Skin and Soft Tissue Infections Flashcards
What are the different areas where a skin or soft tissue infection can occur?
Epidermis - Impetigo Follicle - Folliculitis Dermis - Erysipelas Subcut Fat - Cellulitis (also affects deep dermis) Fascia - Necrotising Fasciitis Muscle
What host factors may predispose to developing a skin and soft tissue infection?
Diabetes
Immunosuppression
Renal Failure
Milroy’s Disease (congenital lymphadenopathy in legs)
Predisposing skin conditions - e.g. atopic dermatitis
What is impetigo?
A superficial skin infection common in young children that is highly infectious.
Golden crust, multiple vesicular lesions on erythematous base.
Where does impetigo tend to occur?
Exposed body parts; e.g. face, extremities and scalp
What organisms typically cause impetigo?
Usually staph aureus.
Sometimes strep pyogenes.
What are some predisposing factors for impetigo?
Skin abrasions Minor trauma Burns Poor Hygiene Insect Bites Eczema Chicken Pox Atopic Dermatitis
How do you treat impetigo?
Topical Abx
For large areas may add an oral abx like flucloxacillin
What organism commonly causes erysipelas (upper dermis infection)?
Strep pyogenes
Where does erysipelas most commonly occur?
Lower limbs and then the face
What factors increase the risk of erysipelas?
Milroy's Disease Venous Stasis Eczema DVTs Obesity Paraparesis Diabetes
What is the recurrence rate of erysipelas?
1/3 in 3 years
What are the common organisms in cellulitis?
In most patients: 50:50 staph aureus:strep pyogenes.
In diabetics and febrile neutropenics:
About 33:33:33 staph aureus:strep pyogenes:gram negative
What is the typical appearance of cellulitis?
Spreading red area of no distinct border, fever, lymphadenopathy and lymphangitis. Shiny oedematous skin.
What are some predisposing factors for cellulitis?
Diabetes
Tinea Pedis
Lymphoedema
How do you treat cellulitis?
Cover strep pyogenes and staph aureus - can do a combination but usually just give flucloxacillin, IV vancomycin or cotrimoxazole.
What are 3 different types of hair associated infection?
Folliculitis - superficial or deep, where only one follicle is involved
Furunculosis - infection all the way to subcut that normally only involves one follicle
Carbuncles - skin abscess where multiple follicles are involved in an area
What does folliculitis look like?
Circumscribed, pustular infection of hair follicle up to 5mm in diameter.
Head, back, buttocks and extremities.
What is the most common organism in folliculitis?
Staph aureus
What does furunculosis look like?
Boils - single hair follicle inflammatory nodule extending into dermis and subcut fat.
Moist, hairy, friction-prone areas
What common organism is found in furunculosis?
Staph aureus
What are risk factors for furunculosis?
Obesity Diabetes Atopic dermatitis CKD Chronic steroids
Where do we typically find carbuncles?
Neck, posterior trunk or thigh
What do carbuncles look like?
Multiseptated abscesses
How do you treat hair associated infections?
Folliculitis/Furunculosis - leave it or topical abx. If worse then maybe oral.
Carbuncles - admit, surgical drainage, possible IV abx
What are some predisposing factors for necrotising fasciitis?
Diabetes Surgery Trauma Peripheral vascular disease Skin popping
How many types of necrotising fasciitis are there?
4 - only look at 2 though
What is type 1 necrotising fasciitis?
Mixed aerobic and anaerobic infection
Common in diabetic foot and Fournier’s gangrene
What organisms can cause type 1 necrotising fasciitis?
Streptococci Staphylococci Enterococci Gram negative bacilli Clostridium
What is type 2 necrotising fasciitis?
Monomicrobial infection - normally associated with strep pyogenes
(Very painful leg)
What are the features of necrotising fasciitis?
Rapid onset
Extensive oedema and severe, unremitting pain
Haemorrhagic bullae, skin necrosis and crepitus
Systemic features, sepsis and death.
Anaesthesia at site of infection
What is mortality for necrotising fasciitis?
17-40%
What is treatment for necrotising fasciitis?
