Skin and Soft Tissue Infections Flashcards
Differentiate between impetigo and ecthyma
Impetigo is a superficial infection of skin characterized by pustules / vesicles progressing to crusting
Ecthyma is a deeper variant of vesicles/pustules that evolve into punched out ulcer
Define what is erysipelas
Erysipelas is a more superficial infection of skin involving lymphatics and are characterized by tender, erythematous plaque with well-demarcated borders
Define a furuncle and carbuncle
Furuncle is an infection of the hair follicle with small subcutaneous abscess
Carbuncles a collection of furuncles
What are some of the host defense mechanisms? Therefore, describe the pathogenesis of SSTI.
Host defense mechanism
1. Skin act as physical, chemical and immunological barrier.
2. Continuous renewal of epidermal layer –> shedding of keratocytes and skin microbiota
3. Sebaceous secretion: inhibit growth of bacteria and fungi
4. Normal commensal skin microbiome: prevent colonization and overgrowth of pathogenic strains
Disruption of normal host defenses leads to an overgrowth and invasion of skin and soft tissues by pathogenic microorganisms.
List some of the risk factors associated with SSTI
Disruption of skin barrier
- Traumatic: lacerations, recent surgery, burns, abrasions, crush injuries
- Non traumatic: ulcer, tinea pedis, toe web intertigo, chemical irritants
- Impaired venous and lymphatic drainage: sapheous vasectomy, obesity, chronic venous insufficiency
Conditions predisposing infections: DM, Cirrhosis, Neutropenia, HIV, Immunosuppressive and transplantation
History of cellulitis
What is some advice you can counsel a patient should they have any of the risk factors, to prevent SSTI?
Manage current predisposing risk factors (e.g. treat tinea pedis)
Prevent dry and cracked skin
Good foot care for DM patients to prevent wound and ulcers
Good wound care to maintain skin integrity by treating acute traumatic wounds
What is some advice you can counsel a patient should they have any of the risk factors, to prevent SSTI?
Manage current predisposing risk factors (e.g. treat tinea pedis)
Prevent dry and cracked skin
Good foot care for DM patients to prevent wound and ulcers
Good wound care to maintain skin integrity by treating acute traumatic wounds
Using the systematic approach, how do I confirm the presence of an SSTI infection?
Acknowledge the risk factors through history taking and checking for underlying disease; recent trauma, bites, burns and water exposure; animal exposure; travel history.
Diagnose with swab culture and blood culture
When is a blood culture indicated?
Severe cases with marked systemic signs of infection
Immunocompromised patients
Is swab cultures always necessary?
No. Mild superficial infections do not need a swab culture.
How should a swab culture be collected?
Deep in wound after surface is cleansed
Base of closed abscess
Curettage
What is a telltale sign that differentiates between an impetigo and ecthyma?
Impetigo have dried discharge forming honey crust on erythematous base and are well localised lesions
Ecthyma are lesions extending through epidermis and deep into dermis. A significant sign would be pruritus
What is the differences between erysipelas and cellulitis?
Erysipelas usually located in lower extremities of the upper dermis. They are painful plaques raised above skin and have well-demarcated edges
Cellulitis usually found in lower extremities and are non-elevated, acute and diffuse, can spread thus have poor demarcation. They are unilateral as well
Identify the type of pathogen associated with impetigo
Staphylococci
Streptococci
Identify the type of pathogen associated with ecthyma
Group A streptococcus
What are some nonpurulent SSTI?
Cellulitis
Erysipelas
Identify the type of pathogens associated with non-purulent SSTI
Group A Streptococcus
RARE: S.Aureus and Psuedomonas if have water exposure
What are some purulent SSTI?
Cellulitis
Skin abscess
Carbuncles
Furuncles
List the pathogens associated with purulent SSTI.
S.Aureus (mainly)
Group A Streptococcus
CA-MRSA (US) and HA-MRSA (US & SG)
What is the treatment and duration for mild, limiting impetigo? Why is the use of this agent generally not recommended?
