Skin and Soft Tissue Infection Flashcards
Impetigo refers to
infection of the epidermis
Erisypelas refers to
infection of the epidermis/upper dermis
Cellulitis refers to
infection of the subcutaneous layer
Necrotising fasciitis refers to
infection of the fascia
What factors should be considered when assessing a soft tissue infection?
Site Organism Host Predisposing factors Environment
Important predisposing factors for soft tissue infections
Diabetes mellitus Immunosuppression Renal failure Milord's disease Predisposing skin conditions
Most common causative organism of impetigo
Staph aureus
Presentation of impetigo
Multiple vesicular lesions on an erythematous base
Golden crusting characteristic
Tends to occur on exposed areas of body
Second most common causative organism of impetigo
Strep pyogenes
Predisposing factors of impetigo
Skin abrasions Minor trauma Burns Poor hygiene Insect bites Chickenpox Eczema Atopic dermatitis
Treatment of impetigo
Small areas treated with topical antibiotics alone, targeting mainly gram positive
Large areas treated with topical and oral antibiotics e.g. flucloxacillin
Presentation of erysipelas
Raised erythematous areas Commonly affect face and limbs Painful red area Associated fever Regional lymphadenopathy and lymphangitis Distinct elevated borders
Most common causative organism of erysipelas
Strep pyogenes
Predisposing factors to erysipelas
Pre-exsting lymphoedema Venous stasis Obesity Paraparesis Diabetes mellitus
Recurrence rate of erysipelas
30% within 3 years
What percentage of erysipelas affects the lower limbs and face?
70-80% lower limbs
5-25% face
Presentation of cellulitis
Diffuse skin infections involving deep dermis and subcutaneous fat
Spreading erythematous area with no distinct borders
Fever
Systemically unwell
Causative organisms of cellulitis
Staph aureus
Strep pyogenes
When should gram negative organisms be considered as a cause of cellulitis?
Diabetic patients
Febrile neutropenic patients
Particularly if not improving
Predisposing factors of cellulitis
Diabetes mellitus Tinea pedis Lymphoedema Lymphangitis Lymphadenitis
Treatment of erysipelas and cellulitis
Combination of anti-staph and anti-strep antibiotics
Usually penicillin or vancomycin and doxycycline
Admission for IV antibiotics and rest if extensive disease
Follicular infections
Folliculitis
Furunculosis
Carbuncle
Presentation of folliculitis
Well circumscribed pustular infection of a single hair follicle
Small red papules
May occur in clusters, typically on head, back, buttocks and extremities
Central area of purulence
Most common causative organism of folliculitis
Staph aureus
What is furunculosis?
Inflammatory infection of a single hair follicle that extends deep into the dermis and subcutaneous tissue
Areas affected by furunculosis
Moist, hairy, friction prone areas
Most common causative organism of furunculosis
Staph aureus
Risk factors of furunculosis
Obesity Diabetes mellitus Atopic dermatitis Chronic kidney disease Corticosteroid use
What is a carbuncle?
Infection which has extended to involve multiple furuncles
Presentation of carbuncle
Large abscess involving multiple adjacent hair follicles
Multiseptated abscesses
Purulent material expressed from multiple sites
May drain spontaneously
Areas commonly affected by carbuncles
Back of neck
Posterior trunk
Thighs
Major predisposing factor for carbuncles
Diabetes mellitus
Treatment of folliculitis
No treatment or topical antibiotics
Treatment of furunculosis
No treatment or topical antibiotics
Oral antibiotics if failure to improve with topical
Treatment of carbuncle
Admission
Surgery
IV antibiotics
Presentation of necrotising fasciitis
Rapid onset Sequential development of erythema, extensive oedema and severe unremitting pain Haemorrhagic bullae Skin necrosis Crepitus Anaesthesia at site of infection
Systemic features of necrotising fasciitis
Fever Hypotension Tachycardia Delirium Multi-organ failure
Causative organism of type 1 necrotising fasciitis
Mixed aerobic and anaerobic infections Strep Staph Enterococci Gram negative bacilli Clostridium
Treatment of type 1 necrotising fasciitis
Broad spectrum Benzapenicillin for strep Flucloxacillin for staph Gentamicin for gram negatives Clindamycin to aid action of benza and fluclox Metronidazole for anaerobes
Causative organism of type 2 necrotising fasciitis
Monomicrobial
Usually associated with strep pyogenes
Predisposing factors of type 2 necrotising fasciitis
Diabetes mellitus Surgery Trauma Peripheral vascular disease Skin popping
Presentation of type 2 necrotising fasciitis
Rapid onset Redness followed by oedema and severe pain Hypotension Systemic features Multi-organ failure
Treatment of type 2 necrotising fasciitis
Cannula Fluids to raise BP Antibiotics - flucloxacillin, gentamicin, clindamycin Surgery - removal of dead tissue Surgical review
Overall mortality of type 2 necrotising fasciitis
17-40%
What is pyomyositis?
