Soft tissue, bone and joint infections Flashcards
What is the aim of the skin and what are its 3 main layers?
physical barrier against microorganisms
3 layers:
1) epidermis: outer layer and waterproof
2) dermis: tough connective tissue, hair follicles and sweat glands
3) subcutaneous layer: fat and connective tissue
What are the non-specific defences of skin?
exfoliation: sloughing of the stratum corneum dislodges many adherent bacteria
dryness: bacterial counts much higher in moist areas
acidic: pH 5.5
low temperature
sweat glands: saltiness - inhibits bacteria
normal bacterial flora - complete for colonisation sites, compete for nutrients
What is the normal flora of the skin?
microorganisms are always present on the skin
- s epidermidis
- s aureus
- micrococci
- diphtheroids
some microorganisms are transient flora and are prevented from colonising due to:
- mechanical barrier
- sebum
- cleaning and washing
What type of organism is staphylococcus aureus?
gram +ve cocci and coagulase positive golden colonies - yellowy/cream colour 30-40% of population are colonised acquired resistance to beta-lactam antibiotics - methicillin causes haemolysis of red cells
What type of organism is streptococcus pyogenes?
group A streptococci
gram +ve cocci
beta haemolytic - get partial haemolysis of alpha chains
colonises the pharynx
What syndromes do you get within the epidermidis and dermis?
impetigo folliculitis furunculosis carbunculosis erysipelas \+ cellulitis
What syndromes do you get within the superficial fascia, subcutaneous fat, nerves, arteries, veins and deep fascia ?
necrotising fascitis
What syndrome do you get in the muscle?
myonecrosis
What conditions predispose to skin invasion?
excessive moisture - induces breakdown of the stratum corneum - occlusive dressings, obesity (infections seen in intertriginous folds)
minor abrasions
surgery
crush injuries - RTAs
burns - infections primary cause of death in burns patients
percutaneous e.g. intravenous catheters
bed sores- cutaneous lesions due to pressure lead to skin necrosis and secondary infections
conditions that compromise the blood supply- diabetes
What is impetigo?
superficial skin infection friable golden crusts over erythematous skin more common in children very contagious usually due to strep A
What is folliculitis?
infection of the hair follicles
common sites are groin and scalp
causative organism= s aureus
tx= flucloxacillin
What are some pyogenic skin infections?
furunculosis = deep inflammatory lesion progressing from a folliculitis
carbuncle = multiple fistulas = extend into the subcutaneous layer, multiple abscesses develop, separated by connective tissue
acute paronchia = skin infection arising from nail - remove nail and pus pores out
tx= oral flucloxacillin
What is cellulitis?
acute, spreading inflammation of the lower dermis and associated with subcutaneous layer of skin
diffuse inflammation without necrosis or localisation of pus
often seen as red halo around wound
skin is hot, red and painful
What is the causative agent of cellulitis commonly ?
s. aureus
less common- s pyogenes, c perfringens
How is cellulitis diagnosed?
most commonly affects lower extremities
acute, tender, erythematous and swollen area of skin - could be a DVT
fever and malaise
WCC and CRP usually raised
blood cultures only useful if pt is septic
What is the treatment for cellulitis?
rest and elevation
mark area of cellulitis
oral penicillin V and flucloxacillin
if severe may need IV abx
What is erysipelas?
infection involving the upper dermis and extends into the superficial cutaneous lymphatics
distinguished clinically by lesions raised above surrounding skin, clear line of demarcation of involved and not involved tissue
Group streptococci A most common cause
most common on legs or face
diagnosis: clinical appearance
treatment: penicillin
What is staphylococcal scalded skin syndrome?
seen in infants, young children and immunocompromised
clinical:
- starts with erythema, then fever, followed by large fluid filled bullae (large blister containing serous fluid), rupture and causes widespread exfoliation
toxins released into blood from localised S aureus infection - can die from this
Treatment: flucloxacillin
What do you worry that cellulitis might progress to?
necrotising fasciitis
What is necrotising fasciitis?
can be caused by one organism on its own (group A strept) or combination of bacteria
enter fascial plane following trauma, surgery or occult bacteraemia
inflammatory response - affects neurovascular bundles
thrombosis of vessels compromises blood supply and nerves to the skin
What are the 3 stages of symptoms in necrotising fasciitis?
1) early (<24 hours)
- presence of skin trauma but pain seems disproportionate to injury
- flu like symptoms and thirst
2) advanced symptoms
- swelling of painful area
- large dark blotches (violet)
- mottled flaky appearance at trauma site
3) critical symptoms
- severe fall in BP
- toxic shock from poisons released by bacteria
- unconsciousness
TX= IV abx and surgery
What is gas gangrene?
very rare - common cause of death in the past military conflicts - arising in devitalised wounds contaminated with soil
clostridium perfringens - most common cause - produces toxin which causes cell death
can occur in synergistic soft tissue infections e.g. wound contaminated with coliforms - use up oxygen making it amenable for anaerobes to grow
Tx= urgent surgery to remove dead tissue
Which patients is gas gangrene more common in ?
underlying blood vessel disease, diabetes or colon cancer
What are surgical site infections?
infections that affect the surgical wound or deeper tissues handled during the procedure resulting in local signs and clinical symptoms
up to 20% of all healthcare associated (nosocomial) infections - >5% of patients who undergo surgery develop an SSI
associated with morbidity, extended hospital stay and financial burden to patients and healthcare system
majority are preventable
