Skin & Soft Tissue Infections Flashcards
How does the skin serve as a protective barrier to infection?
- Physical barrier
- barrier from physical, microbial, chemical assaults
- prevent excessive water loss
- Chemical barrier
- acidic pH 4-5 (FFAs from phospholipids)
- acidic environment keep bacteria and candida low, regulate desquamation
- continuous renewal of epidermal layer, results in shedding of keratocytes and skin microbiota
- sebaceous secretions inhibit growth of many bacteria and fungi
- normal commensal skin microbiome prevents overgrowth and colonization of pathogenic strains
- Immunological barrier
- innate (physical barrier + AMPs antimicrobial peptides, cytokines, cells with PRR)
- AMP kills pathogens, influences cellular processes to promote wound healing, initiation of adaptive immune response, controls inflammation
What factors impair skin barrier function?
Age
Infection
Physical damage
Physical environment
Ischemia - lack of perfusion
Diseases (e.g., DM)
Drugs
pH
Excessive soap and detergent use
Too much moisture and humidity
What are the classification of SSTIs that occur at each anatomical site?
(Epidermis, Dermis, Hair follicles, Subcutaneous fat, Fascia, Muscle)
Epidermis - Impetigo
Dermis - Ecthyma, Erysipelas
Hair follicles - Furuncle, Carbuncle
Subcutaneous fat - Cellulitis
Fascia - Necrotizing fasciitis
Muscle - Myositis
What are some other protective mechanisms of the skin?
- Continuous renewal of epidermal layer, results in shedding of keratocytes and skin microbiota
- Sebaceous secretions inhibit growth of many bacteria and fungi
- Normal commensal skin microbiome prevents overgrowth and colonization of pathogenic strains
What are some risk factors for SSTI?
Disruption of the skin barrier
- Traumatic: lacerations, recent surgery, burns, abrasions…
- Non traumatic: pressure ulcers, tinea pedis, dermatitis, toe web intertrigo, chemical irritants
- impaired venous and lymphatic drainage: obesity, saphenous venectomy
- peripheral artery disease
Conditions / underlying diseases that predispose to infection
- DM, cirrhosis, neutropenia, HIV, transplant, immunosuppression
History of cellulitis
Also look out for: animal exposure, water exposure, travel history
How can SSTI be prevented?
Management of predisposing risk factors => identify at time of initial diagnosis to decrease risk for recurrence
Good care to maintain skin integrity
- good wound care
- treatment of tinea pedis
- preventing dry, cracked skin
- good foot care for DM patients to prevent wound and ulcers
Acute traumatic wound should be irrigated, foreign objects removed, devitalized tissues debrided
- Confirm presence of infection
When is culture required?
Bacteria culture is NOT required for mild and superficial infections (no systemic symptoms)
Blood culture is only required for severe cases with marked systemic symptoms of infection or immunocompromised patients
- E.g., lab (TW, CRP, creatinine phosphokinase, lactate, gram stain and culture)
- If sinister pathology suspected: radiography, CT with contrast, MRI, ultrasonography
- Confirm presence of infection
How should cultures of pus, exudates or tissues from wounds be taken?
Avoid wound swabs - colonizers, contaminants => polymicrobial
Cultures should be collected:
- from deep in the wound after surface cleansed
- from base of a closed abscess, where bacteria grow
- by curettage, rather than wound swab or irrigation
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of Impetigo
Epidermis, superficial infection
Begin as erythematous papules, evolve into vesicles and pustules that rupture with dried discharge forming honey-coloured crusts on an erythematous base
Usually on exposed areas of the body (face, extremities)
Lesions well localized, frequently many, bullous, or non-bullous
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of Ecthyma
Dermis, deeper variant of impetigo that extend through the epidermis and deep into dermis
Begin as vesicles/pustules, evolve into “punched out” ulcers (ulcerative form of impetigo)
Pruritis is common
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of Furuncle and Carbuncle
Furuncle: Infection of the hair follicle with purulent material, extends through the dermis into s/c tissue, small abscess forms
Carbuncle: furuncles coalesce, extent into s/c tissues
*PURULENT
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of cutaneous abscess
Skin abscess: localized collection of pus within the dermis and deeper skin tissues
Manifest as painful, tender, fluctuant, and erythematous nodules
*PURULENT
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of Erysipelas
Dermis
Affects upper dermis, more superficial, involves lymphatics
Fiery red, tender, painful plaque (raised) with well-demarcated edges
Common on face, lower extremities
*NON-PURULENT
- Confirm presence of infection (diagnosis - clinical presentation)
Describe the clinical presentation of Cellulitis
S/C tissue, involve deeper and subcutaneous fats
Usually acute, diffuse, spreading, non-elevated, poorly demarcated edges
Rapid onset/progression
Unilateral
Fever in 20-70% of patients
Common in lower extremities, though may appear on any area of the skin
*PURULENT or NON-PURULENT
- Confirm presence of infection (diagnosis - clinical presentation)
What are some cellulitis mimickers?
