Skin and Soft Tissue Infections Flashcards
What are the infections associated with the following depth of skin?
What are the causative organisms for impetigo, erysipelas, cellulitis and necrotising fascitis?
Impetigo - s. aureus (less commonly due to strep pyogenes)
Erysipelas - strep pyogens
Cellulitis - Strep pyogenes, staph aureus (uncommon), H. influenza (rare)
Necrotising fascitis (strep pyogenes or mixed bowel flora)
What are the signs of impetigo?
Superficial skin infection, multiple vascular lesions on an erythematous base
Golden crust is highly suggestive of this diagnosis
Which age group is impetigo common in?
Age 2-5 years of age
Where does impetigo normally occur?
Usually occurs on exposed parts of the body including face, extremities and scalp
What are predisposing factors for impetigo?
–Skin abrasions
–Minor trauma
–Burns
–Poor hygiene
–Insect bites
–Chickenpox
–Eczema
–Atopic dermatitis
What is the treatment for impetigo?
Small areas can be treated with topical antibiotics alone
Large areas need topical treatment and oral antibiotics (flucloxacillin)
Where does erysipelas affect?
Affects the upper dermis
What are the other features of erysipelas besides infeciton of the upper dermis?
Painful, red area (no central clearing)
Associated fever
Regional lymphadenopathy and lymphangitis
Typically has distinct elevated borders
Most commonly due to strep pyogenes
Where is erysipelas likely to occur?
Most cases involve the lower limbs (70-80%)
5-20% affect the face
- Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
- May involve intact skin
- High recurrence rate (30% within 3 years)
What layerof the skin does cellulitis affect?
It is a diffuse skin infection involving deep dermis and subcutaneous fat
How does cellulitis differ from erysipelas?
Cellulitis has no distinct elevated borders
What is the most likely causative organism for cellulitis?
Strep pyogenes and staph aureus
What are the symptoms that can occur in conjunction with cellulitis?
Fever
Regional lymphadenopthy and lymphangitis
Possible source of bacteraemia
What re the predisposing factors for cellulitis?
Diabetes mellitus
Tinea pedis
Lymphoedema
Patients can have lymphangitis and/or lymphadenitits
What is the treatment for erysipelas and celulitis?
- A combination of anti-staphylococcal and anti-streptococcal antibiotics
- In extensive disease, admission for intravenous antibiotics and rest
What are the hair assocaited infections?
- Folliculitis
- Furunculosis
- Carbuncles
What is the difference between folliculitis, furuncles and carbuncles?
Folliculitis - erythema and a psutule in a single follicle
Furuncle - red tender nodule surrounding a follicle with one draining point
Carbuncle - abscess of several follciels with several drainage points
Describe the appearance of folliculitis
Small red papules
Central area of purulence that may rupture and drain
Up to 5 mm in diameter
What is the most common organism for folliculitis?
Staph aureus
It is a benign condition, constitutional symptoms not often seen
What tissue layer does furunculosis spread into?
Extends into the dermis and subcutaneous tissue
Where does furunculosis usualy affect?
•Usually affected moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)
What is the most common organism that can cause furunculosis?
Staph aureus is the most common organism
What are the risk factors for furunculosis?
–Obesity
–Diabetes mellitus
–Atopic dermatitis
–Chronic kidney disease
–Corticosteroid use
How are carbuncles formed?
When infection extends to involve multiple furuncles
Where are carbuncles found?
•Often located back of neck, posterior trunk or thigh
Describe the abscess found in a carbuncle
Multi-septated abscess
What is the treatment of hair associated infections?
Folliculitis - no treatment or topical antibiotics
Furunculosis - no treatment or topical antibiotics, if not improving oral antibiotics might be necessary
Carbuncles often require admission to hospital, surgery and intravenous antibiotics.
What are the predisposing factors to necrotising fasciitis?
