Skin and Soft Tissue Infections Flashcards
Most common organisms associated with skin and soft tissue infections? (2)
Staph aureus
Group A Streptococcus pyogenes
How does the coagulase enzyme produced by staph aureus act as a virulence factor?
Activates fibrinogen and is important in abscess formation
What syndrome does the toxin TSST-1 (toxic syndrome one-1) cause?
Toxic shock syndrome, systemic illness
How does the enzyme hyaluronidase act as a virulence factor?
Produced by staph aureus, lyses fibrin clots and assists in spread of infection
What organism causes scalded skin syndrome in babies?
Staph aureus
Well recognised carriage sites of staph aureus on the human body?
Anterior nares, skin of axilla and groin
How does a capsule act as a virulence factor for streptococcus pyogenes?
Immunological disguise
How does M protein act as virulence factor for streptococcus pyogenes?
Adherence, helps to resist phagocytosis
Which organism produces these toxins: Streptolysin O, Streptolysin S, pyrogenic toxin
Streptococcus pyogenes
Pyrogenic toxin responsible for some of the severe manifestations of necrotising fasciitis
How can you detect the presence of a previous or recent streptococcal infection?
Antibodies to streptolysin O
Where does streptococcus pyogenes normally colonise on the human body?
Nasopharynx
Name the two post streptococcal syndromes
Rheumatic fever
Glomerulonephritis
Arise a few weeks after an infection. Immunologically related.
Aetiology of impetigo?
Staph aureus
Strep pyogenes
Complication of impetigo
Post-streptococcal glomerulonephritis
Treatment for impetigo
Topical fusidic acid/mupirocin
Flucloxacillin
Exclude from school
Strict hygiene, don’t share towels
What is folliculitis?
Superficial infection of hair follicle, caused by staph aureus, pus only in epidermis
What are carbuncles?
Infection of multiple adjacent follicles usually on the back of the neck
Inflammatory mass with multiple sinuses
Patient is often diabetic
What are furuncles?
Commonly known as boils
Infection of hair follicle that extends into dermis with more inflammation that folliculitis
Inflammatory nodule is present often with a hair seen emerging from this
Treatment of larger furuncles/carbuncles?
Incision and drainage
Abx not usually needed
Treatment of recurrent furunculosis
Occurs in staph aureus carriers (carried in their anterior nares) therefore topical MUPIROCIN on the anterior nares
Recurrence also occurs in diabetics
What is erysipela?
Form of cellulitis affecting most superficial layers of skin
More common in infants and elderly
Symptoms of erysipelas
Superficial cellulitis affecting infants and elderly
Abrupt onset with fever, chills, malaise
Raised lesions on red hot area of skin which is well demarcated
What area of the body does erysipelas affect?
Lower legs 70-80%
Face 5-10%
Tx of erysipelas
Penicillin, oral or IV
Which skin layer is affected by cellulitis?
Dermis and subcutaneous fat
Symptoms of cellulitis
Preceded by fever/flu like symptoms
Skin red, hot, swollen (peau d’orange)
Advancing diffuse edge
Risk factors for cellulitis (6)
Obesity Venous insufficiency Lymphoedema Trauma Athletes foot Diabetes
Which organisms cause cellulitis?
MOSTLY will be staph aureus
Or strep pyogenes
BUT in cases of trauma it may be a more unusual cause (eg dog bite with Pasteurella and mixed anaerobes)
Treatment of mild cellulitis?
Oral flucloxacillin (covers both staph and strep)
Treatment of moderate to severe cellulitis?
IV flucloxacillin +/- benzylpenicillin
Treatment of cellulitis with penicillin allergy?
Clindamycin
Investigations for cellulitis?
Skin swab of any breaches
Blood cultures if severe
CLINICAL DIAGNOSIS
Which animals have pasteurella mulocida in their bites?
Cats and dogs
Which animals have anaerobes in their bites?
cats, dogs and humans
Which animals have eikenella corrodens in their bites?
Humans
Management of bites?
Prophylactic abx for high risk wounds and high risk patietns
CO-AMOXICLAV covers all relevent pathogens
Don’t forget tetanus
Most common organism in surgical infection?
Staph aureus
Surgical infection: organisms in contaminated or dirty wounds?
