Skin And Soft Tissue Infection Flashcards
Describe the microbiome of the skin
- coagulase negative staphylococci
- corynebacterium sp.
- areas of skin with less acidic pH = S. aureus, S. pyogenes
- sweat + sebaceous glands = anaerobe P. Acnes
- fungi + mites
What characterises impetigo?
Golden encrusted skin lesions with inflammation localised to the dermis. Tends to be well circumscribed. Contagious.
What is the causative organism and treatment of impetigo?
- S. aureus
- usually mild + self limiting
- can treat with topical fusidic acid (well circumscribed) or systemic antibiotics if needed
What characterises tinea?
- superficial fungal infection in skin/nails
- very common (esp on feet - athletes foot)
- diagnosis made on skin scrapings
What are the causative organisms and treatment of tinea?
Most common causes = microsporum, epidermophyton, trichophyton
Treatment with topical therapy in non-severe cases involving skin alone = clotrimazole or terbinafine cream
Systemic therapy in severe cases involving hair/nails = terbinafine/itraconazole
What characterises a soft tissue abscess
- infection within the dermis/fat layers with development of walled off infection and pooled pus
- most commonly begins on lower limbs and tracks through the lymphatic system and may involve localised lymph nodes
What is the causative organism and treatment of soft tissue abscesses?
- usually B-haemolytic strep (group A strep + S. aureus most common)
- limited antibiotic penetration so usually surgical drainage is best
- no antibiotics needed if abscess fully drained and no surrounding cellulitis
Describe the Eron classification of cellulitis
Class I = no signs of systemic toxicity or uncontrolled comorbidities
Class II = systemically unwell or systemically well with comorbidity which can complicate or delay resolution of infection
Class III = significant systemic upset (confusion, tachycardia, hypotension) or unstable comorbidities that may interfere with response to treatment, or limb-threatening infection due to vascular compromise
- Class IV = the person has sepsis/severe life-threatening infection (eg. Necrotising fasciitis)
Describe the management of cellulitis
- Class I = primary care management with oral antibiotics
- Class II = short term hospitalisation and discharge on outpatient parenteral antibiotic therapy (OPAT) - ceftriaxone
- Class II/IV = urgent hospital admission
(Risk of life-threatening infection/facial cellulitis = urgent hospital admission)
What antibiotics are given for class I cellulitis?
Treatment to cover S. aureus + S. pyogenes
Oral:
1st line = flucloxacillin
2nd line = doxycycline, clarithromycin, clindamycin
(7 day treatment)
IV:
1st line = flucloxacillin
2nd line = vancomycin
(Can be switched to oral therapy in 48-72hrs)
What are the possible complications of cellulitis?
- local = severe tissue destruction
- distant = septic shock
Describe the cause and presentation of streptococcal toxic shock
- group A streptococcus
- primary infection within throat/skin/soft-tissue
- patients present with localised infection, fever and shock
- can have diffuse, faint rash over body/limbs
Describe the treatment of streptococcal toxic shock
- surgery (aggressively seek out abscesses for drainage)
- antibiotics = penicillin + clindamycin (reduce toxin production)
- severe cases = pooled human immunoglobulin
Describe the characteristics of necrotising fasciitis
- immediately life threatening soft tissue infection with deep tissue involvement
- rapidly progressive with extensive tissue damage requiring extensive surgical debridement
- surgical emergency
What are signs and symptoms of necrotising fasciitis?
- rapidly progressive
- pain out of proportion to clinical signs
- severe systemic upset
- presence of visible necrotic tissue
- late signs = fascial oedema + gas in soft tissue
Type I necrotising fasciitis
Polymicrobial
- usually complicates existing wounds, including surgical wounds
- microbiology usually shows a mix of gram positives, gram negatives and anaerobes
Type 2 necrotising fasciitis
Group A streptococcus
- usually occurs in previously healthy tissue, typically on limbs
- may follow a minor injury such as a scratch/sprain
- microbiology usually shows monobacterial infection with S. pyogenes only
Describe the treatment of necrotising fasciitis
Broad spectrum antibiotic therapy:
- flucloxacillin
- benzylpenicillin
- gentamicin
- clindamycin
- metronidazole
* surgical review
What are the common pathogens that can complicate bite wounds?
- staphylococci
- streptococci
- anaerobic organisms
- pasteurella (mammal bites)
- capnocytophagia (mammal bites)
Describe the treatment of bite wounds
Antibiotics:
1st line = co-amoxiclav
2nd line = doxycycline + metronidazole
Surgical treatment: early exploration + debridement of complications (eg. Tendon sheath infection)
Prophylactic treatment: antibiotics in high risk, tetanus, rabies (if cannot be excluded eg. Bat scratches/bites)
Describe the considerations required for hospital acquired infection
- vascular access sites should be checked (high risk for bacteraemia)
- MRSA infection
What are common infections for people who inject drugs?
- S. aureus predominates but infections often polymicrobial
- high rates of bacteraemia + disseminated infection (S. aureus bacteraemia, DVT + pulmonary abscesses triad)
*BBV testing required for every patient
What is PVL staphylococcus and its associations?
- virulence factor carried by some S. aureus
- associated with recurrent soft tissue boils and abscesses (over months/years)
- necrotising chest infections
What is the treatment of PVL staphylococcus?
- antibiotics (MRSA/MSSA, clindamycin to reduce toxin production)
- decolonisation therapy (+ household contacts) = topical chlorhexidine for skin/hair, nasal mupirocin ointment, washing of sheets/towels
Describe the characteristics, diagnosis + treatment of HSV
- type I = stomatitis (cold sore)
- type 2 = genital herpes (vesicular, may be painful)
- recurrent = virus latent in sensory nerve ganglia
- diagnosis = clinical, blood/vesicle fluid PCR, sometimes serology
- treatment = aciclovir (topical, oral, IV)
Describe characteristics, diagnosis + treatment of VZV (chickenpox)
- often self-limiting in children
- highly infectious (side room management) = contagious from day 8-21
- congenital abnormalities (if pregnant)
- causes pneumonitis in adults (more severe infection)
- diagnosis = vesicle fluid PCR
- treatment within 48hrs of symptoms = aciclovir PO/IV
Describe characteristics, diagnosis + treatment of VZV (shingles)
- reactivation of dormant VZV (dorsal root ganglia)
- dermatomal distribution
- isolate until last crop of vesicles crusted (reduces risk of transmission)
- treat only high risk patients = aciclovir
- pain management = NSAIDs, gabapentin
Describe burn injuries and its common pathogens
- microbial colonisation caused by loss of protective barrier and commensal organisms
- extent of burn injuries increases susceptibility to infection
- common organisms = group A strep, S. aureus (toxin production can be problem)
- opportunistic organisms = pseudomonas, bacillus
- complication = TSS (children), biofilm
What are the 3 zones in burns?
- coagulation
- stasis
- hyperaema
What is the treatment of burn wound infections?
- debridement of dead/severely infected tissue
- topical antiseptics/antimicrobials
- systemic antimicrobials
- tetanus (consider)
- prophylactic systemic antibiotics (not usually indicated)
