skin and soft tissue infections Flashcards
what is impetigo
epidermis - superficial skin infection
highly infectious
e.g. S. aureus (more common), Strep pyogenes
what is folliculitis
circumscribed, pustular infection of a hair follicle
e.g. S. aureus
what is erysipelas
infection of the dermis
e.g. Strep pyogenes
what is cellulitis
diffuse infection of the deep dermis and subcutaneous fat
e.g. Strep pyogenes (common), S. aures (uncommon)
H. influenzae and other (rare)
role of gram -ve bacteria in diabetics and febrile neuropaths
what is necrotising fasciitis
infection of the subcutaneous fat and underlying fascia
e.g. Strep pypgenes or mixed bowel flora
things to consider in skin and soft tissue infections
site - possible complications w/ specific sites e.g. abdo, face
organism
host
environment
host factors to consider in skin and soft tissue infections i.e. predisposing factors
diabetes leading to neuropathy and vasculopathy
immunosuppression
renal failure
Milroy’s disease
predisposing skin conditions e.g. atopic dermatitis
environmental factors to consider in skin and soft tissue infections
drug resistant strains (MRSA)
drus interactions
drug allergies
appearance of impetigo
multiple vesicular lesions on an erythematous base
golden crust is highly suggestive of this diagnosis
what is this skin infection
impetigo
at what age is impetigo most common
where does impetigo usually occur
exposed parts of the body including face, extermities and scalp
predisposing factors to impetigo
skin abrasions
minor trauma
burns
poor hygiene
inset bites
chicken pox
eczema
atopic dermatitis
treatment of impetigo
small areas - topical abx
large areas - topical treatment + oral abx (flucloxacillin)
appearance of erysipelas
painful red area
no central clearing
associated
what is this skin infection
erysipelas
where does erysipelas tend to occur
70-80% - lower limbs
5-20% - face
tends to occur in areas of pre-existing lypmphoedema, venous stasis, obesity, paraparesis, DM
may involve intact skin
recurrence rate of erysipelas
high
30% within 3yrs
appearance and presentation of cellulitis
spreading erythematous area w/ no distinct borders
fever is common
regional lymphadenopathy and lymphangitis
possible source of bacteraemia
what skin infection is this
cellulitis
predisposing factors to cellulitis
DM
tinea pedis (athlete’s foot - common cause in otherwise healthy pts)
lymphoedema
what condition is this
lymphangitis
treatment of erysipelas and cellulitis
combination of anti-staphylococcal and anti-streptococcal abx
extensive disease - admission for IV abx and rest
hair associated infections (3)
folliculitis
furunculosis
carbuncles
what infection is this
appearance of folliculitis
up to 5mm diameter
present as small red papules
central area of purulence that may rupture and drain
typically found on head, back, buttocks and extremities
constitutional symptoms not often seen
furunculosis
aka boils
single hair follicle-associated inflamamtory nodule
extending into dermis and subcutaneous tissue
usally affected moist, hairy, friction-brone areas of the body (face, axilla, neck buttocks)
systemic symptoms uncommon
may spontaneously drain purulent material
what infection is this
furunculosis
common causative organism for furunculosis
risk factors for furunuculosis
obesity
DM
atopic dermatitis
chronic kidney disease
corticosteroid use
carbuncle
infection extends to involve mutliple furunucles
often located in back of neck, posterior trunk or thigh
multiseptated abscesses
purulent material may be expressed from multiple sites
consititutional symptoms common
what skin infection is this
carbuncle
treatment of hair associated infections
folliculitis - no treatment or topical abx
furunuculosis - no treatment or topical abx, oral abx may be necessary if not improving
carbuncles - hospital admission, surgery and IV abx
necrotising fasciitis
infectious disease emergency
any site may be affected
predisposing conditions to necrotising fasciitis
DM
surgery
trauma
peripheral vascular disease
skin popping
type I necrotising fasciitis
mixed aerobic and anaerobic infection - diabetic foot infection, Fournier’s gangrene
typical organisms: streptococci, staphylococci, enterococci, gram -ve bacilli, clostridium
what skin infection is this
Fuornier’s gangrene
type II necrotising fasciitis
monomicrobial
normally associated w/ strep pyogenes
what skin infection is this
type II necrotising fasciitis
presentation of necrotising fasciitis
rapid onset
sequential development of erythema, extensive oedma and severe unremitting pain
haemorrhagic bulla, skin necrosis, crepitus may develop
systemic features: fever, hypotension, tachycardia, delirium and multi-organ failure
anaesthesia at site of infection is highly suggestive of necrotising fasciitis
management of necrotising fasciitis
mandatory surgical review
imaging may help but coule delay treatment
broad spectrum abx - flucoloxacillin, gentamicin, clindamycin
17-40% overall mortality
what is pymomyositis
purulent infection deep within striated muscle, often manifesting as an abscess
infection is often 2y to seeding into damage muscle
sites of pyomyositis
multiple sites involved in 15%
common sites: thigh, calf, arms, gluteal region, chest wall, psoas muscle
presentation of pyomyositis
fever
pain
woody induration of affected muscle
untreated can lead to septic shock and death
predisposing factors to pyomyositis
DM
HIV/immunocompromised
IV drug use
rhematological diseases
malignancy
liver cirrhosis
causative organisms for pyomyositis
S. aureus is commonest
gram+ve/-ve, TB, fungi
management of pyomyositis
investiagtion w/ CT/MRI
treatment: drainage and abx cover depending on gram stain and culture results
what does this MRI show
pyomyositis of R thigh muscles
septic bursitis
small sac-like cavities that contain fluid and are lined by synovial membrane
located subcutaneously between bony prominences or tendons
facilitate movement w/ reduced friction