Coliform streps and anaerobes
General management of surgical wound infections
Open and drain
Abx not always necessary
Abx for surgical wound with staph aureus
Flucloxacillin OR clindamycin
Abx for dirty surgical wound infection (eg staph, strep, coliforms, anaerobes)
Second generation cephalosporin such as:
CEFUROXIME + METRONIDAZOLE
OR
Co-amoxiclav
4 types of chronic wound
Arterial
Venous
Pressure sores
Diabetic ulcers
Symptoms of arterial ulcer
Weak or absent pulses Reduced ABPI Intermittent claudication Skin hairless and shiny Ulcer with well defined border
Tx for arterial ulcer?
Revascularise with bypass grafting or angioplasty
Symptoms of venous ulcer
Superior to medial malleolus
Haemosiderin deposits
Lipodermatosclerosis
Oedema
Management for venous ulcer
Compression therapy
Where do pressure ulcers arise?
Over sites of bony prominence
Where do diabetic ulcers occur?
Mostly on plantar surface of foot
How many diabetic patients have diabetic ulcers at any time?
4-20%
True/false: diabetic ulcers are leading cause of traumatic amputations
FALSE, leading cause of NON-traumatic amputations. 40-60%
Investigations for chronic wound infection
Swab wound bed after cleansing and removal of slough but BEFORE antiseptics and antibiotics
Tissue biopsies better than swabs
ONLY SAMPLE WHEN ?infection
Positive swab result is not a directive to treat
Debriding options for chronic wounds (3)
Surgical
Chemical
Larvae
Local antiseptics for chronic wounds (2)
Cadexomer iodine
Silver products
General management of chronic wounds
Debridement, local antiseptics, and use of complex dressings to keep wound bed moist
Reserve antibiotics for systemic infection
What is single most important pathogen in diabetic foot infection?
Staph aureus
May be polymicrobial in deep or severe infection
Describe a mild diabetic foot infection
<2cm radius of cellulitis around wound
Describe a moderate diabetic foot infection
> 2cm cellulitis radius
Deep infection
Describe a severe diabetic foot infection
Deep infection
Systemic sepsis
What is necrotising fasciitis?
A RARE, life-threatening, rapidly progressive subcutanous infection which tracks along fascial planes
How does necrotising fasciitis spread?
Tracks along the fascial planes
3 types of necrotising fasciitis?
Polymicrobial NF
Group A strep NF (flesh eating)
Clostridial myonecrosis (gas gangrene)
When does polymicrobial necrotising fasciitis occur?
After trauma or surgery
An example is Fournier’s gangrene
Involves staph, strep, anaerobes, coliforms, and aerobic gram negatives
What is another name for Group A streptococcal NF?
Flesh eating NF
Can occur in fit and healthy people
Result of minor trauma
What is another name for Clostridial myonecrosis?
Gas gangrene, caused by Clostridium perfringens
Symptoms and signs of necrotising fasciitis
HAVE HIGH SUSPICION INDEX
Overlying cellulitis
Pain OUT OF KEEPING with signs
Skin necrosis
Crepitus
Confusion
Hypotension
How to confirm necrotising fasciitis diagnossi?
Surgical exploration
Treatment of necrotising fasciitis
Surgical emergency
Aggressive debridement
ICU
Antibiotics: High doses of benzylpenicillin, clindamycin, ciprofloxacin
What 3 abx are used for necrotising fiasciitis?
BCC
Benzylpenicillin
Clindamycin
Ciprofloxacin
Causes of ringworm (3)
Trichophyton
Microsporum
Epidermophyton
How is ringworm/tinea spread?
Zoonotic, human to human (shared towels, hairbrushes)
How is ringworm diagnosed?
Clinical appearance
Direct microscopic exam of scales in potassium hydroxide
Culture of scrapings
FLUORESCENCE UNDER WOOD’S LIGHT FOR TINEA CAPITIS
Tx for tinea/ringworm?
Topical imidazoles 2-4 wks
Oral terbinafine for resistant cases
Which antibiotics increase risk of MRSA?
Quinolones
Cephalosporins
Treatment for mild MRSA infection?
Tetracyclines
Treatment for severe MRSA infection?
Glycopeptides:
-IV VACNOMYCIN/ TEICOPLANIN
What is CA-MRSA?
Community associated MRSA
Affects young, healthy adults and children
No associated risk factors
What organism produces the toxin Panton-Valentin Leukocid (PVL)
CA-MRSA
What is the infection rate of mammal bites?
30-50%
