Skin infections Flashcards
What are the two most common bacterial skin infections
- staph aureus
- B haemolytic streptococci (esp group a strep pyrogenes)
What is staph aureus
- Coagulase positive organism meaning it can produce the coagulase enzyme * all other staph cannot*
- The coagulase enzyme activates fibrinogen and leads to abscess formation
- Enzyme hyaluronidase will lyse fibrin clots and help spread infection
-Staph makes adhesions that attach to cell receptors or host CT and produce coagulase enzymes
Staph can produce toxins
- Toxic shock syndrome toxin 1
- Enterotoxin - food poisoning
There is a spectrum disease in staph aureus
- Colonisation
- Superficial skin infection
- Indirect staph skin syndromes - Staph scalded skin syndrome and TSS
What is staph aureus
- Coagulase positive organism meaning it can produce the coagulase enzyme * all other staph cannot*
- The coagulase enzyme activates fibrinogen and leads to abscess formation
- Enzyme hyaluronidase will lyse fibrin clots and help spread infection
-Staph makes adhesions that attach to cell receptors or host CT and produce coagulase enzymes
Staph can produce toxins
- Toxic shock syndrome toxin 1
- Enterotoxin - food poisoning
There is a spectrum disease in staph aureus
- Colonisation
- Superficial skin infection
- Indirect staph skin syndromes - Staph scalded skin syndrome and TSS
What is strep pyrogenes
- Capsulate bacteria disguises it from the immune system
- M-Proteins on bacteria help with adherence and phagocytosis resistance
- Produces toxins - streptomycin O (antibodies of this help diagnosis) and pyrogenic toxin (can cause necrotising fascitis)
- Produces enzymes - streptokinase -hyaluronidase -peptidases
Spectrum of disease in strep
- Colonisation (nasopharynx) -Superficial skin infection -Acute pharyngitis -Skin/ systemic infection
- Post strep syndromes- rheumatic fever and glomerulonephritis 1-3 weeks after
What is impetigo
-Pustules that break down and form gold crusts
-Usually in children aged 2-5
-Common in summer -Highly infectious - school exclusion while weeping
-Caused by staph aureus or staph pyrogenes
-Complications: Post strep glomerulonephritis
-Treatment: Encourage hygiene, don’t share towels
Topical in limited lesions- fusidic acid
Extensive lesions - flucloxcillin
What are some skin conditions commonly caused by staph aureus
- Folliculitis- hair follicle infection- superficial pus only in dermis
- Carbuncles- coalescence of many follicles- back of neck and usually diabetic
- Furuncles/ boils- extend into dermis, greater inflam - overlying pustule with hair emerging
Treatment with incision and drainage or if recurrent topical mu[irocin
What is Erysipelas
- Form of cellulitis affecting the most superficial skin layers
- More common in infants and elderly
- Abrupt onset with fever, chills , malaise
- Lesions raised above surrounding skin
- Clear line of demarcation
- Treatment= penicillin oral or iv
What is cellulitis
- Acute spreading pyodermic infection- inflam of dermis and subcutaneous tissue
- Preceeded by systemic flu/ malaise
- Lower limb most frequently affected
- MUST BE UNILATERAL TO BE CELLULITIS***
- Diffuse advancing edge
- Red hot, swollen, peau d’orange
- Lymphangitis
What is the management of cellulitis
- Identify risk factors -Obesity -Venous insufficiency -Lymphoedema -Trauma -Atheletes foot
- Diabetes
Can be caused by staph or strep so need to cover both
Mild- Oral Flucloxacillin
Moderate- IV flucloxacillin +/- benzylpenicillin
Severe- culture skin breaches/ do blood cultures and ask about being in fresh water - could be aeromonas hydrophia
If pen allergic give clindamycin
What are the most common organisms involved in bites
- Pasturella multiocida and anaerobes - dog bites
- Eikenella corrodes- human bites
- infection= most common complication
- High risk wounds= puncture wounds- deep innoculation, hand injuries, clenched fist injury
Management
TETANUS
-Prophylactic abx in high risk wounds, diabetic and immunosuppressed
-Give co-amoxiclav
How are surgical wound infections prevented/ managed
- Staph aureus= most common
- Depends on type of surgery - if contaminated or dirty then could be coliform strep or anaerobes
Prevention: Propylaxis to organisms encountered in procedure and infection control measures
Lab: Swab pus/ fluids or tissue biopsy for culture, blood culture if fever
Signs: Pain, swelling, erythema, purulent drainage> 5 days post op
If patient has a fever less than 5 days post op its not a wound infection causing it
Management: Incision and drainage of wound before abx
Clean/ clean contaminated surgery = high dose fluclox or clindamycin to cover staph aureus
Contaminated/ dirty= 2nd gen cephalosporin (Cefuroxime) and metronidazole OR co-amoxiclav to cover staph, strep, coliform and anaerobes
Describe the features and management of arterial ulcers
-Weak/ absent pulses -Low ankle brachial pressure index -Intermittent claudication -Hairless and shiny -ulcer well defined border
Management: Revascularise- bypass graft or angioplasty
Describe the features and management of a venous ulcer
-Superior to medial malleolus -Haemosiderin deposits -Oedema
Management: Compression therapy
What are diabetic and pressure ulcers
-Pressure ulcers- over sites of bony prominence
- Diabetic ulcers diabetic neuropathy
- plantar surface of foot -major predisposing factor to diabetic foot infection
What are signs of infection in an ulcer and what investigations would you do
- Delayed healing -poor quality granulation tissue -Fever -Pain/ red -Odour -Purulent exudate
- Cellulitis
investigations
- Chronic wound infection is a clinical diagnosis
- Swab wound after cleansing and remove slough before antiseptic/ abx given
- Tissue biopsies better than swabs
- only sample if there are clinical signs of infection
