Skin and soft tissue infections Flashcards
What is the most distinguishing clinical feature of Impetigo?
Golden crust - the vesicular lesions that form with the infection rupture and ooze substances that form golden crust
Predisposing factors for impetigo?
- Skin abrasions
- Minor trauma
- Burns
- Poor hygiene
- Insect bites
- Chickenpox
- Eczema
- Atopic dermatitis
Treatment of impetigo
Small areas can be treated with topical antibiotics alone
Large areas need topical treatment and oral antibiotics (ex flucloxacillin)
Most common causative organism in Erysipelas?
Strep pyogenes
Describe how an Erysipelas infection presents
- Infection of the upper dermis - typically has distinct elevated borders i.e you can feel where it starts and ends
- Painful, red area
- Associated fever and regional lymphadenopathy and lymphangitis
- 70-80% of cases involves the lower limbs, 5-20% affect the face
How would you treat Erysipelas?
A combination of anti-staphylococcal and anti-streptococcal antibiotics i.e flucloxacillin, clarithromycin or co-amoxiclav etc
In extensive disease, admission for intravenous antibiotics and rest
How would you treat Cellulitis?
1st line = flucloxacillin, clarithryomycin, co-amoxiclav
In extensive disease, admission for intravenous antibiotics and rest
What is cellulitis?
Diffuse infection of the skin and the soft tissues underneath (deep dermis and subcutaneous fat)
What are the most likely causative organisms for cellulitis? (3)
Staph aureus Strep pyogenes Strep dysgalactiae MRSA also can be a cause
How does cellulitis present?
- Presents as a spreading erythematous area with no distinct borders
- Fever is common
- Regional lymphadenopathy and lymphangitis
What are some common predisposing factors of cellulitis?
- DM
- Tinea pedis ‘athletes’ foot’
- Lymphoedema
What is folliculitis?
- An infection of one hair follicle that has not extended beyond
- Small red papules with purulent centre
- Benign
- Typically found on head, back, buttocks and extremities
What is furunculosis?
- This is otherwise known as a boil
- The infection has breached the hair follicle to extend to the surrounding areas
- Usually affects moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)
- May spontaneously drain purulent material
What are carbuncles?
- Known as an abscess of the skin – involves numerous hair follicles
- Often located back of neck, posterior trunk or thigh
- Purulent material may be expressed from multiple sites + systemic features
- Can require hospital admission, surgical drainage + IV antibiotics
What is the most common organism causing folliculitis and furunculosis?
Staph aureus
Is there any treatment for folliculitis or furunculosis?
No
Treatment of Carbuncles
Often require admission to hospital, surgery and IV antibiotics
What is necrotising faciitis?
One of the infectious diseases emergencies affecting the fascia (deepest part of the skin)
What can predispose you to necrotising fasciitis?
- DM
- Surgery
- Trauma
- Peripheral vascular disease
- Skin popping - injecting illicit drugs into the dermis or subcutaneous tissue with the goal of achieving slower absorption, decreased risk of overdose, or easier administration than with IV drug administration.
What is type 1 necrotising fasciitis? Give examples
- Type I refers to a mixed aerobic and anaerobic infection i.e. diabetic foot infection, Fournier’s gangrene
- Typical organisms include:-
- Streptococci
- Staphylococci
- Enterococci
- Gram negative bacilli
- Clostridium
What is type 2 necrotising fasciitis? And which organism is it normally associated with?
- Type II is monomicrobial
- Strep pyogenes
How does necrotising fasciitis present?
- Rapid onset
- Sequential development of erythema, extensive oedema and severe, unremitting pain
- Development of haemorrhagic bullae, skin necrosis and crepitus
- Systemic features include fever, hypotension, tachycardia, delirium and multiorgan failure
Management of necrotising fasciitis
- Surgical review is mandatory
- Antibiotics should be broad spectrum i.e. Flucloxacillin, Gentamicin or Clindamycin
- Mortality can be as high as 40%
What is pyomyositis?
- Purulent infection deep within striated muscle, often manifesting as an abscess
- Common sites include: Thigh, Calf, Arms, Gluteal region, Chest wall or Psoas muscle
How might pyomyositis present?