•Predisposing conditions include
–Diabetes mellitus (diabetic foot infection is type 1)
–Surgery
–Trauma
–Peripheral vascular disease
–Skin popping
What is the difference between type 1 and type 2 necrotising fasciitis?
Type 1 - mixed infection (aerobic and anaerobic)
Type 2 - monomicrobial
What are the bacteria assocaited with necrotising fasciitis?
Typical organisms for type 1 include:
–Streptococci
–Staphylococci
–Enterococci
–Gram negative bacilli
–Clostridium
Type 2:
Strep pyogenes
What are the features of necrotising fasciitis?
- Rapid onset
- Sequential development of erythema, extensive oedema and severe, unremitting pain
- Haemorrhagic bullae, skin necrosis and crepitus may develop
- Systemic features include fever, hypotension, tachycardia, delirium and multiorgan failure
- Anaesthesia at site of infection is highly suggestive of this disease
What is the management of necrotising fasciitis?
- Imaging may help but could delay treatment
- Antibiotics should be broad spectrum
–Flucloxacillin
–Gentamicin
–Clindamycin
•Overall mortality ranges between 17-40%
What is pyomyositis?
Purulent infection deep within striated muscle, often manifesting as an abscess
Infection is often secondary to seeding into damaged muscle
What are the common sites of pyomyositis?
–Thigh
–Calf
–Arms
–Gluteal region
–Chest wall
–Psoas muscle
What is the clinical presentation for pyomyositis?
Can present with fever, pain and woody induration of affected muscle
What are the risks of pyomyositis?
Can lead to septic shock and death
What are predisposing factors for pyomyositis?
–Diabetes mellitus
–HIV/immunocompromised
–Intravenous drug use
–Rheumatological diseases
–Malignancy
–Liver cirrhosis
What are the causative organisms for pyomyositis?
Commonest cause is staph aureus, other organisms can be involved including gram positive/negatives, TB and fungi
What are the relevant investigations for pyomyositis?
Investigation using CT/MRI
What is the treatment for pyomyositis?
•Treatment is drainage with antibiotic cover depending on Gram stain and culture results
Where does septic bursisits most commonly occur?
Most commonly occurs in the patella and the olecranon
What are the predisposing factors for septic bursitis?
- Infection is often from adjacent skin infection
- Other predisposing factors include
–Rheumatoid arthritis
–Alcoholism
–Diabetes mellitus
–Intravenous drug abuse
–Immunosuppression
–Renal insufficiency
What are the clinical features of septic bursitis?
- Peribursal cellulitis, swelling and warmth are common
- Fever and pain on movement also seen
- Diagnosis is based on aspiration of the fluid
What are the infective organisms for septic bursitits?
Staph aureus
•Rarer organisms include
–Gram negatives
–Mycobacteria
–Brucella
What is infectious tenosynovitis?
Infection of the synovial sheaths that surround tendons
What are the most commonly associated tendons in infectious tenosynovitis?
•Flexor muscle-associated tendons and tendon sheats of the hand most commonly involved
What is the most common inciting agent for infectious tenosynovitis?
Penetrating trauma
What are the causative organisms for infectious tenosynovitis?
- Most common cause Staph aureus and streptococci
- Chronic infections due to mycobacteria, fungi
- Possibility of disseminated gonococcal infection
What are the clinical features of infectious tenosynovitis?
- 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
What is the treatment for infectious tenosynovitis?
- Empiric antibiotics
- Hand surgeon to review ASAP
What is the effect of superantigens on the immune system?
- Group of pyrogenic exotoxins
- Do not activate immune system via normal contact between APC and T cells
- Superantigens bypass this and attach directly to the T cell receptors activating up to 20% of the total pool of T cells instead of the normal 1/10,000
- Massive burst in cytokine release
- Leads to endothelial leakage, haemodynamic shock, multi-organ failure and ?death
What are the most likely causative organisms for toxin mediated syndromes?
