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🌱 來自: Huppert’s Notes
Skin and Soft Tissue Infections (SSTIs)🚧 施工中
Skin and Soft Tissue Infections (SSTIs)
Non-purulent and purulent cellulitis
• Pathophysiology: Cellulitis is an infection of the deeper layers of the dermis. It can be non-purulent or purulent (e.g., associated with pustules or a skin abscess)
• Pathogens: Gram-positive cocci, including:
- Non-purulent cellulitis: Beta-hemolytic streptococci, especially group A streptococci (e.g., S. pyogenes)
- Purulent cellulitis or abscess: S. aureus, including MRSA
• Clinical features:
- Unilateral warmth, tenderness, and erythema, often of a distal extremity. Bilateral involvement is rare.
- Fever, chills, or other systemic manifestations can be present.
- Abscess: Features of cellulitis + a focal collection of pus within the subcutaneous tissue
• Diagnosis: Cellulitis is a clinical diagnosis! No diagnostic tests are typically needed, but consider the following if the clinical picture is unclear and/or the patient is critically ill:
- Advanced imaging (e.g., CT with contrast) of an affected extremity if there is concern for a necrotizing skin and soft tissue infection or abscess
- Blood cultures in cases where there are notable systemic symptoms (e.g., fevers, rigors)
- Gram stain and culture of purulent fluid after incision and drainage of an abscess
- Superficial wound cultures are not useful in isolating organisms as they are often polymicrobial and do not reliably distinguish the causative organism from normal skin flora
- A skin biopsy may be helpful in cases that do not respond to appropriate therapy, in immunocompromised patients, and/or when the diagnosis of cellulitis is uncertain
• Treatment:
- Non-purulent cellulitis: Beta-hemolytic streptococci is the most common pathogen; MRSA is rarely implicated in non-purulent cellulitis (exceptions: penetrating trauma or MRSA colonization)
• Outpatient therapy:
- Cephalexin 500 mg PO QID (preferred) or clindamycin 300 mg PO TID (alternative)
- Duration of therapy: 5 days. If the patient is not responding to initial therapy after 72 hours, obtain imaging to rule out an underlying abscess, expand antibiotic coverage to include MRSA coverage, and consider alternative diagnoses.
• Inpatient therapy:
- Cefazolin 1 g IV q8 h. If not responding, broaden to vancomycin IV. Can narrow to a PO antibiotic when improving.
- Duration of therapy: Typically 5 days. If the patient is not responding to therapy, obtain imaging to rule out an underlying abscess, expand antibiotic coverage to include MRSA coverage (e.g., IV vancomycin), consider alternative diagnoses, and consider consulting ID and/or dermatology.
- Purulent cellulitis: Almost always caused by S. aureus, and often MRSA
• Outpatient therapy:
- If a drainable abscess is present: Patient should undergo incision and drainage (I&D). Clinical trials support the use of antibiotics after I&D, but many patients will improve without them, so the decision should be made on a case-by-case basis based on the risk and benefits for each individual patient
- If no abscess is present: Treat with empiric PO antibiotics that have MRSA coverage, such as:
• Trimethoprim-sulfamethoxazole 1 DS Tabs BID or
• Doxycycline 100 mg BID or
• Clindamycin 300 mg PO TID (alternative agent)
- Duration of therapy: 5 days. If the patient is not responding to initial therapy, obtain imaging to rule out an underlying abscess, consider inpatient admission for IV antibiotics, and consider alternative diagnoses.
• Inpatient therapy:
- IV vancomycin (preferred). Alternatives: IV daptomycin or linezolid. If the patient is responding to initial therapy, switch to a PO antibiotic (see options above).
- Duration of therapy: Typically 5 days from the start of vancomycin. If the patient is not responding to initial therapy, obtain imaging to rule out an underlying abscess, consider alternative diagnoses, and consider consulting ID and/or dermatology.
Necrotizing fasciitis
• Pathophysiology:
- Necrotizing fasciitis is an aggressive, morbid, and limb- and life-threatening infection within the deep layers of the skin
- Type 1 = Polymicrobial. Often both aerobic organisms (e.g., E. coli, Klebsiella spp.) and anaerobic organisms (Bacteroides spp., Clostridium spp., or Peptostreptococcus spp.).
- Type II = Monomicrobial. Group A strep (GAS) is the most common, less often beta-hemolytic streptococci or others
• Clinical features:
- Physical exam: Erythema (often more purple), pain out of proportion to degree of skin findings (e.g., “pain out of proportion to exam”), crepitus (because of subcutaneous gas production)
- Labs: Non-specific, but can have leukocytosis, hyponatremia, elevated inflammatory markers
• Diagnosis:
- Necrotizing fasciitis is a clinical diagnosis. Consult general surgery immediately if you suspect necrotizing SSTI
- Imaging can be helpful to further risk-stratify (look for soft tissue gas, although not a sensitive finding), but should not delay surgical consultation
- Clinical prediction tools: No reliable tools. The LRINEC score has previously been described and used but it has not demonstrated reliable sensitivity in follow-up studies
• Treatment:
- Empiric antibiotics should be started right away, but are ineffective alone. Possible empiric antibiotic regimen = vancomycin + ertapenem or piperacillin-tazobactam + clindamycin (because of its antitoxin effect and the Eagle effect, where it is more effective than PCN at high inoculation states)
- Emergent surgical debridement. Mortality approaches 100% without surgery.
Bite-related infections
• Pathogens: Consider pathogens in the animal’s mouth and pathogens on the patient’s skin:
- Oral flora of canines and felines includes Pasteurella spp., Capnocytophaga canimorsus (especially in dogs), as well as Staphylococcus spp. and Streptococcus spp.
- Cat bites are more morbid than dog bites and become infected more frequently (>80% of cat bites compared to ~5% of dog bites) because their teeth can penetrate more deeply
- The human oral flora includes Staphylococcus spp. and Streptococcus spp. as well as anaerobic organisms including Eikenella corrodens, Peptostreptococcus spp., Fusobacterium spp., and Prevotella spp.
- The majority of bite-related infections are polymicrobial
• Treatment:
- Antibiotic prophylaxis with amoxicillin-clavulanate 875 mg PO BID should be administered for 3–5 days in patients with any of the following: Laceration requiring stiches, bite wounds on the hand/face/genitals, underlying immunocompromise or advanced liver disease, edema of the infected area, a deep puncture, and/or a vascular graft near the bite site
- Consider surgical consultation if deep space infection, infection of the hand or face, underlying immunocompromise, crepitus on physical exam, and/or persistent signs of infection despite antibiotics
- Ensure tetanus vaccination is up-to-date
- Consider need for rabies post-exposure prophylaxis in dog and raccoon bites. Consult ID and contact the local health department