With fever, pain and woody induration of affected muscle (stiff/hardened muscle)
If pyomyositis is left untreated what can it lead to?
Septic shock and death
What organisms cause pyomyositis?
Staph A, TB and fungi also
How is pyomyositis treated?
Drainage with antibiotic cover depending on Gram stain and culture results
What is septic bursitis?
Bursae are small sac-like cavities that contain fluid and are lined by synovial membrane. They are found subcutaneously between bony prominences or tendons and help facilitate movement with reduced friction. These can become infected and this is often from adjacent skin infection
Diagnosis is based on aspiration of the fluid
Predisposing factors for septic bursitis? (6)
- Rheumatoid arthritis
- Alcoholism
- DM
- IV drug abuse
- Immunosuppression
- Renal insufficiency
What is infectious tenosynovitis?
- Infection of the synovial sheats that surround tendons
- Penetrating trauma often creates opportunity for Staph A and streptococci infection
Which tendons are most commonly involved in infectious tenosynovitis?
Flexor muscle-associated tendons and tendon sheats of the hand most commonly involved
How does infectious tenosynovitis present?
- Erythematous fusiform swelling of finger
- Tenderness over the length of the tendon sheat and pain with extension of finger are classical
How should infectious tenosynovitis be managed?
Empiric antibiotics
Hand surgeon to review ASAP
What is a toxin mediated syndrome?
Conditions/illnesses that are caused by the toxins that organisms produce They are often due to superantigens
What do superantigens do?
They bypass normal communication between antigen presenting cell and T cells. This means the T cell receptors will be activated straight away and there will be a massive burst in cytokine release and this leads to septic shock
How does the normal immune system deal with a pathogen?
The foreign organism is taken up by antigen presenting cell and it degrades the organism. The APC then presents the antigens to T cells which activate the production of antibodies by cytokines
Which organisms are strongly associated with toxin-mediated syndromes?
- Staph A - TSST1, ETA and ETB
- Strep Pyogenes - TSST1
How would a Staphylococcal Toxic shock syndrome present?
- Fever
- Hypotension
- Diffuse macular rash
- Multi-system organ involvement
- Isolation of Staph aureus from mucosal or normally sterile sites
- Production of TSST1 by isolate
- Development of antibody to toxin during convalescence
How would a Streptococcal Toxic shock syndrome present?
- MORE SERIOUS - mortality rate is much higher than staph
- Almost always associated with presence of Streptococci in deep seated infections such as erysipelas or necrotising fasciitis
- Treatment necessitates urgent surgical debridement of the infected tissues
How do you treat toxic shock?
- Remove offending agent (ex tampon) IV fluids
- Antibiotics
- IV immunoglobulins - to help fight infection - uncommon due to shortage
- Inotropes - sometimes used - targets the heart’s contractility
What sorts of things can cause toxic shock? (2)
- Tampon use
- Small skin infections due to staph Aureus secreting TSST1
Exfoliative toxin A or B causes which toxin induced infection?
Staphylococcal scalded skin syndrome This causes skin to peel off. Common in children
How do IV catheter associated infections normally start?
Normally starts as local skin and soft tissue inflammation progressing to cellulitis and even tissue necrosis Commonly forms a biofilm which then spills into bloodstream
Most common organism causing IV catheter infections
Staph A (MSSA and MRSA)
Treatment of an IV catheter associated infection
- Treatment is to remove cannula and express any pus from the thrombophlebitis
- Antibiotics for 14 days Prevention is more important
- Echo - if there is associated bacteraemia as there is potential that the infection has spread and caused endocarditis
How to prevent a IV catheter infection
- 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 4 classes of Surgical site infections?
Class 1 - clean wound Class 2 - Clean-contaminated wound Class 3 - contaminated wound Class 4 - infected wound
Causes of surgical site infections
Any organism but most common = Staph aureus - MSSA and MRSA
Patient associated risk factors for surgical site infections
DM Smoking Obesity Malnutrition Concurrent steroid use - immunosuppressed
Procedural 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
Look
Infections that need urgent attention:-
- Necrotising fasciitis
- Pyomyositis
- Toxic shock syndrome
- PVL infections
