Skin and Soft Tissue Infections Flashcards
what is most common childhood skin condition?
impetigo
where is it found of the body?
site of minor trauma; often on the face or other exposed areas
what does the infection look like?
Red patch with central fluid (vesicle)
Vesicles burst leaving golden crust
Clusters of lesions at affected site
(cf chicken pox)
what organisms mainly causes it?
Staphylococcus aureus
which other bacteria is less common but still causative?
Streptococcus pyogenes (Gp A streptococcus
which is harder to treat?
when infection is combined; both bacteria
how is it usually diagnosed?
visually, as it is so common in children
how is it treat?
Flucloxacillin (erythromycin if penicillin allergic)
A topical antibiotic cream
what happens if not responding to treatment?
Swab lesion for culture and sensitivity testing
may be MRSA
what is the more serious form of impetigo?
Bullous impetigo
what are the more serious symptoms?
Larger vesicles
Whole sheets of skin lifted off – resembles a burn
Leaves skin exposed to further infection
why are the symptoms more serious?
Staphylococcus aureus strains (phage typeII) secreting epidermolytic toxins
SSSS
what are abscesses?
localized collection of pus
what is a furuncle?
common boil
Localised swelling with central pus collection
where do they form on body?
hair follicle
what bacteria is usually the cause?
S. aureus
what is a Carbuncle?
Furuncle involving many follicles or glands
Multiple discharging heads
what is the content of abscesses?
Pus
Mostly fluid + neutrophils + causative organisms
where else can abscesses form?
Sites of trauma (puncture wounds)
how do abscesses form in deep tissues?
“seeded” by pyogenic organisms in bloodstream
“seeded” by trauma
what bacteria causes abscesses?
Mainly S. aureus but
Often polymicrobial, with obligate anaerobes
what causes Buttock abscesses?
Obligate anaerobes + other gut flora (eg enterobacteriaceae, streptococci)
what causes deep tissue abscesses?
Obligate anaerobes +/- streptococci +/- S. aureus
what is the first treatment of abscesses?
Incision and drainage
what has a secondary but crusail treatment role?
Antibiotics (penicillin/flucloxacillin + metronidazole)
why must abscesses be drained?
Antibiotics cannot penetrate the pus;
what diagnostic benefit does the drain have?
the pus can be collected and tested -
Microscopy (deep tissues only)
Culture (including anaerobic)
Sensitivity testing
what is Cellulitis?
Acute spreading infection under skin surface
how does the infection begin?
Access from minor trauma or existing infection (eg boil)
what does it look like?
Hot, red, swollen, painful. Fever.
what complications are associated with cellulitis?
Spread to deeper soft tissues eg fat and muscle
Septicaemia
what are the two main Causative organisms?
S. aureus
Streptococcus pyogenes (Gp A streptococcus + other ß haemolytic streps eg B, C and G)
what are the causative bacteria in buttock cellulitis?
Enterobacteriaceae and anaerobes
what can cause cellulitis rarely in the immunosupressed?
Pseudomonas
how is it diagnosed?
Clinical appearance
what lab tests are done?
Blood culture
Biopsy (rarely – only done if treatment failure)
ASO (anti-streptolysin O) titres if culture negative
what is used to treat?
Antistaphylococcal – flucloxacillin
+
Antistreptococcal – penicillin
why does the disease look as it does?
due to variety of toxins
what antibiotic should be used in severe disease?
use antibiotics that limit protein manufacture eg clindamycin
what is Erysipelas?
A specific type of cellulitis
how is the appearance different?
Generally head and neck only
Generally more superficial than cellulitis
Generally better defined edge
how does the causative organisms differ?
Almost always due to Group A Streptococci
Rarely Group G
what is Necrotising Fasciitis?
Spreading infection of deeper tissues
Destruction of connective tissue, fat, muscle
what are the associated side effects?
Extensive tissue destruction with loss of function
Risk of overwhelming infection, septicaemia and death
what are the causative organisms?
Often polymicrobial
Streptococci (Groups ABCGF)
Staphylococcus aureus
which Obligate anaerobic gram positive organisms can cause the infection?
Clostridial species
which Obligate anaerobic gram negative organisms can cause the infection?
Bacteroides species
it is Rarely monomicrobial; but which species could cause the infection alone?
Gp A streptococci, Clostridial species
how do the bacteria cause NF?
Pathogens encounter ischaemic tissue
Lytic toxins and toxins that promote spread
which toxins are produced?
(collagenases and hyaluronidases)
what predispositions you to NF?
Old age
Diabetes
Poor peripheral circulation – cardiovascular issues
Immunosuppression
how is NF diagnosed?
Microscopy of fluids and tissue samples
Aerobic and anaerobic culture of samples
Blood culture
how is NF treated?
Wide surgical excision of affected tissue
Antibiotics
what kind of antibiotics are used?
Cidal and Protein inhibitors
what are the Characteristics of puncture wounds?
Small or closed surface
Deep
what environmental contamination do they often contain?
Soil
Inorganic foreign body
what complications can be caused by these contaminates?
Cellulitis
Abscess formation
Osteomyelitis (location dependant)
what risk does soil contamination add in particular?
Tetanus (localised infection - systemic illness)
how are puncture wounds managed?
Clean
Remove damaged tissue and foreign body
which medicines are necessary?
Vaccinate against tetanus (if required)
Antibiotic cover
Depends on nature of injury
Often cover for anaerobic organisms
Uncomplicated puncture wound may not require any laboratory investigation. But why would Laboratory investigations ever be carried out?
depends on complications
Eg as for abscess, cellulitis
NB Tetanus is clinical diagnosis but:
Anaerobic culture of tissue sample may confirm
name particular types of puncture wounds?
object speared into body
animal bites
why do animal bites have more risk?
large bacterial inoculum from mouth commensals
what human pathogen bacteria is carried by dogs?
Capnocytophagia canimorsus
what human pathogen bacteria is carried by cats
Pasteurella multocida – only gram negative rod that is sensitive to penicillin
what can be carried from a human bite?
+ Streptococci, staphylococci and anaerobes
how are any pathogenic bacteria identified?
Culture (not microscopy) of swab of site
Microscopy and culture of any subsequent abscess
what are pressure sores?
Skin ulcerates due to prolonged pressure
what are the risk factors for developing pressure sores?
Faecal/urinary incontinence
Underlying fracture
Malnutrition
what bacteria are involved?
Colonisation of moist surface
S. aureus
Group G streptococci
Pseudomonas
All are potential pathogens
when are lab tests performed?
only for Deeper infection
Culture of swab from deep in lesion
or if antibiotics have no effect
what can cause infection of surgical wounds?
Patient’s endogenous flora from operation site
Normal flora of surgical team
what are the risk factors for infection of surgical wound
Length of operation
Subsequent haematoma
General health of patient
“Wound classification
what is meant by the classification of a ‘clean’ surgical wound?
Planned operation on uninfected tissue
‘clean / contaminated’
Planned procedure cutting mucous membranes
Infection risk dependent on normal flora at that site
‘contaminated’
Surgery on fresh trauma
Surgery on gut - Infection certain if antibiotic prophylaxis not given
‘infected’
Surgery on infected tissue
Surgery on old trauma site
what lab investigations are carried out?
Microscopy + culture: pus, infected tissues and infected fluids
Likely pathogens will vary with surgical site
Therefore culture methods will vary
But in most instances will include anaerobic culture
when is a blood culture done?
If systemically unwell patient