Deep venous thrombosis
Calciphylaxis
Stasis dermatitis
Hematoma
Erythema migrans
*if cant differentiate, may give a short course to monitor for response
- Confirm presence of infection (diagnosis - clinical presentation)
What are some complications that can arise if cellulitis progresses?
Bacteremia
Endocarditis
Toxic shock (overgrowth of staphs/streps => release toxins)
Glomerulonephritis
Lymphedema
Osteomyelitis
Necrotizing soft-tissue infections (Necrotizing fascia)
- Identify pathogens
Name the likely pathogens for Impetigo
Impetigo
- Staphylococci or Streptococci
- Bullous form caused by toxin-producing strains of S. aureus
- Identify pathogens
Name the likely pathogens for Ecthyma
Ecthyma
- Group A Streptococci
- Identify pathogens
Name the likely pathogens for Nonpurulent (Erysipelas, Cellulitis)
Nonpurulent
- Beta-hemolytic streptococcus, usually GAS (Strep. Pyogenes)
- S. aureus less frequent
- Others based on exposure: aeromonas (fresh water), vibrio vulnificus (sea water), pseudomonas (water exposure, hot tub)
- Identify pathogens
Name the likely pathogens for Purulent (Furuncle, Carbuncle, Skin abscesses, Cellulitis)
Purulent
- S. aureus
- Some beta-hemolytic strep
- Gram-negative and anaerobes may be common in pt with skin abscess involving perioral, perirectal, vulvovaginal area
- Identify pathogens
What is the difference between CA-MRSA and HA-MRSA?
What is used to treat CA-MRSA?
Why is CA-MRSA not a concern in Singapore?
CA-MRSA and HA-MRSA are genetically distinct
CA-MRSA
- Panton-Valentine Leucocidin (PVL) - enzyme breaks down WBC, infection has more abscess and pus
- SCCmec IV
CA-MRSA treatment
- Oral non-beta lactams (e.g., clindamycin, co-trimoxazole, doxycyline), IV vancomycin
CA-MRSA has low incidence in Singapore
Risk factors include:
- international schools
- participants of contact sports, military personnel, IV drug abusers, prison inmates
- overcrowded facilities, close contact, lack of sanitation
- Selection of antimicrobial and regimen
Impetigo and Ecthyma
Discuss the antibiotic selection for Impetigo with mild limited lesions
Impetigo - Staph or Strep
Ecthyma - GAS
Impetigo (mild limited lesions):
- Topical Mupirocin BID x5d
- Selection of antimicrobial and regimen
Impetigo and Ecthyma
Discuss the EMPIRIC antibiotic selection for Impetigo and Ecthyma
Impetigo - Staph or Strep
Ecthyma - GAS
Empiric - Cover staph + strep
- PO Cephalexin 500mg q6h
- PO Cloxacillin 500mg-1g q6h
- PO Clindamycin 300-450mg q6h (if allergic to penicillin) - SE: CDAD
*Treatment duration for oral: 7 days
- Selection of antimicrobial and regimen
Impetigo and Ecthyma
Discuss the CULTURE-DIRECTED antibiotic selection for Impetigo and Ecthyma (if Strep Pyogenes)
Impetigo - Staph or Strep
Ecthyma - GAS
Culture directed (GAS):
- PO Penicillin V 500mg q6h
- PO Amoxicillin 500mg-1g q8h
*natural penicillin and aminopenicillin don’t cover MSSA
*Treatment duration for oral: 7 days
- Selection of antimicrobial and regimen
Impetigo and Ecthyma
Discuss the CULTURE-DIRECTED antibiotic selection for Impetigo and Ecthyma (if Staph aureus)
Impetigo - Staph or Strep
Ecthyma - GAS
Culture directed (MSSA):
- PO Cephalexin 500mg q6h
- PO Cloxacillin 500mg-1g q6h
*Treatment duration for oral: 7 days
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Mainstay of treatment is _________
Incision and drainage
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
When is adjunctive systemic antibiotics required?
