require extensive surgical debridement and reconstruction

Question 5

Microbiology of SSTIs

Answer 5

• S. aureus ~50%
• Strept. pyogenes
• Site specific infections: indigenous organisms
• Immunocompromised + Complicated SSTIs: multiple/uncommon organisms
• Polymicrobial necrotizing fasciitis: mixed infections with anaerobes and aerobes
• Monomicrobial necrotizing fasciitis: S. pyogenes

Question 6

Abscesses + Antibiotics Indications

Answer 6

• Antibiotics not necessary for most: usually just drain and wound care
• Signs of infection: fever, elevated WBCs, left shift, septic shock
• Cellulitis or phlegmon
• Immunocompromised
• Certain foreign bodies (Marlex mesh)

Question 7

Cellulitis

Answer 7

• Spreading infection affecting epidermis and dermis

- Common pathogen: GAS, S. aureus, Group B/C/G strept

Question 8

Cellulitis Presentation

Answer 8

• Swelling
• Redness
• Edema
• Pain
• Nonelevated
• Poorly defined margins
• Lymphadenopathy
• Fever/chills: rare unless chronic, underlying disease, or immunocompromised

Question 9

SSTI General Treatment Rules

Answer 9

-Antibiotic therapy: 10-14 days

Question 10

Purulent SSTI Treatment

Answer 10

• Mild Infection: purulent SSTI, incision and drainage indicated
• Moderate: patients with purulent infection with systemic signs of infection
• Severe: failed incision/drainage plus oral antibiotics or those with severe systemic signs, immunocompromised

Question 11

Severe Systemic Signs

Answer 11

• > 38 C Fever
• Tachycardia
• Tachypnea
• Abnormal WBC

Question 12

Nonpurulent SSTI Treatment

Answer 12

• Mild Infection: typical cellulitis/erysipelas with no focus of purulence
• Moderate: typical cellulitis/erysipelas with systemic signs of infection
• Severe: failed oral antibiotic/systemic signs of infection, immunocompromised, signs of deeper infection like bullae, sloughing, hypotension, or evidence of organ dysfunction

Question 13

Erysipelas

Answer 13

• Distinct type of superficial cellulitis with extensive lymphatic involvement
• Almost always GAS
• Common in infants, young kids, elderly, and patients with nephrotic syndrome
• Manifestation: lesion with sharp, elevated border, on face/scalp/hands/genitalia, fever and leukocytosis
• Treatment: Mild/moderate non-purulent SSTI

Question 14

Impetigo

Answer 14

• Superficial cellulitis by GAS (honey crust, non-bullous) and/or S. aureus (bullous, ruptured)
• Common in children during hot/humid weather
• Spread through close contact and little to no signs of systemic infection
• Small, fluid-filled vesicles that develop into puss-filled blisters that rupture and crust, pruritus

Question 15

Impetigo Treatment

Answer 15

• Depends on number of lesions, location, and need to limit spread
• Topical: mupirocin ointment to lesions TID
• Oral: numerous lesions, location prevents topical use, or not responding to topicals
• See moderate treatment for purulent SSTI

Question 16

Necrotizing Fasciitis

Answer 16

• SC infection that tracks along fascial planes and extends beyond superficial infection signs
• Extension from a lesion in 80% of cases
• Presentation: cellulitis which can advance rapidly with systemic toxicity (high fevers, lethargy, confusion), cellulitis, edema, skin discoloration or gangrene
• Usually lower extremities

Question 17

Necrotizing Fasciitis Etiology

Answer 17

• Monomicrobial: GAS, S. aureus, Clostridium spp. (mortality in 50-70% in pts. with hypotension/organ failure
• Polymicrobial: average of 5 per wound usually from surgical wounds, ulcers, or abscess

Question 18

Necrotizing Fasciitis Diagnosis

Answer 18

• Clinical judgement
• Incision and probing if no resistant to SC probing then Nec. Fasciitis
• Gram-stain and culture