Purulent infection deep within striated muscles, often manifesting as an abscess
Sites affected by pyomyositis
Multiple sites involved in 15%
Thigh, calf, arms, gluteal region, chest wall, psoas muscle
Presentation of pyomyositis
Pain
Fever
Woody induration of affected muscle
Predisposing factors of pyomyositis
Diabetes mellitus HIV Immunocompromised IVDA Rheumatological disease Malignancy Liver cirrhosis
Commonest cause of pyomyositis
Staph aureus
Other organisms may be involved, including gram positive, gram negative, TB bacteria and fungi
Treatment of pyomyositis
Drainage and antibiotics depending on gram stain and culture results
Presentation of septic bursitis
Commonly affects olecranon and patellar bursae
Infection normally spread to bursae from adjacent skin infection
Peribursal cellulitis, swelling and warmth
Fever and pain on movement
Common causative organism of septic bursitis
Staph aureus
more rarely caused by mycobacteria and brucella
Diagnosis of septic bursitis
Based on aspiration of the fluid
Predisposing factors of septic bursitis
Rheumatoid arthritis Alcoholism Diabetes mellitus IVDA Immunosuppression Renal insufficiency
What needs to be excluded in the differential diagnosis of septic bursitis?
Septic arteritis - this requires immediate treatment
What is infectious tenosynovitis?
Infection of the synovial sheets that surround tendons
Area most commonly affected by infectious tenosynovitis
Flexor synovial sheets around tendons in the hand
Most common inciting event of infectious tenosynovitis
Penetrating trauma
Most common causative organism of infectious tenosynovitis
Staph aureus
Strep pyogenes
Causative organism of chronic infectious tenosynovitis
Mycobacteria or fungi
Presentation of infectious tenosynovitis
Erythematous fusiform swelling of the finger
Finger held in semi-flexed position
Tenderness over length of tendon sheet
Treatment of infectious tenosynovitis
Urgent review by hand surgeon
Surgery to relieve pressure
Empiric antibiotics
Toxin-mediated cutaneous infections are often due to
super antigens
How do pyogenic exotoxins work?
They don’t activate the immune system via normal contact between antigen presenting cells and T cells, they bypass this and attach directly to T cell receptors causing huge cytokine release
Most common cause of toxin-mediated cutaneous infections
Staph aureus TSST1, ETA and ETB
Strep pyogenes TSST1
What does toxic shock syndrome toxin 1 cause (TSST1) and how does it present?
Toxic shock syndrome
Presents as fever, rash, hypotension and organ failure
What do exfoliative toxins A and B cause and how does it present?
Staphylococcal scalded skin syndrome
Widespread bullae and skin exfoliation
What does Panton-Valentine leukocidin toxin cause?
Recurrent boils and haemorrhagic pneumonia in children and young adults
Diagnostic criteria for staphylococcal toxic shock syndrome
Fever
Hypotension
Diffuse macular rash
Three of the following involved; liver, blood, kidneys, 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
What is streptococcal toxic shock syndrome almost always associated with?
Presence of strep in a deep-seated infection e.g. erysipelas or necrotising fasciitis
Mortality rate of staph TSS vs strep TSS
Streptococcal TSS 50% mortality
Staphylococcal TSS 5% mortality
Treatment of toxic shock syndrome
Remove offending agents IV fluids Inotropes Antibiotics IV immunoglobulins
Risk factors of venflon-associated infections
Continuous IV infusion > 24 hours
Cannula in situ > 72 hours
Cannula in lower extremity
Neurological and neurosurgical problems
Causative organisms of venflon-associated infections
MMSA
MRSA
What can bacteraemia associated with venflon-associated infections cause?
Endocarditis
Osteomyelitis
Treatment of venflon-associated infections
Prevention
Removal of cannula
Antibiotics
Presentation of IV catheter associated infections
Normally starts as local STT inflammation, progressing to cellulitis and tissue necrosis
Associated bacteraemia
Treatment of IV catheter associated infections
Remove cannula
Express any pus from thrombophlebitis
Antibiotics 14 days
Echo
Prevention of infections in patients with peripheral venous cannulae
Do not leave an unused cannula Do not insert a cannula unless it is being used Change cannula every 72 hours Monitor for thrombophlebitis Practice aseptic technique
Risk factors of surgical site infections
Diabetes
Smoking
Obesity
Malnutrition
Procedural risk factors for surgical site infection
Shaving site of surgery the night prior to procedure Improper pre-operative skin preparation Improper antimicrobial prophylaxis Break in sterile technique Inadequate theatre ventilation Perioperative hypoxia
Causative organism of surgical site infection
Can be caused by any organism
Description of class 1 surgical site infection
Clean wound infection
- Respiratory, alimentary, genital and urinary systems not entered
- Infection in a surgical site that is sterile e.g. joint operations
- Normally due to invasive organisms e.g. staph aureus
Description of class 2 surgical site infection
Clean contaminated wound
- respiratory, alimentary, genital or urinary system entered but no unusual contamination
Description of class 3 surgical site infection
Contaminated wound
- infections at a surgical site that is either already contaminated at the start of surgery or is contaminated during surgery e.g. due to perforation in abdominal surgery
Description of class 4 surgical site infection
Infected wound
- existing clinical infection
Diagnosis of surgical site infection
Send pus/infected tissue for culture
Avoid superficial swabs
Consider unlikely pathogen if obtained from sterile site
Target likely organisms
