Skin and Soft Tissue Infections Flashcards
name the layers of the skin
stratum corneum stratum lucidum stratum granulosum stratum spinosum stratum basale
what is the infection site in the epidermis?
impetigo
what is the infection site in the dermis and upper subcut fat?
folliculitis
erysipelas
what is the infection site in the lower dermis and upper sub cut fat?
cellulitis
what is the infection site in the lower subcut fat and muscle fascia
necrotising fascitis
organisms causing impetigo
s. aureus
strep pyogenes
organisms causing folliculitis
s. aureus
organisms causing erysipelas
strep pyogenes
organisms causing cellultitis
strep pyogenes (common)
s. aureus (uncommon)
h. influenzae (rare)
organisms causing necrotising fascitis?
strep pyogenes
mixed bowel flora
what is impetigo?
superficial skin infection
what does impetigo look like?
multiple vesicular lesions on an arythematous base
golden crust
causes of impetigo
most common s. aureus
less common strep pyogenes
what age is most affected by impetigo ?
2-5 yrs
how infectious is impetigo ?
highly
where does impetigo occur?
exposed parts of the body including face, extremities, scalp
predisposing factors for impetigo
skin abrasions minor trauma burns poor hygiene insect bites chickenpox eczema atopic dermatitis
treatment of impetigo
small area - topical antibiotics
large area - topical and oral antibiotics - flucloxacillin
what is erysipelas?
infection of the upper dermis
features of erysipelas?
painful, read area (no central clearning)
associated fever
regional lymphadenopathy and lymphangitis
typically has distinct elevated borders
most common cause of erysipelas
strep pyogenes
where does erysipelas occur?
70-80% - lower limbs
5-20% - face
areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, DM
what is the recurrence rate for erysipelas?
30% within 3 years
what is cellulitis?
diffuse skin infection involving deep dermis and subcutaneous fat
how does cellulitis present?
spreading erythematous area with no distinct borders
most common causes of cellulitis
strep pyogenes
staph aureus
features of cellulitis
fever
regional lymphadenopathy and lymphangitis
predisoposing factors for cellulitis
DM
tinea pedis
lymphoedema
treatment of erysipelas and cellulitis
combination of anti-staphylococcal and anti-streptococcal antibiotics
in extensive disease, admission for IV antibiotics
name the hair-associated infections
folliculitis
furunculosis
carbuncles
features of folliculitis
circumscribed, pustular infection of a hair follicle
up to 5mm in diameter
small red papules
central area of purulence that may rupture and drain
where is folliculitis typically found?
head
back
buttocks
extremities
most common cause of folliculitis
staph aureus
features of furunculosis
furuncles commonly referred tto as boils
single hair follicle associated inflammatory nodule
extending into dermis and SC tissue
may spontaneously drain purulent material
where does furunculosis commonly affect?
moist, hairy, friction prone areas of the body - face, axilla, neck, buttocks
most common organism causing furunculosis
staph aureus
systemic symptoms of furunculosis
uncommon
risk factors for furunculosis
obesity DM atopic dermatitis chronic kidney disease corticosteroid use
when does a carbuncle occur?
when infection extends to involve multiple furuncles
where are carbuncles often found?
back of neck
posterior trunk or thigh
features of carbuncle
multiseptated abscesses
purulent material may be expressed from multiple sites
systemic symptoms of carbuncle
common
treatment of folliculitis
no treatment or topical antibiotics
treatment of furunculosis
no treatment or topical antibiotics
if not improving oral antibiotics
treatment of carbuncle
often require admission to hospital, surgery and IV antibiotics
where can necrotising fasciitis occur?
anywhere
predisposing conditions for necrotising fasciitis
DM surgery trauma peripheral vascular disease skin popping
what is type 1 necrotising fasciitis?
mixed aerobic and anaerobic (diabetic foot infection, Fournier’s gangene)
type 1 necrotising fasciitis causative agents
streptococci staphylococci enterococci gram negative bacilli clostridium
what is type 2 necrotising fasciitis?
monomicrobial
type 2 necrotising fasciitis causative agents
strep pyogenes
features of necrotising fasciitis
rapid onset
sequential development of erythema, extensive oedema, and severe unremitting pain
haemorrhagic bullae, skin necrosis and crepitus
fever, hypotension, tachycardia, delirium and multiorgan failure
what feature is highly suggestive of necrotising fasciitis?
anaesthesia at site of infection
treatment of necrotising fasciitis
surgery
broad spectrum antibiotics - flucloxacillin, gentamicin, clindamycin
mortality from necrotising fasciitis
17-40%
what is pyomyositis?
purulent infection deep within striated muscle, often manifesting as an abscess
what is pyomyositis often secondary to?
seeding into damafed muscle
multipe sites of pyomyositis are involved in what %?
