Skin and Soft Tissue Infections Flashcards
What must you consider in skin/soft tissue infections?
Site
Organism
Host
Environment
What host factors can affect skin infections?
DM
Immunosuppression
Renal failure
Milroy’s disease
Predisposing skin conditions
What is Milroy’s disease?
Congenital lymphoedema of the legs
What are the layers of skin?
Epidermis
Dermis
Hair Follicle
Subcutaneous fat
Fascia
Muscle
Which infections affect the epidermis?
Impetigo
Which infections affect the dermis?
Folliculitis
Eryspipelas
Cellulitis
Which infections affect the Subcutaneous fat?
Cellulitis
Erysipelas
Necrotising Fasciitis
How does impetigo present?
Superficial skin infection
Multiple vesicular lesions on a red base
Golden crust
What are the most common pathogens in impetigo?
Staph aureus
Strep pyogenes
What is this?
Impetigo
What is the epidemiology of Impetigo?
Children 2-5y/o
Highly infectious
Exposed parts of the body
How is impetigo treated?
Small areas = Topical antibiotics
Large areas = oral flucloxacillin
What is Erysipelas?
Painful infection of upper dermis
How does Erysipelas present?
Painful red area with no central clearing
Fever
Regional lymphadenopathy
Lymphangitis
Distinct, elevated borders
What is the most common causative pathogen of Erysipelas?
strep pyogenes
What is this?
Erysipelas
Erysipelas typically affects which parts of the body?
70-80% lower limbs
5-20% face
Areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, DM
What is the recurrence rate of Erysipelas?
30% in 3 years
What is Cellulitis?
•Diffuse skin infection involving deep dermis and subcutaneous fat
How does Cellulitis present?
Spreading erythematous area with no distinct borders
Fever
Regional lymphadenopathy/lymphangitis
What are the most common causative pathogens in Cellulitis?
Strep pyogenes
Staph aureus
Gram -ves (diabetics, febrile neutropaenics)
Cellulitis can cause what?
Bacteraemia
What is this?
Cellulitis
How is Cellulitis investigated?
Investigate for predisposing factors:
- DM
- Tinea pedis
- Lymphoedema
How is cellulitis and erysipelas managed?
Anti-staphylococcal and anti-streptococcal antibiotics
Potentially admission and IV antiB for severe disease
What are the most common hair-associated infections?
- Folliculitis
- Furunculosis
- Carbuncles
What is folliculitis?
Circumscribed, pustular infection of a hair follicle
How does Folliculitis present?
- Up to 5mm in diameter
- Present as small red papules
- Central area of purulence that may rupture and drain
Typically on Head, back, buttocks and extremities
What is the most common causative pathogen of Folliculitis?
Staph aureus
What is Furunculosis?
Boils - single hair follicle associated inflammatory nodule
Extension into dermis and subcutaneous tissue
Furunculosis typically affects which parts of the body?
Moist, hairy, friction prone areas
What is this?
Furunculosis
What is the most common causative pathogen of Furunculosis?
Staph aureus
What are the risk factors for Furunculosis?
–Obesity
–Diabetes mellitus
–Atopic dermatitis
–Chronic kidney disease
–Corticosteroid use
What is a Carbuncle?
Infection spreading to involve multiple furuncles
Multi-septated abscesses
Purulent material expressed from multiple sites
How does a Carbuncle present?
Back of neck, posterior trunk, thigh
Constitutional symptoms
What is this?
Carbuncle
How is furunculosis treated?
Oral antibiotics if not improving by itself
How are Carbuncles treated?
Surgery
Intravenous antibiotics
What are the predisposing conditions of Necrotising fasciitis?
–Diabetes mellitus
–Surgery
–Trauma
–Peripheral vascular disease
–Skin popping
– IVDA
What are the main types of Necrotising fasciitis?
Type 1 - mixed aerobic/anaerobic
Type 2 - monomicrobial
What organisms are involved with type 1 Necrotising fasciitis?