ABCDE - IV fluids
Surgical review
Broad spectrum abx (flucloxacillin, gentamicin, clindamycin)
What is pyomyositis?
Muscle abscess normally in the lower limbs - direct progression of cellulitis or seeding of another infection (IE)
What are common sites for pyomyositis?
Thigh Calf Glutes Psoas Arms Chest wall (Multiple sites in 15%)
What are predisposing factors for pyomyositis?
Diabetes HIV/Immunocompromised IV drug use Rheumatological diseases Malignancy Liver cirrhosis
What organisms cause pyomyositis?
Usually staph aureus
other gram positives/negatives, TB, fungi
How do you investigate pyomyositis?
CT/MRI
How do you treat pyomyositis?
Drainage and abx
What is septic bursitis?
Infection of the synovial sacs/bursae at joints close to bone, tendons and skin.
Infection often spreads from nearby skin.
Where are the most common areas for septic bursitis?
Patella and olecranon
What are some predisposing factors for septic bursitis?
Rheumatoid arthritis Alcoholism Diabetes IV Drug Use Immunosuppression Renal insufficiency
What is the most common cause of septic bursitis?
Staph aureus
rarer include gram negatives, mycobacteria and brucella in farmers and abroad
What is infectious tenosynovitis?
Infection of the synovial sheaths around tendons - commonly in the hands, fingers and toes
How does infectious tenosynovitis appear?
Red swollen semi-flexed finger that can’t move properly. Excrutiating pain on extension of finger.
What are the most common organism in infectious tenosynovitis?
Staph aureus and streptococci.
Chronic - mycobacteria and fungi
If not think gonorrhoea
What is the treatment for infectious tenosynovitis?
Empirical antibiotics and hand surgeon review.
What are toxin mediated syndromes?
Syndromes occur as a result of toxins produced by infecting bacteria.
Superantigens produced by gram positive bacteria are a common culprit. These pyrogenic toxins stimulate T-cells directly - activating up to 20% of them and causing a massive burst of cytokine release.
What are some consequences of the massive cytokine release in some toxin mediated syndromes?
Endothelial Leakage
Haemodynamic shock
Multi-organ failure
Death
What organisms can cause toxin mediated syndromes?
Mostly:
Staph aureus - causing TSST1, ETA and ETB
Strep pyogenes - causing TSST1
How do you diagnose staphylococcal TSS?
Fever
Hypotension
Diffuse Macular Rash
3 of (liver, blood, kidneys, GI, CNS, muscle) involved
Isolated staph aureus in mucosal/sterile sites
Production of TSST1 by isolate
Antibody development to toxin
Where does streptococcal TSS tend to come from?
Deep seated infections such as erysipelas and necrotising fasciitis
How do you treat strep TSS?
FAST - 50% mortality so need urgent surgical debridement of infected tissues
How do you treat TSS generally?
Remove offending agent IV fluid Inotropes Abx IV immunoglobulin
What toxin produces Staphylococcal Scalded Skin Syndrome?
Exfoliative toxin A or B from staph aureus
IV fluid and antimicrobials
What tends to occur as a result of Panton-Valentine Leucocydin toxin from staph aureus?
Recurrent boils and haemorrhagic pneumonia in children and young adults
What are risk factors for IV catheter associated infections?
Continuous infusion >24h
Cannula in situ >72h
Cannula in lower limb
Neurological/neurosurgical problems
What common organisms are found in IV catheter associated infections?
MSSA and MRSA
What are some complications of the resulting bacteraemia from seeding IV catheter associated infections?
Endocarditis and osteomyelitis
How would you treat an IV cannula associated infection?
Remove cannula
Express pus
Abx for 14 days
Echocardiogram to be safe
What are the 4 classes of surgical site infection?
I: Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
II: Clean-contaminated wound (above tracts entered but no unusual contamination)
III: Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
IV: Infected wound (existing clinical infection, infection present before the operation)
What can cause a surgical site infection?
Staph aureus (incl MSSA and MRSA) Coagulase negative Staphylococci Enterococcus Escherichia coli Pseudomonas aeruginosa Enterobacter Streptococci Fungi Anaerobes