- Unable to drain completely
- Lack of response after drainage
- Extensive disease involving several sites
- Extremes of age
- Immunosuppressed
- Signs of systemic illness (SIRS: temp >38 or <36, HR >90, RR >24, WBC >12 or <4)
- IV antibiotics for severe disease
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Discuss the treatment for MILD common purulent cause (S. aureus)
Purulent - mainly S. aureus (some beta hemolytic, gram negative and anaerobe if skin abscess involving perioral, perirectal, vulvovaginal area)
Mild infection: incision and drainage, warm compress
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Discuss the antibiotic selection for MODERATE common purulent cause (S. aureus)
- Define MODERATE purulent
Purulent - mainly S. aureus (some beta hemolytic, gram negative and anaerobe if skin abscess involving perioral, perirectal, vulvovaginal area)
Moderate (w systemic symptoms): I&D + oral antibiotics
- PO Cephalexin 500mg q6h
- PO Cloxacillin 500mg-1g q6h
- PO Clindamycin 300-450mg q6h (if penicillin allergy)
*Treatment duration: 5-10 days
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Discuss the antibiotic selection for SEVERE common purulent cause (S. aureus)
- Define SEVERE purulent
Purulent - mainly S. aureus (some beta hemolytic, gram negative and anaerobe if skin abscess involving perioral, perirectal, vulvovaginal area)
Severe - with severe systemic signs, failed I&D
Severe: I&D + IV antibiotics
- IV Cefazolin 1-2g q8h
- IV Cloxacillin 500mg-1g q4-6h
- IV Clindamycin 600mg q8h
- IV Vancomycin 15mg/kg q8-12h (if allergic to everyone else, or if pt has hospital associated risk factors for HA-MRSA, or pt come from another country that may have CA-MRSA)
*Treatment duration: 5-10 days
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Discuss the antibiotic selection if pt might have MRSA
Purulent - mainly S. aureus (some beta hemolytic, gram negative and anaerobe if skin abscess involving perioral, perirectal, vulvovaginal area)
Empiric (MRSA) - if pt has hospital associated risk factors for HA-MRSA, or pt come from another country that may have CA-MRSA
Less severe:
- Co-trimoxazole (PO 960mg bid, IV 5mg/kg q8h)
- Doxycyline (PO 100mg bid)
- Clindamycin (PO 300-450mg q6h, IV 600mg q8h)
More severe:
- IV Vancomycin 15mg/kg q8-12h
- IV Daptomycin 4-6mg/kg q24h
- IV Linezolid 600mg q12h
*Treatment duration: 5-10 days
- Selection of antimicrobial and regimen
Purulent (Furuncle, Carbuncle, Skin abscesses, Purulent Cellulitis)
Discuss the antibiotic selection if pt might have gram negative or anaerobes
Purulent - mainly S. aureus (some beta hemolytic, gram negative and anaerobe if skin abscess involving perioral, perirectal, vulvovaginal area)
Empiric (gram-negative, anaerobes)
- PO Amoxicillin-Clavulanate 625mg TDS or 1g BD
- IV Amoxicillin-Clavulanate 1.2g q6-8h
*Treatment duration: 5-10 days
- Selection of antimicrobial and regimen
Non-purulent (Erysipelas, non-purulent Cellulitis)
Discuss the antibiotic selection in MILD non-purulent SSTIs
- Define MILD non-purulent
- What to cover?
