Skin and Soft Tissue Infections Flashcards
What is the most superficial skin infection?
Impetigo
How does impetigo present?
Multiple vesicular lesions on an erythematous base
Golden crust highly suggestive
Most commonly on extremities, face and scalp
Most common in children aged 2-5
What are the common causative organisms of impetigo?
Staph aureus (most common) Strep pyogenes
What are the predisposing factors for impetigo?
Skin abrasions Minor trauma Burns Poor hygiene Insect bites Chickenpox Eczema Atopic dermatitis
How is impetigo treated?
Topical antibiotics alone if only small area affected
Oral antibiotics plus topical antibiotics if large are
What is erysipelas an infection of?
The upper dermis
How does erysipelas present?
Painful, bubbly, raised, red area with no central clearing. Rash usually has distinct elevated borders
Associated fever
Regional lymphadenopathy
Lymphangitis
Most cases affect lower limb but can affect face too
What is the most common causative organism for erysipelas?
Strep pyogenes
When is erysipelas most common?
In areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis or diabetes
What is infected in cellulitis?
Deep dermis
Subcutaneous fat
How does cellulitis present?
A spreading erythematous area with no distinct borders
Fever
Regional lymphadenopathy
Lymphangitis
What are the most common causative organisms of cellulitis?
Strep pyogenes
Staph aureus
What are the predisposing factors for cellulitis?
Diabetes mellitus
Tinea pedis
Lymphoedema
How are erysipelas and cellulitis treated?
Combination of anti-staphylococcal and anti-streptococcal antibiotics
What are the common hair-associated infections?
Folliculitis
Furunculosis
Carbuncles
What is folliculitis?
Circumscribed, pustular infection of a hair follicle
How does folliculitis present?
Small red papules that are up to 5mm in diameter
Central area of purulence that may rupture and drain
Lesions are typically found on the head, back, buttocks and extremities
What is the most common causative organism of folliculitis?
Staph aureus
How is folliculitis treated?
Treatment rarely required
Topical antibiotics
What is furunculosis?
Involves furuncles
A single hair follicle-associated inflammatory nodule that extends into the dermis and subcutaneous tissue
Most common on face, axilla, neck and buttocks
What is the most common causative organism of furunculosis?
Staph aureus
What are the risk factors for furunculosis?
Obesity Diabetes mellitus Atopic dermatitis Chronic kidney disease Corticosteroid use
How is furunculosis treated?
Treatment rarely required
Topical antibiotics
Oral antibiotics if condition won’t improve
What are the features of carbuncles?
Occur when infection extends to involve multiple furuncles
Often on back of neck, posterior trunk and thigh
Present as multiseptated abscesses and purulent material can be expressed from multiple sites
Systemic symptoms common
Treatment involves admission, surgery and IV antibiotics
What are the predisposing factors for necrotising fasciitis?
Diabetes mellitus Surgery Trauma Peripheral vascular disease Skin popping (IV drug users run out of venous sites and inject intra-dermally)
What is the difference between type I and type II necrotising fasciitis?
Type I- mixed aerobic and anaerobic infection
Type II- monomicrobial, more common than type I
What are the causative organisms of type I and II necrotising fasciitis?
Type I: -Streptococci -Staphylococci -Enterococci -Gram negative bacilli -Clostridium Type II usually strep pyogenes
How does necrotising fasciitis present?
Lesion similar to cellulitis but pain is severe
Rapid onset
Sequential development of erythema, extensive oedema and severe pain
Haemorrhagic bullae, skin necrosis and crepitus may also develop
Systemic features can include fever, hypotension, tachycardia, delirium and multiorgan failure
Anaesthesia at sight of infection highly suggestive of NF
How should necrotising fasciitis be managed?
Surgical review mandatory
Imaging can be helpful but shouldn’t delay treatment
Broad spectrum antibiotics should be used (gentamicin, flucloxacilin, clindamycin)
What is pyomyositis?