Question 19

Necrotizing Fasciitis Treatment

Answer 19

-Prompt surgical debridement

Antibiotic Options

• PCN G 24 mU/day IV + Clinda 900 IV q8h (eagle effect)
• MRSA suspected: Add vanco (trough 15-20 mcg/mL)
• Polymicrobial: Vanco + Zosyn 3.375-4.5g IV q6-8h OR Imipenem 500 mg IV q6h OR Meropenem 1g IV q8h

Question 20

DFI

Answer 20

• Diabetic Foot Infections
• 15-20% of diabetics will get hospitalized for this
• Requires attention to local and systemic aspects
• Aerobic, Gram “+” are most common (S. aureus)
• Can get Gram “-“ with chronic infections and may be anaerobes if ischemia/gangrene arises
• Optimal DFI management can reduce infection related morbidity and the need/duration of hospitalization

Question 21

DFI Risk Factors

Answer 21

• Neuropathy
• Angiopathy and ischemia
• Immunologic defects

Question 22

DFI Presentation

Answer 22

• Polymicrobial in nature
• Often more extensive than they appear with paronychia, middle foot, toe web, mal perforans puncture wounds
• May be complicated by necrotizing cellulitis, osteomyelitis

Question 23

DFI Treatments

Answer 23

• Local wound care
• Immobilization
• Drainage and debridement
• Control of hyperglycemia
• Antibiotics: ORal v.s. IV for 2 weeks (6 for osteomyelitis)
• Amputation is LAST resort

Question 24

DFI Grades

Answer 24

• Grade 1-2: non-limb threatening
• Grade 3: Possibly limb threatening
• Grade 4: Limb threatening

Question 25

DFI Treatment Administration/Duration

Answer 25

- Mild: topical or oral, outpatient, 1-2 weeks and can extend to 4 weeks if slow to resolve - Moderate: Oral, outpatient or inpatient, 1-3 weeks - Severe: initiallyIV then switch to oral when possible, inpatient then outpatient, 2-4 weeks of treatment

Question 26

Dog Bites

Answer 26

- Localized cellulitis and pain - 5% become infected - Treat only if severe or co-morbidity - Likely pathogens: Pasteurella canis, S. aureus, Bacteroides spp.

Question 27

Dog Bite Treatment

Answer 27

- Augmentin 875/125 mg BID or 500/125 TID po - PCN Allergy: Clinda 450 mg TID OR Clinda + Bacrim in children * *Other options for adults not listed** - Duration: 10-14days - Consider rabies?

Question 28

Cat Bites

Answer 28

- Localized cellulitis and pain (osteo) - 80% become infected - Culture and treat empirically - Most like Pasteurella multocida or S. aureus

Question 29

Cat Bite Treatments

Answer 29

- Augmentin: 875/125 mg BID or 500/125 mg TID PO - Cefuroxime axetil: 500 mg BID PO (NO CEPHALEXIN) - Doxycycline 100 mg BID PO - Duration 10-14 days

Question 30

Human Bites

Answer 30

- Localized cellulitis and pain, purulent discharge, decreased range of motion (osteo, septic arthritis, tenosynovitis - More serious than animal bites with higher rates of infection - Likely pathogens: Viridans strept, S. epidermidis, corynebacterium, S. aureus, eikenella, Bacteroides spp., peptostreptococcus

Question 31

Human Bite Wound Treatment

Answer 31

- General: cleaning, irrigation, debridement | - Early (not infected): Augmentin 875/125 mg BID PO x 5 days

Question 32

Human Bites: Late Treatment

Answer 32

-Signs of infection, usually within 12-24 hours -Unasyn: 1.5-3g IV q6h OR -Cefoxitin 1g IV q8h OR -Zosyn 3.375 IV q6h or 4hr infusion 3.375g IV q8h -PCN allergy: Clinda 600-900mg IV q8h + Cipro 400 mg IV q12h OR Bactrim 10 mg/kg/day