most common include patellar and olecranon
predisposing factors for septic bursitis
infection is often from adjacent skin infection
rheumatoid arthritis
alcoholism
DM
IVDU
immunosuppression
renal insufficiency
what infection is shown here
pre-patellar septic bursitis
presentation of septic bursitis
peribursal cellulitis, swelling and warmth
fever and pain on movement
causative organisms of septic bursitis
diagnosis based on aspiration of fluid
most common cause - S. aureus
rarer - gram -ve, mycobacteria, brucella
what is infectious tenosynovitis
infections of the synovial sheats that surround tendons
flexor muscle-associated tendons and tendon sheeth of the hand most commonly involved
causes of infectious tenosynovitis
S. aureus and streptococci
penetrating trauma is most common inciting event
chronic infections due to mycobacteria, fungi
possibility of disseminated gonococcal infection
presentation of infectious tenosynovitis
erythematous fusiform swelling of finger
held in semi-flexed position
tenderness over the length of the tendon sheath and pain w/ extension of finger
treatment of infectious tenosynovitis
empirial abx
hand surgeon to review
what causes toxin mediated syndromes
often due to superantigens
group of pyrogenic exotoxins
associated w/ use of high absorbency tampons
can also be due to small skin infections (Staph aureus secreting TSST1)
immune response in toxin mediated syndromes
don’t activate immune system via normal contact between APC and T cells
superantigens bypass this and attach directly to the T cells receptors acivating up to 20% of the total pool of T cells (instead of normal 1/10 000)
massive burst in cytokine release
leads to endothelial leakage, haemodynamic shock, mutliorgan failure and death
causative organsisms of toxin-mediated syndromes
some strains of Staph aureus (TSST1, ETA and ETB) and strep pyogenes (TSST1)
diagnostic criteria for staphylococcal TSS
fever
hypotension
diffuse macular rash
3 of the following involved: liver, blood, renal, GI, 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 condition is shown here
toxic shock syndrome
streptococcal TSS
almost always associated w/ presence of streptococci in deep seated infections e.g. erysipelas or necrotising fasciitis
mortality rate is much higher than staphylococcal - 50% vs 5%
treatment requires urgent surgical debridement of infected tissues
treatment of TSS
remove offending agent e.g. tampon
IV fluids
inotropes
abx
IV immunoglobulins
staphylococcal scalded skin syndrome
infection due to a particular strain of S. aureus producing the exfoliative toxin A or b
presentation of staphylococcal scalded skin syndrome
widespread bullae and skin exfoliation
usually occurs in children, rarely in adults
treatment of staphylococcal scalded skin syndrome
IV fluids and antimicrobials
mortality 3% in children, higher in adults who often are immunosuppressed
what condition is this
staphylococcal scalded skin syndrome
what is panton-valentine leucocidin toxin
gamma haemolysin
can be transferred from one strain of S. aureus to another, including MRSA
can cause SSTI and haemorrhagic pneumonia
presentation of panton-valentine leucocidin toxin and treatment
tends to affect children and young adults
pts present w/ recurrent boils that are difficult to treat
treat w/ abx that reduce toxin production
intravenous catheter associated infections
nosocomial infection
normally starts as local SST infection progressing to cellulitis and even tissue necrosis
common to have associated bacteraemia
risk factors for intravenous catheter associated infections
continuous infusion >24hrs
cannula in situ >72hrs
cannula in lower limb
pts w/ neurological/neurosurgical problems
causative organisms of intravenous catheter associated infections and how it spreads
staph aureas (MSSA and MRSA)
commonly forms a biofilm which then spills into bloodstream
can seed into other places (endocarditis, osteomyelitis)
diagnosis made clinically or by +ve blood cultures
what infection is shown here
intravenous catheter associated infections
treatment of intravenous catheter associated infections
remove cannula
express any pus from the thrombophlebitis
abx for 14 days
echocardiogram
prevention is more important
prevention of intravenous catheter associated infections
don’t leave unused cannula
don’t insert cannula unless it will be used
change cannula every 72hrs
monitor for thrombophlebitis
use aseptic technique when inserting cannula
class I surgical site infection
clean wound
resp, alimentary, genital or infected urinary systems not entered
class II surgical site infection
clean-contaminated wound
resp/GI/genital/infected urinary tract entered but no unusual contamination
class III surgical site infection
contaminated wound
open, fresh accidental wounds or gross spillage from GI tract
class IV surgical site infection
infected wound
existing clinical infection
infection present before the operation
what class fo surgical site infection is this
class I
what class of surgical site infection is this
class IV
wet gangrene
diabetic foot amputation
causes of surgical site infections
staph aureus (incl MSSA and MRSA) - most common
coagulase -ve staphylococci
enterococcus
E. coli
psudomonas aeruginosa
enterobacter
streptococci
fungi
anaerobes
patient associated risk factors for surgical site infections
diabetes
smoking
obesity
malnutrition
concurrent steroid use
colonisation w/ staph aureus
procedural risk factors for surgical site infections
shaving of site the night prior to procedure
improper preoperative skin preparation
improper antimicrobial prophylaxis
break in sterile technique
inadequate theatre ventilation
perioperative hypoxia
diagnosis of surgical site infections
send pus/infected tissue for cultures esp w/ clean wound infections
avoid superficial swabs - aim for deep structures
consider an unlikely pathogen as a cause if obtained from a sterile site e.g. bone infection
abx to target likely organisms
