Skin and Soft Tissue Infections Flashcards
What is impetigo?
Superficial skin infection
Describe the character of impetigo skin lesions?
- Multiple vesicular lesions on erythematous base
- Golden crus highly suggestive of this diagnosis
What is impetigo most and least commonly due to?
Most commonly due to staph aureus, least commonly due to strep pyogenes
What infection is this?
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Impetigo
Who does impetigo commonly infect?
Commonly affects children, is highly infectious
What are some risk factors for impetigo?
- Skin abrasions
- Minor trauma
- Burns
- Poor hygiene
- Insect bites
- Chickenpox
- Eczema
- Atopic dermatitis
What is the treatment of impetigo?
- Small area
- Topical antibiotics alone
- Large area
- Topical treatment and oral antibiotics (such as flucloxacillin)
What is erysipelas?
Infection of the upper dermis
What is the presentation of erysipelas?
- Painful, red area (no central clearing)
- Associated fever
- Regional lymphadenopathy and lymphangitis
- Typically has distinct elevated borders
What is erysipelas most commonly due to?
Most commonly due to strep pyogenes
What infection is this?
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Erysipelas
Where does erysipelas mostly affect?
Mostly affects lower limbs, then face
What is cellulitis?
Diffuse skin infection involving deep dermis and subcutaneous fat
What is the presentation of cellulitis?
- Spreading erythematous area with no distinct borders
- Fever is common
- Possible source of bacteraemia
What are the most likely organisms that cause cellulitis?
Most likely organisms are strep pyogenes and staph aureus
What infection is this?
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Cellulitis
What are risk factors for cellulitis?
- Diabetes
- Tinea pedis
- Lymphoedema
What is the treatment for erysipelas?
- Combination of anti-staph and anti-strep antibiotics
- In extensive disease, admission for IV antibiotics
What is the treatment of cellulitis?
- Combination of anti-staph and anti-strep antibiotics
- In extensive disease, admission for IV antibiotics
What are examples of hair associated infections?
- Folliculitis
- Furunculosis
- Carbuncles
What is folliculitis?
Circumscribed, pustular infection of a hair follicle
Describe the character of folluculitis lesions?
- Small red papules
- Up to 5mm in diameter
- Central area of purulence that may rupture and drain
- Typically found on head, back, bum and extremities
What infection is this?
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Folliculitis
What is the most common organism causing folliculitis?
Staph aureus
What is the treatment for folliculitis?
- No treatment or topical antibiotics
What is furunculosis?
Single hair follicle associated inflammatory nodule extending into dermis and subcutaneous tissue
What is furunculosis commonly refered to as?
Boils
Describe the character of furunculosis lesions?
- Usually affects moist, hairy, friction prone areas of body
What infection is this?
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Furunculosis
What organism most commonly causes furunculosis?
Staph aureus
What are risk factors for furunculosis?
- Obesity
- Diabetes
- Atopic dermatitis
- CKD
- Corticosteroid use
Are systemic symptoms with furunculosis common?
- Systemic symptoms uncommon
What is the treatment of furunculosis?
- No treatment or topical antibiotics
- If not improving oral antibiotics
What is carbuncle?
Occurs when infection extends to involve multiple furuncles
Describe the character of carbuncle lesions?
- Often located back of neck, posterior trunk or thigh
- Multiseptated abscesses
Are systemic symptoms common with carbuncle?
- Systemic symptoms common
What infection is this?
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Carbuncle
What is the treatment for carbuncle?
- Surgery
- IV antibiotics
Necrotising fasculitis is a…
Infectious disease emergency
What are risk factors for necrotising fasculitis?
- Diabetes
- Surgery
- Trauma
- Peripheral vascular disease
- Skin popping
What are the different types of necrotising fasculitis?
- Type 1
- Refers to mixed aerobic and anaerobic infection
- Such as diabetic foot infection, or Fournier’s gangrene
- Organisms includes
- Streptococci
- Staphylococci
- Enterococci
- Gram negative bacilli
- Clostridium
- Type 2
- Is monomicrobial
- Normally associated with strep pyogenes
What organisms cause type 1 necrotising fascultiis?
- Streptococci
- Staphylococci
- Enterococci
- Gram negative bacilli
- Clostridium
What organism is type 2 necrotising fasculitis typically associated with?
Strep pyogenes
What is the presentation of necrotising fasculitis?
- Rapid onset
- Sequential development of erythema, extensive oedema and severe paion
- Haemorrhagic bullae, skin necrosis and crepitus may develop
- Systemic features
- Fever
- Hypotension
- Tachycardia
- Delerium
- Multiorgan failure
What investigations are done for necrotising fasculitis?
- Surgical review is mandatory
- Imaging may help but could delay treatment
What is the treatment for necrotising fasculitis?
- Antibiotics should be broad spectrum
- Flucloxacillin
- Gentamicin
- Clindamycin
What is pyomyositis?
Purulent infection deep within striated muscle
What is the presentation of pyomyositis?
- Often manifests as abscess
- Common sites
- Thigh
- Calf
- Arms
- Gluteal region
- Chest wall
- Psoas muscle
- Fever and pain
- If untreated can lead to septic shock and death
What are risk factors for pyomyositis?
- Diabetes mellitus
- HIV/immunocompromised
- Intravenous drug use
- Rheumatological diseases
- Malignancy
- Liver cirrhosis
What organism is the most common cause of pyomyositis?
Staph aureus
What investigations should be doen for pyomyositis?
