Skin and Soft Tissue Infections Flashcards
What is the presentation of impetigo?
GOLDEN CRUST
Multiple vesicular lesions on erythematous base
Tends to be face, limbs
Children 2-5y
Where is impetigo an infection of?
Upper epidermis
What bacteria tend to cause impetigo?
Staph aureus (less commonly strep pyogenes)
What factors predispose to impetigo infection?
Broken skin basically
Skin abrasions, minor trauma, burns, poor hygiene, insect bites, chickenpox, eczema, atopic dermatitis
How do you treat impetigo?
Flucloxacillin
Where is erysipelas an infection of?
Upper dermis
What does erysipelas present like?
Pain, red area + fever + regional lymphadenopathy+ lymphangitis
ELEVATED BORDERS
Tends to be lower limbs
What tends to cause erysipelas?
Strep pyogenes
What can predispose to erysipelas?
Pre-existing lymphoedema, venous stasis, obesity, paraparesis, DM
Why is there high recurrence of erysipelas?
There is damage to the lymphatic system which never returns to its original function
Where does cellulitis affect?
Deep dermis and s/c fat
What does cellulitis present like?
Erythematous area with no distinct borders + fever + regional lymphadenopathy + lymphangitis (inflammation of lymphatic system)
What organism causes cellulitis most likely?
Strep pyogenes and staph aureus
Gram -ve infections in febrile neutropenia and DM
How might someone have ended up with cellulitis?
Portals of entry to skin (e.g. fungal foot infection) or infection secondary to systemic infection
What is the appearance of lymphangitis?
Red lines along line of lymphatic vessels
What conditions predispose to cellulitis?
DM, tinea pedis, lymphoedema
How do you treat erysipelas and cellulitis?
Flucloxacillin & benzyl penicillin (others: vancomycin/teicoplanin)
IV in extensive dx
What is folliculitis?
Circumscribed, pustular infection of a hair follicle
Up to 5mm
What does folliculitis present like?
Small red papules with central area of purulence that may rupture and drain
What typically causes folliculitis?
Staph aureus
What are furnucles?
Boils
Single hair follicle-associated inflammatory nodule (infection spreads into dermis and forms an abscess in s/c tissue)
Where do furnucles tend to occur?
Moist, hairy, friction prone areas (face, axilla, neck, buttocks)
What tends to cause furnucles?
Staph aureus
What are the risk factors for furnucles?
Obesity, DM, atopic dermatitis, CKD, corticosteroid use, shaving/waxing
What are carbuncles?
When infection extends to involve multiple furnucles
Multiseptated abscesses
+ high temp, low BP, signs and symptoms of sepsis
What does having a carbuncle normally mean?
Patient is immunocompromised
How do you treat carbuncles?
Systemic antibiotics
May req. surgery and admission to hospital
What is necrotising fasciitis?
Rapidly progressive infection resulting in extensive necrosis of deep tissue (s/c tissue, fascia, muscle) & systemic infection that can become lifethreatening
What can predispose to necrotising fasciitis?
DM, surgery, skin popping (IVDA into s/c fat), trauma, peripheral vascular disease
What are the two types of necrotising fasciitis?
Type 1 - mixed aerobic and anaerobic (diabetic foot infection, Fournier’s gangrene)
Type 2 - monomicrobial (strep pyogenes usually)
What are the typical organisms involved in type 1 necrotising fasciitis?
Strep, staph, enterococci, gram -ve bacilli, clostridium
What are the clinical features of necrotising fasciitis?
Rapid onset
Development of erythema, extensive oedema, severe, unremitting pain
Anaesthesia at site of injury
Haemorrhagic bullae, skin necrosis, crepitus
Systemic features: fever, hypotension, tachycardia, delirium, multi-organ failure
What can necrotising fasciitis progress to?
Gangrene, amputations, fatality
How do you treat necrotising fasciitis?
Surgical review
Broad spectrum antibiotics - flucloxacillin, gentamicin, clindamycin, benzyl penicillin & metronidazole)
Rx for sepsis
What is pyomyositis?
Purulent infection deep within striated muscle, often manifesting as pus filled absncess
What is pyomyositis secondary to?
Seeding into damaged muscle (i.e. infection is elsewhere and spreads via bloodstream to muscle)
Where are common sites for pyomyositis?
Thigh, calf, arms, gluteal region, chest wall, psoas
What is the presentation for pyomyositis?
Fever, pain, woody induration of affected muscle
can lead to septic shock and death
What predisposes to pyomyositis?
DM, HIV, immunocomp, IVDA, rheumatological dx, malignancy, liver cirrhosis
What organism tends to cause pyomyositis?
Staph aureus
Others: TB/fungi
How do you investigate pyomyositis?
CT/MRI
How do you Rx pyomyositis?
Drainage & antibiotics depending on gram stain and culture result
Where is septic bursitis most common?
Patellar and olecranon
How does septic bursitis tend to occur?
From adjacent skin infection
What factors predispose to septic bursitis?
RA, alcoholism, DM, IVDA, immunosuppression, renal insufficiency
What is the presentation of septic bursitis?
