Skin and Soft Tissue Infections Flashcards
What things should be considered with skin and soft tissue infections?
- Site
- Organism
- Host
- Environment
What should be considered about the site of infection?
-Possible complications with specific sites (ex; abdo, face)
What should be considered about the organism causing infection?
Gram negative or gam positive
What should be considered about the infected host?
- Diabetes leading to neuropathy and vasculopathy
- Immunosuppression
- Renal failure
- Milroy’s disease (lymphatic system has not developed in specific part of the body, usually a limb)
- Predisposing skin conditions (ex; atopic dermatitis)
What should be considered about the environment with infection?
- Drug-resistant strains (MRSA)
- Drug interactions
- Drug allergies
What is impetigo?
A highly infection superficial skin infection
What is the presentation of impetigo?
- Multiple vesicular lesions on an erythematous base
- Golden crust is highly suggestive of this diagnosis
What organisms cause impetigo?
- Most commonly due to Staph aureus
- Less commonly Strep pyogenes
Where does impetigo usually affect?
Usually occurs on exposed parts of the body including face, extremities and scalp
Who usually gets impetigo?
Children aged 2-5
What are the 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 (ex flucloxacillin)
What is erysipelas?
Infection of the upper dermis with a high recurrence rate (30% withi 3 years)
How does erysipelas present?
- Painful, red area (no central clearing)
- Associated fever
- Regional lymphadenopathy and lymphangitis
- Typically has distinct elevated borders
What organisms is commonly responsible for erysipelas?
Strep. pyogenes
Where does erysipelas usually affect?
- 70-80% of cases involves the lower limbs
- 5-20% affect the face
- Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
What is cellulitis?
Diffuse skin infection involving deep dermis and subcutaneous fat
How does cellulitis present?
- Presents as a spreading erythematous area with no distinct borders
- Fever is common
- Regional lymphadenopathy and lymphangitis
What are the most likely organisms involved in cellulitis?
- Strep pyogenes
- Staph aureus
What are the predisposing factors for cellulitis?
- Diabetes mellitus
- Tinea pedis
- Lymphoedema
What is the treatment for erysipelas?
- A combination of anti-staphylococcal and anti-streptococcal antibiotics
- In extensive disease, admission for intravenous antibiotics and rest
What is the treatment for cellulitis?
- A combination of anti-staphylococcal and anti-streptococcal antibiotics
- In extensive disease, admission for intravenous antibiotics and rest
Give examples of hair associated infections.
- Folliculitis
- Furunculosis
- Carbuncles
What is folliculitis?
- A circumscribed, pustular infection of a hair follicle, up to 5mm in diameter
- Benign
How does folliculitis present?
- Present as small red papules
- Central area of purulence that may rupture and drain
- Absence of constitutional symptoms
Where does folliculitis typically occur?
Head, back, buttocks and extremities
What is the most common organism in folliculitis?
Staph aureus
What is furunculosis?
- Furuncles are commonly referred to as boils.
- Single hair follicle-associated inflammatory nodule which extends into the dermis and subcutaneous tissue
Where does furunculosis commonly affect?
Moist, hairy friction-prone areas of the body (face, axilla, neck and buttocks)
What can furuncles spontaneously do?
Drain purulent material
What is the most common organism in furunculosis?
Staph aureus
What are the risk factors for furunculosis?
- Obesity
- Diabetes mellitus
- Atopic dermatitis
- Chronic kidney disease
- Corticosteroid use
When does carbuncle usually occur?
When infection extends to involve multiple furuncles
Where do carbuncles usually occur?
Often on the back of the neck, posterior trunk or thigh
What do carbuncles present?
- Multiseptated abscesses
- May express purulent material from multiple sites
- Constitutional symptoms are common
What is the treatment for folliculitis?
No treatment or topical antibiotics
What is the treatment for furunculosis?
- No treatment or topical antibiotics
- Oral antibiotics may be necessary if no improvement
What is the treatment for carbuncles?
Often require admission to hospital, surgery and IV antibiotics
What is necrotising fasciitis?
An infectious disease emergency
Where can necrotising fasciitis affect?
Any site
What are the predisposing factors for necrotising fasciitis?
- Diabetes mellitus
- Surgery
- Trauma
- Peripheral vascular disease
- Skin popping
What is type 1 necrotising fasciitis?
Type I refers to a mixed aerobic and anaerobic infection (diabetic foot infection, Fournier’s gangrene)
What organisms are implicated in type 1 necrotising fasciitis?
- Streptococci
- Staphylococci
- Enterococci
- Gram negative bacilli
- Clostridium
What is type 2 necrotising fasciitis?
Monomicrobial infection
What organism is usually implicated in type 2 necrotising fasciitis?
Strep. pyogenes
How does necrotising fasciitis present?
- 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 there high risk of in necrotising fasciitis?
Compartment syndrome
How should necrotising fasciitis be managed?
Surgical review is mandatory
Imaging may help but could delay treatment
Antibiotics should be broad spectrum
- Flucloxacillin
- Gentamicin
- Clindamycin
What is pyomyositis?
- Purulent infection deep within striated muscle, often manifesting as an abscess
- Infection is often secondary to seeding into damaged muscle
Where does pyomyositis affect?
Common sites
- Thigh
- Calf
- Arms
- Gluteal region
- Chest wall
- Psoas muscle
Can affect multiple sites
How can pyomyositis present?
Can present with fever, pain and woody induration of affected muscle
If left untreated, what can pyomyositis lead to?
Septic shock and death
What are the predisposing factors fro pyomyositis?