A purulent infection deep with striated muscle, often manifesting as an abscess
What are the common sites of pyomyositis?
Thigh Calf Arms Gluteal region Chest wall Psoas muscle
How does pyomyositis present?
Fever
Pain
Woody induration of affected muscle (cardinal sign)
If untreated the infection can lead to septic shock and death
What are the predisposing factors for pyomyositis?
Diabetes mellitus HIV/immunocompromised Intravenous drug use Rheumatological diseases Malignancy Liver cirrhosis
What are the common causative organisms of pyomyositis?
Staph aureus (most common)
TB
Fungi
How is pyomyositis managed?
CT and MRI can be helpful
Drainage plus antibiotics
What is septic bursitis?
Infection of the bursae
What are the predisposing factors for septic bursitis?
Adjacent skin infection Rheumatoid arthritis Alcoholism Diabetes mellitus Intravenous drug abuse Immunosuppression Renal insufficiency
What are the clinical features of septic bursitis?
Peri-bursal cellulitis Swelling Warmth Fever Pain on movement
How is septic bursitis diagnosed?
Aspiration of fluid (FNA not often done in practice due to risk of infecting an uninfected bursa)
What are the common causative organisms of septic bursitis?
Staph aureus (most common)
Gram-negative bacteria
Mycobacteria
Brucella
What is infectious tenosynovitis?
Infection of the synovial sheets surrounding tendons
Flexor muscle-associated tendons and tendon sheets of the hand are the most commonly affected
What are the causes of infectious tenosynovitis?
Penetrating trauma
Most common causative organisms are staph aureus and streptococci
How does infectious tenosynovitis present?
Erythematous fusiform swelling of a finger that is held in a semi-flexed position
Tenderness over the length of the tendon sheet
Pain when extending finger
How is infectious tenosynovitis managed?
Empirical antibiotics
Reviewal from hand surgeon
Describe the process of toxin-mediated syndromes?
Often due to superantigens, resulting in a massive burst in cytokine release. This leads to endothelial leakage, haemodynamic shock, multi organ failure and death
What are the most common causative organisms of toxin-mediated syndromes?
Staph aureus
Strep pyogenes
What are the diagnostic criteria for staphylococcal 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 are the characteristics of streptococcal toxic shock syndrome?
Streptococcal toxic shock syndrome is almost always associated with the presence of streptococci in deep seated infections such as erysipelas or necrotising fasciitis. Mortality rate is much higher than in staphylococcal TSS. Treatment requires urgent surgical debridement of the infected tissues.
How is toxic shock syndrome treated?
Remove offending agent (ex tampon) Intravenous fluids Inotropes Antibiotics Intravenous immunoglobulins
What is staphylococcal scalded skin syndrome?
An infection due to a particular strain of staphylococcal aureus producing the exfoliative toxin A or B
How is staphylococcal scalded skin syndrome characterised?
Widespread bullae and skin exfoliation. It usually occurs in children but can also occur in adults
How is staphylococcal scalded skin syndrome treated?
IV fluids and antimicrobials
What are the characteristics of Panton-Valentine leucocidin toxin?
Can be transferred from one staph aureus strain to another
Can cause SSTI and haemorrhagic pneumonia
Most commonly affects children and young adults
Patients present with recurrent, difficult to treat boils
Treatment with antibiotics
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
What is the most common infective organism in IV-catheter associated infections?
Staph aureus
How are IV-catheter associated infections diagnosed?
Clinically
Positive blood cultures
How are IV-catheter associated infections treated?
Removal of cannula
Removing pus from the thrombophlebitis
Antibiotics for 14 days
ECG to check for spread to heart wall
What are the preventative measures for 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
How are surgical site wounds classified?
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 risk factors for surgical site infections?
Diabetes Smoking Obesity Malnutrition Concurrent steroid use Colonisation with Staph aureus 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?
Sending pus or infected tissue for cultures
Avoid superficial swabs