–Streptococci
–Staphylococci
–Enterococci
–Gram negative bacilli
–Clostridium
What organisms are involved with type 2 Necrotising fasciitis?
Strep pyogenes
What is this?
Type 2 necrotising fasciitis
How does type 2 necrotising fasciitis present?
Cellulitis with extreme pain - opiates
Haemorrhagic bullae
What is implied by a haemorrhagic bullae?
Necrotising fasciitis
or
Cellulitis with ANTICOAGULANTS
How does Necrotising fasciitis present?
Rapid onset
Sequential erythema, oedema, severe pain
Haemorrhagic bullae
Skin necrosis
Fever, hypotension, tachycardia, multiorgan failure
How is Necrotising fasciitis assessed?
Surgical review - see if NF has penetrated the fascia
How is Necrotising fasciitis treated?
Broad spec. antibiotics
–Flucloxacillin
–Gentamicin
–Clindamycin
What mortality is associated with Necrotising fasciitis?
17-40%
What is pyomyositis?
Purulent deep infection in striated muscle - abscess
Multiple sites
What sites are commonly effected by Pyomyositis?
–Thigh
–Calf
–Arms
–Gluteal region
–Chest wall
–Psoas muscle
How does Pyomyositis present?
Fever, pain, induration of affected muscle
What complications are associated with untreated Pyomyositis?
Septic shock
Death
What predisposing factors are associated with Pyomyositis?
–Diabetes mellitus
–HIV/immunocompromised
–Intravenous drug use
–Rheumatological diseases
–Malignancy
–Liver cirrhosis
What is the most common pathogen in Pyomyositis?
Staph aureus
Gram+ve/-ves
TB
Fungi
How is Pyomyositis investigated?
CT/MRI
How is Pyomyositis managed?
Drainage
Antibiotics (depending on stain)
What are Bursae?
Small sac-like cavities that contain fluid in synovial membrane
Reduce friction in joints
What are the most common sites of septic bursitis?
Patellar
Olecranon
What is the cause of Septic bursitis?
Infection from adjacent skin site
What are the predisposing factors for Septic bursitis?
–Rheumatoid arthritis
–Alcoholism
–Diabetes mellitus
–Intravenous drug abuse
–Immunosuppression
–Renal insufficiency
How does Septic bursitis present?
Peribursal cellulitis
Swelling
Warmth
Fever
Pain on movement
How is Septic bursitis diagnosed?
Aspiration of fluid
What are the most common organisms in Septic bursitis?
Staph aureus
Gram -ves
Myocbacterium
Brucella
What is Infectious tenosynovitis?
Infection of synovial sheaths surrounding tendons
Which tendons are most commonly associated with Infectious tenosynovitis?
Flexor muscle associated tendons
Tendon sheaths around hand
What is the most common cause of Infectious tenosynovitis?
Penetrating trauma
Which pathogens are most commonly responsible for Infectious tenosynovitis?
Staph aureus
Streptcocci
What are the most common causes of chronic Infectious tenosynovitis?
Mycobacteria
Fungi
Disseminated gonoccal infection
How does Infectious tenosynovitis present?
Erythematous fusiform swelling of finger
Semiflexed position
Tenderness overlength of tendon sheath
Pain with extension
How is Infectious tenosynovitis treated?
Antibiotics
Hand surgeon review
What are the most common causes of toxin-mediated syndromes?
Superantigens (pyrogenic exotoxins)
How do superantigens work?
Bypass APC and attach directly to T-cell receptors
Massive burst in cytokine release
Endothelial leakage, haemodynamic shock, multiorgan failure
Which strains of Staphyloccus aureus are responsible for Toxin-mediated syndromes?
TSST1
ETA
ETB
Which strains of Streptococcus pyogenes are responsible for Toxin-mediated syndromes?
TSST1
What is the diagnostic criteria for Staphylococcal toxic shock syndrome?
