Lecture 12: Skin and Soft Tissue Flashcards
what is impetigo?
- superficial skin infection
- multiple vesicular lesions on an erythematous base
- golden crust is highly suggestive of this diagnosis
what organisms cause impetigo?
- most commonly due to staph. aureus
- less commonly strep. pyogenes
impetigo treatment
- small areas can be treated with topical antibiotics alone
- large areas need topical treatment and oral antibiotics (e.g. flucloxacillin)
clinical presentation of Erysipelas
- infection of the upper dermis
- painful, red area (no central clearing)
- associated fever
- regional lymphadenopathy and lymphangitis
- typically has distinct elevated borders
Erysipelas is most commonly due to which organism?
Strep pyogenes
Cellulitis clinical presentation
- diffuse skin infection involving deep dermis and subcutaneous fat
- presents as spreading erythematous area with no distinct borders
- fever is common
- regional lymphadenopathy and lymphangitis
- possible source of bacteraemia
most likely organisms causing cellulitis are?
strep pyogenes
staph aureus
which predisposing factors can increase risk of cellulitis?
- diabetes mellitus
- tinea pedis
- lymphoedema
what is the treatmnt for Erysipelas and Cellulitis?
- a combo of anti-staphylococcal and anti-streptococcal antibiotics
- in extensive disease, admission for intravenous antibiotics and rest
list some hair-associated infections
- folliculitis
- furunculosis
- carbuncles
clinical presentation of folliculitis
- circumscribed, pustular infection of a hair follice
- up to 5mm in diameter
- presents as small red papules
- central area of purulence that may rupture and drain
most common organism causing folliculitis?
- staph aureus
clinical presentation of furunculosis
- commonly referred to as boils
- single hair follice-associated inflammatory nodule extending into dermis and subcutaenous tissue
- usually affected moist, hair, friction-prone areas of body (face, axilla, neck and buttocks)
- may spontaneously drain purulent material
most common organism causing furunculosis?
stap aureus
furunculosis risk factors
- obesity
- diabetes mellitus
- CKD
- corticosteroid use
Carbuncle clinical presentation
- occurs when infection extends to involve multiple furuncles
- often located back of neck, posterior trunk or thigh
- multiseptated abscesses
- purulent material may be expressed from multiple sites
- constitutional symptoms present
treatment of folliculitis, furunculosis and carbuncles?
- folliculitis: no treatment or topical abx
- furunculosis: no treatment or topical abx. If not improving oral abx may be necessary.
- carbuncles: often require hospital admission, surgery and IV abx
necrotising fasciitis risk factors
- diabetes mellitus
- surgery
- trauma
- peripheral vascular disease
- skin popping
what does type I necrotising fasciitis refer to?
a mixed aerobic and anaerobic infection (diabetic foot infection, Fournier’s gangrene)
necrotising fasciitis typical organisms
- streptococci
- staphylococci
- enterococci
- gram-negative bacilli
- clostridium
what does type II necrotising fasciitis refer to?
a monomicrobial infection normally associated with strep pyogenes
necrotising fasciitis clinical presentation
- rapid onset
- sequential development of erythema, extensive oedema and severe, unremitting pain
- haemorrhagic bullae, skin necrosis and crepitus may develop
- systemic features: fever, hypotension, tachycardia, delirium and multi-organ failure
- anaesthesia at site of infection is highly suggestive of this disease
necrotising fasciitis management
- surgical review is mandatory
- imaging may help but could delay treatment
- abx should be broad-spectrum: flucloxacillin, gentamicin, clindamycin
pyomyositis clinical presentation
- purulent infection deep within striated muscle, often manifesting as an abscess
- infection is often secondary to seeding into damaged muscle
- can present with fever, pain and woody induration of affected muscle
- if untreated can lead to septic shock and death
pyomyositis predisposing factors
a rare and treatable bacterial infection that affects skeletal muscles
- diabetes mellitus
- HIV/immunocompromised
- IV drug use
- rheumatological diseases
- malignancy
- liver cirrhosis
pyomyositis causative organisms
- commonest is staph aureus
- other organisms can be involved including gram positive/negatives, TB and fungi
pyomyositis investigation
CT/MRI
pyomyositis treatment
- drainage with antibiotic cover depending on gram stain and culture results
what are bursae?