Topical mupirocin BD for 5 days
Generally not needed because the condition is self-limiting. While it is effective against aerobic gram positive cocci, it is not effective against enterococci and gram negatives.
Also potential increase in resistance in MRSA
For impetigo and ecthyma, what is the empiric therapy and duration to initiate?
PO Cephalexin 500mg q6h / PO Cloxacillin 500mg - 1g q6h for 7 days
If a patient has beta lactam allergy, what is an alternative empiric therapy to consider for impetigo and ecthyma
PO Clindamycin 300-450mg q6h
Upon receiving AST results, what is the culture directed therapy for Staphylococcus impetigo and ecthyma?
PO Cephalexin 500mg q6h / PO Cloxacillin 500-1g q6h
Upon receiving AST results, what is the culture directed therapy for S.pyogenes impetigo and ecthyma?
PO Penicillin V 500mg q6h / PO Amoxicillin 500mg - 1g q8h
For purulent SSTI, how is an antibiotic therapy chosen?
Determine severity and route of treatment
Consider if empiric therapy is needed to cover the following
What is the severity classification and choice of treatment for purulent SSTI?
Mild: I&D
Moderate (have systemic signs of infection): I&D and oral antibiotics
- Cephalexin
- Cloxacillin
- Penicillin allergy: Clindamycin
Severe: requires IV antibiotics and I&D
- Cefazolin 1-2g q8h
- Cloxacillin 500mg - 1g q4-6h
- Clindamycin 600mg q8h
- Vancomycin 15mg/kg/d
If empiric therapy is needed to cover MRSA for purulent SSTI, what do I consider if the patient is in the US? What are some agents I can use?
Consider CA-MRSA
- Co-trimoxazole 960mg BD
- Doxycycline 100mg BD
- Clindamycin 300-450mg BD
What is an agent I can use to target MRSA risk in Singapore for purulent SSTI?
Vancomycin
Daptomycin
Linezolid
What empiric therapy can I consider for patients with Gram Negative and anaerobe risk factors?
Amoxicillin clavulanate 625mg TDS or 1g BD
What is the ideal duration of treatment for antibiotics for those with purulent SSTI?
5-10 days
When should I consider the need for antibiotics to treat SSTI?
Unable to drain completely
Lack of response to I&D
Extensive disease involving several sites
Extreme age
Immunosuppressed patients
Signs of systemic illness based on vital signs
What is the severity classification for nonpurulent SSTI?
Mild: No signs of systemic infection
Moderate: Signs of systemic infection and some purulence
Severe; Signs of systemic infection, unable to tolerate oral therapy and immunocompromised
How should I treat mild nonpurulent SSTI?
PO Penicillin V 500mg q6h
PO Cloxacillin 500mg - 1g q6h
PO Cephalexin 500mg q6h
What is an alternative agent to treat mild and moderate SSTI if patient is allergic to beta lactams?
PO Clindamycin 300-450mg q6h
How is moderate nonpurulent SSTI treatment different from that of mild SSTI?
Inclusion of MSSA coverage
What is an agent to start for moderate non purulent SSTI?
IV Cefazolin 1-2g q8h
What are some agents used to treat those with severe nonpurulent SSTI?
Piperacillin Tazobactam 4.5g q6-8h
Meropenem
Cefepime 2g q8h
How long is the duration of therapy for those with nonpurulent SSTI?
5-10 days
How long should I extend the duration of therapy for those who are immunocompromised and have nonpurulent SSTI?
14 days
How should I advice an outpatient in treating their nonpurulent SSTI at home?
Ensure rest and limb elevation to allow drainage of edema and inflammatory substances
Treat underlying cause of nonpurulent SSTi
What are some differential diagnosis of cellulitis?
Deep venous thrombosis
Calciphylaxis
Stasis dermatitis
Hematoma
Erythema migrans