Area of redness over joint Loses definition around joint Peribursal cellulitis, swelling, war Fever Pain on movement
How do you differentiate septic bursitis from septic arthritis?
In septic arthritis unable to flex and extend the joint
How do you diagnose septic bursitis?
Aspiration of fluid
What organism tends to cause septic bursitis?
Staph aureus
Others: gram -ves, mycobacteria, Brucella
What is infectious tenosynovitis?
Infection of synovial sheaths surrounding the tendon
What tendons are most commonly involved in infectious tenosynovitis?
Flexor muscle assoc tendons & tendon sheaths of hands most commonly injured
What tends to be the initiating event in infectious tenosynovitis?
Penetrating trauma
What organisms most commonly cause infectious tenosynovitis?
Staph aureus and strep
Chronic infections due to mycobacteria and fungi
Rare cause: disseminated gonorrhoea infection
What is the presentation of infectious tenosynovitis?
Erythematous fusiform (tapers at both ends) swelling of finger Held in semi-flexed position (least amount of pain) Tenderness over length of tendon sheath and pain with extension of finger are classical
How do you treat infectious tenosynovitis?
Empirical antibx
Referral to hand surgeon
What is the pathophysiology behind toxin mediated syndromes?
Due to superantigens
Group of pyrogenic exotoxins
Do not activate immune system via normal contact between APC cells and T cells
Superantigens bypass this and attach directly to T cell receptors –> huge activation of T cells –> massive cytokine release –> endothelial leakage, haemodynamic shock, multiorgan failure & sometimes death
What are the strains that can cause toxin mediate syndromes?
Staph aureus: TSST1, ETA and ETB
Strep pyogenes: TSST1
Define toxic shock syndrome
Systemic inflammatory reaction caused by bacterial exotoxins
What can cause toxic shock syndrome?
E.g. tampon use, small skin infections due to staph aureus secreting TSST1
What is the diagnostic criteria for Staphylococcal TTS?
Fever, hypotension, diffuse macular rash (pink, blanching, all over body)
Three of liver, blood, renal, GI, CNS, muscular systems involved
Isolation of staph aureus from normally sterile sties
Production of TSST1 from isolate
Development of antibody to toxin during convalescence
What is streptococcal TTS always associated with?
Presence of streptococci in deep seated infections, e.g. NF/erysipelas
How do you treat streptococcal TTS?
Urgent surgical debridement of infected tissues
Mortality much higher than for staph TTS!!
How do you Rx TSS?
Remove offending agent, e.g. tampon IV fluids Inotropes Antibiotics IV Ig
What causes staphylococcal scalded skin syndrome?
Staph aureus producing the exfoliative A or B toxin
What is staphylococcal scalded skin syndrome characterised by?
Widespread bullae and skin exfoliation
How do you treat SSS?
IV fluids and antibiotics
What is Panton-Valentine Leucoidin toxin?
Toxin produced by some strains of staph aureus (gamma haemolysin that can be transferred from one strain of staph aureus to another)
What does PVL toxin cause?
Skin and soft tissue infections and haemorrhagic pneumonia
Patients present with recurrent boils which are difficult to treat
What are IV-catheter associated infections often presenting like?
Local skin and soft tissue inflammation, but may progress to cellulitis and even tissue necrosis
Common to have assoc. bacteraemia
What are risk factors for IV-catheter associated infections?
Continuous infusion >24h
Cannula in situ >72h
Cannula in lower limb
Patients with neurological/neurosurgical problems
What bacteria tends to cause IV catheter assoc. infections?
Staph aureus (MSSA/MRSA) Commonly forms biofilm
How do you diagnose IV catheter assoc. infections?
+ve blood cultures or clinical diagnosis
What are the presentations of IV catheter assoc. infections?
Area of thrombophlebitis going up
Veins feel really hard
Assoc. fever
How do you Rx IV catheter assoc. infections?
Remove cannula
Express any pus from thrombophlebitis
Antibx for 14 days
ECG
How can you prevent IV catheter assoc. infections?
Do not leave in unused cannulas Do not insert cannula unless req. Change cannula every 72h Monitor for thrombophlebitis Use aseptic technique when inserting cannula
What is the classification of surgical site infections?
1 - clean wound (resp, alimentary, genital, urinary systems not entered)
2 - clean wound (above tracts entered but no unusual contamination) 3 - contaminated wound (open, fresh, aciidental wounds or gross spillage from GI tract)
4 - infected wound (existing clinical infection, infection present before op)
What can cause surgical site infections?
Staph aureus (MSSA/MRSA) Coagulase -ve staph Enterococcus E. coli Pseudomonas aeruginosa Enterobacter Strep Fungi Anaerobes
What are risk factors for surgical site infections?
Diabetes Smoking Obesity Malnutrition Steroid use Colonisation with staph aureus Shaving of site prior to procedure Improper prep of skin preoperatively Improper antimicrobial prophylaxis Break in sterile technique Inadequate theatre ventilation perioperative hypoxia
How do you diagnose surgical site infections?
Sending pus/infected tissue for cultures
Avoid superficial swabs
Consider unlikely pathogen as cause if obtained from sterile site