15%
common sites of pyomyositis
thigh calf arms gluteal region chest wall psoas muscle
features of pyomyositis
fever, pain, woody induration of affected muscle
if pyomyositis is untreatmed it can lead to?
septic shock and death
predisposing factors of pyomyositis
DM HIV immunicompromised IVDU rheumatological diseases malignancy liver cirrhosis
commonest cause of pyomyositis
staph aureus
other organisms causing pyomyositis
gram +ve/-ve
TB
fungi
investigation of pyomyositis
CT
MRI
treatment of pyomyositis
drainage with antbiotics
what are bursae?
small sac-like cavities that contain fluid and are lined by synovial membrane
where are bursae found?
subcutaneously between bony prominences or tendons
what do bursae do?
facilitated movement with reduced friction
most common sites of septic bursitis
patellar
olecranon
septic bursitis is infection often originating where?
adjacent skin
predisposing factors for septic bursitis
RA alcoholism DM IVDU immunospuression renal insufficiency
features of septic bursitis
peribursal cellullitis, swelling and warth
fever and pain on movement
diagnosis of septic bursitis
aspiration of the fluid
most common cause of septic bursitis
staph aureus
other causes of septic bursitis
gram -ve
mycobacteria
vrucella
what is infectious tenosynovitis?
infection of the synovial sheaths that surround tendons
where is infectious tenosynovitis most common?
flexor muscle associated tendons
tendons of hands
what is the most common initiating event of infectious tenosynovitis?
penetrating trauma
most common cause of infectious tenosynovitis
staph aureus
streptococci
what causes chronic infectious tenosynovitis?
mycobacterium
fungi
what may infectious tenosynovitis cause?
disseminated gonococcal infection
presentation of infectious tenosynovitis
erythematous fusiform swelling of finger
held in a semiflexed position
tenderness over the length of the tendon sheath and pain with extension
treatment of infectious tenosynovitis
empiric antibiotics
hand surgeon review
toxin mediated syndromes are often due to?
superantigens
mechanism of toxin mediated syndromes
• Group of pyrogenic exotoxins
• Do not activate immune system via normal
contact between APC and T cells
• Superantigens bypass this and attach directly to
the T cell receptors activating up to 20% of the
total pool of T cells instead of the normal
1/10,000
• Massive burst in cytokine release
• Leads to endothelial leakage, haemodynamic
shock, multi-organ failure and ?death
causes of toxin mediated syndromes
staph aureus - TSST1, ETA and ETB
strep pyogenes - TSST1
what can cause toxic shock syndrome?
tampons
small skin infections due to staph aureus
diagnostic criteria for staphlococcal TSS
• 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
streptococcal TSS is almost always associated with?
streptococci in deep seated infections such as erysipelas or necrotising fasciitis
mortality rate of strep and staph TSS
5% staph
50% strep
treatment of strep TSS
urgent surgical debridement
treatment of TSS
remove offending agent e.g. tampon IV fluids ionotropes antibiotics IV immunoglobulins
what is staphylococcal scalded skin syndrome?
infection due to a particular strain of staph aureus producing the exfoliative toxin A or B
what is staphylococcal scalded skin syndrome characterised by?
widespread bullae and skin exfoliation
who gets staphylococcal scalded skin syndrome?
children but rarely adults
treatment of staphylococcal scalded skin syndrome
IV fluids and antimicrobials
mortality rate of staphylococcal scalded skin syndrome
3% in children
higher in adults who are often immunosuppressed
what is panton-valentine leucocidin toxin?
gamma haemolysin
panton-valentine leucocidin toxin can be transferred from?
one strain of staph aureus to another including MRSA
what can panton-valentine leucocidin toxin cause?
SSTI
haemorrhagic pneumonia
who gets panton-valentine leucocidin toxin?
children and young adults
presentation of panton-valentine leucocidin toxin
recurrent boils which are difficult to treat
treatment of panton-valentine leucocidin toxin
antibiotics that reduce toxin production
IV catheter associated infections are what kind of infections?
nosocomial
what do IV catheter associated infections normally start as and progress to
start as locall SST inflammation progressing to cellulitis and even tissue necrosis
risk factors for IV catheter associated infections
continuous infusion > 24 hrs
cannula in situ > 72 hrs
cannula in LL
patients with neurological/neurosurgical problems
most common organism IV catheter associated infections
Staph aureus
what does staph aureus in IV catheter associated infections form?
biofilm which spills into blood stream
where can IV catheter associated infections end up?
endcocarditis
osteomyelitis
diagnosis of IV catheter associated infections
clinically or by positive blood cultures
treatment of IV catheter associated infections
remove cannula
express pus from the thrombophlebitis
antibiotics for 14 days
echocardiogram
prevention of 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
describe the classification of surgical wounds: class 1
clean wound
resp, alimentary, genital or infected urinary systems not entered
describe the classification of surgical wounds: class 2
clean-contaminated wound
resp, alimentary, genital or infected urinary systems entered but no unusual contamination
describe the classification of surgical wounds: class 3
contaminated wound
open, fresh accidental wounds or gross spillage from the GIT
describe the classification of surgical wounds: class 4
infected wound
existing clinical infection, infection present before the operation
causes of SSI
- Staph aureus (incl MSSA and MRSA)
- Coagulase negative Staphylococci
- Enterococcus
- Escherichia coli
- Pseudomonas aeruginosa
- Enterobacter
- Streptococci
- Fungi
- Anaerobes
risk factors for SSI: patient associated
– Diabetes – Smoking – Obesity – Malnutrition – Concurrent steroid use – Colonisation with Staph aureus
risk factors for SSI: 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