- Diabetes mellitus
- HIV/immunocompromised
- Intravenous drug use
- Rheumatological diseases
- Malignancy
- Liver cirrhosis
What organisms can cause pyomyositis?
- Commonest:Staph aureus
- Gram positive and negatives
- TB
- Fungi
How is pyomyositis investigated?
CT or MRI
How is pyomyositis treated?
Treatment is drainage with antibiotic cover depending on Gram stain and culture results
What are bursae?
- Bursae are small sac-like cavities that contain fluid and are lined by synovial membrane
- Located subcutaneously between bony prominences or tendons
- Facilitate movement with reduced friction
How does septic bursitis commonly occur?
Infection spreads from adjacent skin infection
What predisposing factors are there for septic bursitis?
- Rheumatoid arthritis
- Alcoholism
- Diabetes mellitus
- Intravenous drug abuse
- Immunosuppression
- Renal insufficiency
How does septic bursitis present?
- Peribursal cellulitis, swelling and warmth are common
- Fever and pain on movement also seen
How is septic bursitis diagnosed?
Aspiration of the fluid
What organisms can cause septic bursitis?
-Commonest: staph aureus
Rarer organisms
- Gram negatives
- Mycobacteria
- Brucella
What is infectious tenosynovitis?
Infection of the synovial sheats that surround tendons
Where does infectious tenosynovitis commonly occur?
Flexor muscle-associated tendons and tendon sheaths of the hand most commonly involved
What event can incite infectious tenosynovitis?
Penetrating trauma
What organisms can cause infectious tenosynovitis?
Most common
-Staph aureus
Chronic infection
- Mycobacteria
- Fungi
Possibility of disseminated gonococcal infection
How does infectious tenosynovitis present?
- 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
How is infectious tenosynovitis treated?
- Empiric antibiotics
- Hand surgeon to review ASAP
What are toxin-mediated syndromes due to?
- Superantigens
- Group of pyrogenic exotoxins
How do toxin mediated syndrome occur?
- 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 organisms are implicated in toxin-mediated syndromes?
Staph aureus
- TSST1
- ETA and ETB
Strep pyogenes
-TSST1
What can cause toxic shock syndrome?
- Prolonged tampon use
- Staph aureus secreting TSST1 in small skin infections
What is the diagnostic criteria for staphylococcal TSS?
- 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 TSS associated with?
Almost always associated with presence of Streptococci in deep seated infections such as erysipelas or necrotising fasciitis
What is the treatment for streptococcal TSS?
Treatment necessitates urgent surgical debridement of the infected tissues
How does the mortality rate vary between strep and staph TSS?
- Strep 50%
- Staph 5%
How is TSS treated?
- Remove offending agent (ex tampon)
- Intravenous fluids
- Inotropes
- Antibiotics
- Intravenous immunoglobulins
What is staphylococcal scalded skin syndrome?
Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B
Who is commonly affected by staph scalded skin syndrome?
Usually occurs in children but rarely in adults as well
How does staph scalded skin syndrome present?
Characterised by widespread bullae and skin exfoliation
What is the treatment for staph scalded skin syndrome?
Treatment with intravenous fluids and antimicrobials
What is the mortality rate for staph scalded skin syndrome?
Mortality 3% in children but higher in adults who often are immunosuppressed
What is Panton-Valentine leucocidin toxin?
- It is a gamma haemolysin
- Can be transferred from one strain of Staph aureus to another, including MRSA
What can Panton-Valentine leucocidin toxin cause?
SSTI and haemorrhagic pneumonia
Who does Panton-Valentine leucocidin toxin tend to affect?
Tends to affect children and young adults
How does Panton-Valentine leucocidin toxin present?
Recurrent boils which are difficult to treat
How is Panton-Valentine leucocidin toxin treated?
Antibiotics which reduce toxin production
What are the risk factors for IV catheter associated infections?
- Continuous infusion >24 hours
- Cannula in situ >72 hours
- Cannula in lower limb
- Patients with neurological/neurosurgical problems
How do IV catheter associated infections tend to present?
- Normally starts as local SST inflammation progressing to cellulitis and even tissue necrosis
- Common to have an associated bacteraemia
- Commonly forms a biofilm which then spills into bloodstream
- Can seed into other places (ex endocarditis, osteomyelitis)
What organisms are commonly implicated in IV catheter associated infections?
Staph aureus (MSSA and MRSA)
How is a diagnosis of IV catheter associated infections made?
Diagnosis made clinically or by positive blood cultures
How are IV catheter associated infections managed?
- Treatment is to remove cannula
- Express any pus from the thrombophlebitis
- Antibiotics for 14 days
- Echocardiogram
How are IV 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
How are surgical wounds classified?
Class I
-Clean wounds
Class II
-Clean-contaminated wounds
Class III
-Contaminated wound
Class IV
-Infected wound
Class I surgical wound
Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
Class II surgical wound
Clean-contaminated wound (respiratory, alimentary, genital or infected urinary tracts entered but no unusual contamination)
Class III surgical wound
Contaminated wound(Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
Class IV surgical wound
Infected wound (existing clinical infection, infection present before the operation)
What organisms can cause surgical site infections?
- Staph aureus (incl MSSA and MRSA)
- 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 associated risk factors fro 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?
- 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)
How should surgical site infections be treated?
Antibiotics to target the likely organism
What SST infections require urgent attention?
- Necrotising fasciitis
- Pyomyositis
- Toxic shock syndrome
- PVL infections
- Venflon-associated infections