- Mostly due to some strains of Staphylococcus aureus and Streptococcus pyogenes
- Staph aureus: TSST1 (this can cause toxic shock syndrome)
ETA and ETB
•Strep pyogenes: TSST1
What are the diagnostic criteria for toxic shock syndrome?
- 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 often lies in conjunction with streptococcal toxic shock syndrome?
•Almost always associated with presence of Streptococci in deep seated infections such as erysipelas or necrotising fasciitis
What is mortality rate of Strep TSS?
•Mortality rate is much higher than Staphylococcal (50% vs 5%)
What is treatment of TSS?
- Remove offending agent (ex tampon) - high absorbency tampons are assocaited with toxic shock syndromes - increased in 1980’s
- Intravenous fluids
- Inotropes (these alter the strength of musclular contractions)
- Antibiotics
- Intravenous immunoglobulins
Strepp TSS requires immediate debridement of the infected tissues
What causes staphylococcal scalded skin syndrome?
•Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B
Exfoliation is the removal of the dead skin cells on the skins outermost surface
Exfoliative toxin is called exfoliatin - Exfoliatin breaks down desmosomes. Specifically it is a proteas that cleave desmoglein -1 which normally holds in place the granulosum and the spinosum
What are the clinical features of staphylococcal scalded skin syndrome?
Characterised by widerspread bullae and skin exfoliation
Usually occurs in children but rareyl in adults as well
What are the features of panton-valentine leucocidin toxin?
Can causes SSTI (skin and soft tissue infection as well as haemorrhagic pneumonia)
- Tends to affect children and young adults
- Patients present with recurrent boils which are difficult to treat
Describe panton-velantine leucocidin toxin
Gamma haemolysin
What is the treatment for panton-valentine leucocidin toxin
•Treat with antibiotics that reduce toxin production
What are the stages of progression for intravenous - catheter associated infections?
Normally starts as inflammation
Then cellulitits
Then tissue necrosis
Common to have associated bacteraemia
What are the risk factors for intravenous catheter infections?
Continuous infusion (over 24 hours)
Cannula in situ (over 72 hours)
Cannula in situ lower limb
Patients with neurological/neurosurgical problems
What are the intravenous- catheter associated infections?
Most common organism is staph aureus (MSSA and MRSA)
Commonly forms biofilm which then spills into the blood stream
Can seed into other places such as endocarditis, osteomyelitis
Diagnosis made clinically or by positive blood cultures
What is the treatment for intravenous associated infections?
Remove cannula
Express any pus from the thrombophlebitis
Antibiotics for 14 days echocardiogram
Prevention is more important:
–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 I: Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
- Class II: Clean-contaminated wound (above tracts entered but no unusual contamination)
- Class III: Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
- Class IV: Infected wound (existing clinical infection, infection present before the operation)
What are the causes of surgical site infections?
- Staph aureus (incl MSSA and MRSA)
- Coagulase negative Staphylococci
- Enterococcus
- Escherichia coli
- Pseudomonas aeruginosa
- Enterobacter
- Streptococci
- Fungi
- Anaerobes
What are risk fctors for surgical site infections?
•Patient associated
–Diabetes
–Smoking
–Obesity
–Malnutrition
–Concurrent steroid use
–Colonisation with Staph aureus
Procedural:
–Shaving of site the night prior to procedure
–Improper preoperative skin preparation
–Improper antimicrobial prophylaxis
–Break in sterile technique
–Inadequate theatre ventilation
–Perioperative hypoxia
What is the diagnosis of surgical site infections?
- Importance of sending pus/infected tissue for cultures especially with clean wound infections
- Avoid superficial swabs – aim for deep structures
- Consider an unlikely pathogen as a cause if obtained from a sterile site (ex bone infection)
- Antibiotics to target likely organisms
(so culture, use deep sites, sterile site = unlikely pathogen, antibiotics)
What are the infections that need urgent attention?
–Necrotising fasciitis
–Pyomyositis
–Toxic shock syndrome
–PVL infections
–Venflon-associated infections