- small sac-like cavities that contain fluid and are lined by synovial membrane
- located subcutaneously between bony prominences or tendons
- facilitate movement with reduced friction
- most common include patellar and olecranon
septic bursitis clinical presentation
- infection of bursae often from adjacent skin infection
- peribursal cellulitis, swelling and warmth are common
- fever and pain on movement also seen
- diagnosis is based on aspiration of the fluid
septic bursitis predisposing factors
- adjacent skin infection
- rheumatoid arthritis
- alcoholism
- diabetes mellitus
- IV drug abuse
- immunosuppression
- renal insufficiency
most common causative organism of septic bursitis?
staph aureus infection
rare organisms include: gram-negative, mycobacteria, brucella
what is infectious tenosynovitis?
- infection of the synovial sheets that surround tendons
- flexor-muscle associated tendons and tendon sheats of the hand most commonly involved
most common organisms causing infectious tenosynovitis?
- staph aureus and streptococci
- chronic infections may be due to mycobacteria, fungi
how does infectious tenosynovitis commonly present?
- present with erythematous fusiform swelling of finger
- held in a semiflexed position
- tenderness over the length of the tendon sheat and pain with extension of finger are classical
infectious tenosynovitis treatment
- empiric antibiotics
- hand surgeon to review ASAP
pathogenesis of toxin-mediated syndromes
most often due to super antigens, what does it cause?
- often due to superantigens
- group of pyrogenic exotoxins
- do not activate immune system via normal contact between APC and T cells, instead, superantigens bypass this and attach directly to the T cell receptors activating up to 20% of the total pool of T cells.
- causes massive burst in cytokine release
- leads to endothelial leakage, haemodynamic shock, multi-organ failure and death.
what toxins does staph aureus release?
TSST1
ETA and ETB
what toxin does strep pyogenes release?
TSST1
what is the diagnostic criteria for staphylococcal toxic shock syndrome?
- fever
- hypotension
- diffuse macular rash
- three of the following organs involved: liver, blood, renal, GI, CNS, muscular
- isolation of staph aureus from mucosal or normally sterile sites
- production of TSST1 by isolate
- development of antibody to toxin during convalescence
describe streptococcal TSS
cause, mortality rate, treatment
- almost always associated with presence of streptococci in deap seated infections such as erysipelas or necrotising fasciitis.
- mortality rate much higher than staph 50% vs 5%
- need urgent surgical debridement of the infected tissues
what is the treatment for TSS?
- remove offending agent e.g. tampon
- IV fluids
- inotroped
- antibiotics
- IV immunoglobulins
what is staphylococcal scalded skin syndrome and how does it present?
- infection due to a particular strain of staph aureus producing the exfoliative toxin A or B
- characterised by widespread bullae and skin exfoliation
- usually occurs in children but rarely in adults as well
staphylococcal scalded skin syndrome treatment
IV fluids
antimicrobials
what can panton-valentine leucocidin toxin cause?
SSTI
haemorrhagic pneumonia
IV catheter associated infections clinical presentation
- nosocomial infection
- normally starts as local SST inflammation progressing to cellulitis and even tissue necrosis
- common to have an associated bacteraemia
risk factors for IV-catheter associated infections
- continuous infusion > 24 hours
- cannula in situ > 72 hours
- cannula in lower limb
- patients with neurological/neurosurgical problems
most common causative organism for IV catheter associated infections?
staph aureus (MSSA and MRSA)
IV/catheter associated infections treatment
- treatment is to remove cannula
- express any pus from the thrombophlebitis
- antibiotics for 14 days
- echocardiogram
classification of surgical wounds from I to IV
- class 1: clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
- class 2: clean-contaminated wound (above tracts entered but no unusual contamination)
- class 3: contaminated wound (open, fresh accidental wounds or gross spillage from GI tract)
- class 4: infected wound (existing clinical infection, infection present before the operation)
list the causative organisms of surgical site infections
- staph aureus (incl. MSSA and MRSA)
- coagulase negative staphylococci
- enterococcus
- E.coli
- pseudomonas aeruginosa
- enterobacter
- streptococci
- fungi
- anaerobes
patient-associated risk factors for surgical site infections
- diabetes
- smoking
- obesity
- malnutrition
- concurrent steroid use
- colonisation with staph aureus
procedural risk factors associated with surgical site infections
- shaving of site night prior to procedure
- improper preoperative skin prep
- improper antimicrobial prophylaxis
- break in sterile technique
- inadequate theatre ventilation
- perioperative hypoxia
SSTIs that need urgent attention
- necrotising fasciitis
- pyomyositis
- toxic shock syndrome
- PVL infections
- venflon-associated infections