Non-purulent - Beta-hemolytic streptococcus, usually Strep. Pyogenes (S. aureus less frequent, Pseudomonas with water exposure)
Mild (no systemic signs of infection): cover Strep Pyogenes
- PO Penicillin V 500mg q6h
- PO Cephalexin 500mg q6h
- PO Cloxacillin 500mg-1g q6h
- PO Amoxicillin 500mg-1g q8h
- PO Clindamycin 300-450mg q6h (Penicillin allergy)
*Duration: 5-10 days, 14 days if immunocompromised
- Selection of antimicrobial and regimen
Non-purulent (Erysipelas, non-purulent Cellulitis)
Discuss the antibiotic selection if MODERATE non-purulent SSTIs
- Define MODERATE non-purulent
- What to cover?
Non-purulent - Beta-hemolytic streptococcus, usually Strep. Pyogenes (S. aureus less frequent, Pseudomonas with water exposure)
Moderate (w systemic signs of infection, some purulence): include MSSA cover, may initiate IV alr
- IV Cefazolin 1-2g q8h
- IV Clindamycin 600mg q8h (Penicillin allergy)
*Duration: 5-10 days, 14 days if immunocompromised
- Selection of antimicrobial and regimen
Non-purulent (Erysipelas, non-purulent Cellulitis)
Discuss the antibiotic selection if SEVERE non-purulent SSTIs
- Define SEVERE non-purulent
- What to cover?
Non-purulent - Beta-hemolytic streptococcus, usually Strep. Pyogenes (S. aureus less frequent, Pseudomonas with water exposure)
Severe (w systemic signs of infection, failed oral therapy, or immunocompromised): include broader coverage and explore possibility of necrotizing infections
=> Cover gram -ve, anaerobe, pseudomonas
- IV Piperacillin/Tazobactam 4.5g q6-8h (cover gram +ve, gram -ve, anaerobes)
- IV Cefepime 2g q8h (cover gram +ve, gram -ve)
- IV Meropenem 1-2g q8h (cover gram +ve, gram -ve, anaerobes, ESBL)
*Duration: 5-10 days, 14 days if immunocompromised
- Selection of antimicrobial and regimen
Non-purulent (Erysipelas, non-purulent Cellulitis)
Discuss the antibiotic selection if SEVERE non-purulent SSTIs if there are MRSA risk factor (what to add on?)
Non-purulent - Beta-hemolytic streptococcus, usually Strep. Pyogenes (S. aureus less frequent, Pseudomonas with water exposure)
Severe (w systemic signs of infection, failed oral therapy, or immunocompromised): include broader coverage and explore possibility of necrotizing infections
ADD
- IV Vancomycin 15mg/kg q8-12h
- IV Daptomycin 4-6mg/kg q24h
- IV Linezolid 600mg q12h (If MRSA risk factor)
*Duration: 5-10 days, 14 days if immunocompromised
- Selection of antimicrobial and regimen
What are some non-pharmacological management for non-purulent SSTIs?
- Ensure rest and limb elevation (drainage of edema, inflammatory substances)
- Treat underlying conditions (e.g., tinea pedis, skin dryness, limb edema)
- Goal and monitoring therapeutic response for SSTI
Resolution of S&S
- Improvement by 48-72h after initiation (resolution not necessary)
- No progression of lesion or development of complication
- Switch to oral when pt is better
- If pt does not respond within 2-3 days, reassess indication and choice of antibiotics
Bacteriological Clearance
- Repeat culture not required for pt who responded
Absence of ADRs and allergies
Discuss the use of topical antibiotics in SSTI
Controversial
Most mild cases are self-limiting and would not require antibiotics
Severe cases require oral/IV antibiotics
Local wound care is central in treatment
Topical antibiotic may add cost and ADR
What is Mupirocin coverage, and what is it used for?
Mupirocin Coverage
- highly effective against aerobic gram positive cocci, especially S. aureus (bactericidal at 2% ointment)
- not effective against enterococci and gram negatives
Mupirocin Use
- Nasal staphylococcal carriage
- Impetigo (mild limited lesions) - BID x5d
Mupirocin resistance in MRSA is a major concern
- In hospital, reserved for MRSA decolonization and superficial infection (e.g., hemodialysis catheter exist site infection)