- CT/MRI
What is the treatment for pyomyositis?
- Drain with antibiotic cover depending on gram stain and culture results
What are bursae?
Small sac-like cavities that contain fluid and are lined by synovial membrane
Where are bursae located?
Located subcutaneously or between bony prominences or tendons
What are risk factors for septic bursitis?
- Infection often from adjacent skin infection
- Rheumatoid arthritis
- Alcoholism
- Diabetes mellitus
- Intravenous drug abuse
- Immunosuppression
- Renal insufficiency
What infection is this?
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Septic bursitis
What is the presentation of septic bursitis?
- Peribursal cellulitis, welling and warmth
- Fever and pain on movement
Septic bursitis is diagnosed by what?
Diagnosis based on aspiration of fluid
What organism is the most common cause of septic bursitis?
Most common cause is staph aureus, rarer organisms include:
- Gram negatives
- Mycobacteria
- Brucella
What is infectious tenosynovitis?
Infection of the synovial sheets that surround tendons
Where does infectious tenosynovitis most commonly affect?
Most commonly affects flexor muscle and associated tendons of the hand
What is the most common cause of infectious tenosynovitis?
Most common cause is staph aureus and streptococci, chronic infections occur due to mycobacteria and fungi
What is the presentation of infectious tenosynovitis?
- Erythematous fusiform swelling of finger
- Hand held in semiflexed position
- Tenderness over the length of the tendon sheet with pain on extension of finger
What is the treatment of infectious tenosynovitis?
- Empiric antibiotics
- Hand surgeon to review
What are toxin mediated syndromes often due to?
Often due to super antigens such as group of pyrogenic exotoxins
Describe the pathophysiology of toxin mediated syndromes?
- Do not activate immune system via normal contact between APC and T cells
- Superantigens bypass this and attach directly to T cell receptors activating them
- Massive bursts of cytokines released
- Leads to endothelial leakage, haemodynamic shock, multiorgan failure and maybe death
What are toxin mediated syndromes mostly due to?
- Some strains of staph aureus
- TSST1
- ETA and ETB
- Some strains of streptococcus pyogenes
- TSST1
What toxins can staph aureus release that causes toxin mediated syndromes?
- TSST1
- ETA and ETB
What toxin can strep pyogenes release that causes toxin mediated syndromes?
TSST1
What is the diagnostic criteria for staph TSS?
- Fever
- Hypotension
- Diffuse macular rash
- Three of following organs involved
- Liver, blood, renal, GI, CNS, muscular
- Isolation of staph aureus from mucosal or normally sterile sites
- Production of TSST1 by isolate
- Development of antibody to toxin
What does TSS stand for?
Toxin shock syndrome
Does strap or strep TSS have a higher mortality rate?
Strep (50% vs 5%)
What is the treatment for toxin shock syndrome?
- Remove offending agent (ex tampon)
- Intravenous fluids
- Inotropes
- Antibiotics
- Intravenous immunoglobulins
What often causes toxin shock syndrome?
Tampons
What is staph scaled skin syndrome?
Infection due to particular strain of staph aureus producing the exfoliative toxin A or B
What is the presentation of staph scaled skin syndrome?
- Widespread bullae and skin exfoliation
- Usually occurs in children but rarely in adults
hat is the treatment of staph scaled skin syndrome?
- IV fluids and antimicrobials
What infection is this?
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Staph scaled skin syndrome
What is the Penton-Valentine Leucocodin (PVL) toxin?
Is a gamma haemolysin
Can be transferred from one strain of staph to another including MRSA
Describe the character os lesions due to PVL toxin?
- Recurrent boils
What is the treatment of PVL toxin?
- Antibiotics to reduce toxin production
What can PVL toxin cause?
Can cause SSTI (skin and soft tissue infection) and haemorrhagic pneumonia
What does SSTI stand for?
Skin and soft tissue infection
Where do IV catheter associated infections originate?
Nosocomial (originates in hospital) infection
Desribe the pathogenesis of IV catheter associated infections?
- Starts as local SST inflammation
- Progresses to cellulitis and even tissue necrosis
What are 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
What organism most commonly causes IV catheter associated infections?
Most common organism is staph aureus (MSSA and MRSA), which commonly forms a biofilm which then spills into bloodstream
How are IV catheter associated infections diagnosed?
- Made clinically or by positive blood cultures
What is the treatment for IV catheter associated infections?
- Remove cannula
- Express any pus from the thrombophlebitis
- Antibiotics for 14 days
- Echocardiogram
What are ways to prevent IV catheter associated infections?
- 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 different classification of surgical wounds?
- Class 1
- Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
- Class 2
- Clean-contaminated wound (above tracts entered but no unusual contamination)
- Class 3
- Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
- Class 4
- Infected wound (existing clinical infection, infection present before the operation)
What are some examples of surgical site infection causative organisms?
- Staph aureus (incl MSSA and MRSA)
- Coagulase negative Staphylococci
- Enterococcus
- Escherichia coli
- Pseudomonas aeruginosa
- Enterobacter
- Streptococci
- Fungi
- Anaerobes
What are some risk factors for surgical site infections?
- Patient associated
- Diabetes
- Smoking
- Obesity
- Malnutrition
- Concurrent steroid use
- Colonisation with Staph aureus
- Procedural factors
- 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/infection tissue for culture
- Aim for deep structures with swabs not superficial
What is the treatment for surgical site infections?
- Antibiotics to target likely organisms