Fever
Hypotension
- Fever
- Hypotension
- Diffuse macular rash
- Three of the following organs involved
(Liver, blood, renal, gatrointestinal, 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 associated with?
Deep seated infections:
Erysipelas
Necrotising fasciitis
What is the rate of mortality for Streptococcal TSS compared to Staphylococcal TSS?
Strep: 50%
Staph: 5%
How are toxic shock syndromes treated?
Surgical debridement of infected tissues
IV fluids
Inotropes
Antibiotics
IV immunoglobulins
What is Staphylococcal scalded skin syndrome?
Infection due to Staph aureus strains producing exfoliative toxin A or B
How does Staphylococcal scalded skin syndrome present?
Widespread bullae
Skin exfoliation
Children
How is Staphylococcal scalded skin syndrome managed?
IV fluids
Antimicrobials
What mortality is associated with Staphylococcal scalded skin syndrome?
3% children
Higher in adults
What is Panton-Valentine leucocidin toxin?
Gamma haemolysin
Transfers from one strain of Staph aureus to another
Panton-Valentine leucocidin toxin can cause what?
SSTI
Haemorrhagic pneumonia
Panton-Valentine leucocidin toxin affects which patients?
Children/young adults
How does Panton-Valentine leucocidin toxin present?
Recurrent, difficult to treat boils
How is Panton-Valentine leucocidin toxin treated?
Antibiotics that reduce toxin production
How do Intravenous-catheter associated infections present?
Starts with SST inflammation, progresses to cellulitis then tissue necrosis
Associated bacteraemia
What are the risk factors for Intravenous-catheter associated infections?
–Continuous infusion >24 hours
–Cannula in situ >72 hours
–Cannula in lower limb
–Patients with neurological/neurosurgical problems
What organisms are associated with Intravenous-catheter associated infections?
Staph aureus (MSSA/MRSA)
How does the pathogen act in Intravenous-catheter associated infections?
Staph aureus forms a biofilm - spills into blood stream
Can seed to other places
How is Intravenous-catheter associated infections diagnosed?
Blood cultures
How are Intravenous-catheter associated infections treated?
Remove cannula
Express andy pus
14 days antibiotics
Echocardiogram
(Prevention)
How are Intravenous-catheter associated infections prevented?
–Do not leave unused cannula
–Do not insert cannulae unless you are using them
–Change cannulae every 72 hours
–Monitor for thrombophlebitis
–Use aseptic technique when inserting cannulae
What are the classes of surgical wounds?
Class 1-4
- Clean wound
- Clean-contaminated wound
- Contaminated wound
- Infected wound
What is a class 1 surgical wound?
Clean wound - resp/alimentary/genital/urinary system not entered
What is a class 2 surgical wound?
Clean-contaminated wound: respiratory, alimentary, genital or infected urinary systems entered but not contaminated
What is a class 3 surgical wound?
Contaminated wound - Open, fresh accidental wound or gross spillage from GIT
What is a class 4 surgical wound?
Infected wound - infection present before operation
Name 3 bacterial causes of surgical site infections?
- Staph aureus
- Coagulase negative Staphylococci
- Enterococcus
- Escherichia coli
- Pseudomonas aeruginosa
- Enterobacter
- Streptococci
- Fungi
- Anaerobes
What are the patient associated risk factors for surgical site infections?
–Diabetes
–Smoking
–Obesity
–Malnutrition
–Concurrent steroid use
–Colonisation with Staph aureus
What are the procedural factor associated risk factors for surgical site infections?
–Shaving of site the night prior to procedure
–Improper preoperative skin preparation
–Improper antimicrobial prophylaxis
–Break in sterile technique
–Inadequate theatre ventilation
–Perioperative hypoxia
How are surgical site infections diagnosed?
Send pus/infected tissue for culture - esp. when wound clean
Avoid superficial swabs (go deep fam)
Consider unlikely pathogen if sterile site
Antibiotics
