Skin and Soft Tissue Flashcards
What causes impetigo?
Most commonly S. Aureus, less commonly S. pyogenes
Describe impetigo
Superficial skin infection
Multiple vesicular lesions on erythematous base
Golden crust highly suggestive
Common 2-5yo, highly infectious
What are predisposing factors to impetigo?
- skin abrasions
- minor trauma
- burns
- poor hygiene
- insect bites
- chicken pox
- eczema
- atopic dermatitis
Describe treatment of impetigo
Small areas treated with topical abs alone
Large areas both topical and oral abs (flucloxacillin)
Describe erysipelas
Infection of upper dermis, painful, red area (no central clearing)
Associated fever
Regional lymphadenopathy and lymphangitis
Typically distinct elevated borders
What causes erysipelas?
most commonly S pyogenes
Where does erysipelas tend to occur?
Areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
Describe cellulitis
Diffuse skin infection involving deep dermis and subcutaneous fat
Presents as a spreading erythematous area with no distinct borders
Fever is common, regional lymphadenopathy and lymphangitis
Possible source of bacteraemia
What causes cellulitis?
Most likely organisms are S.Pyogenes and S.Aureus
What are predisposing factors to cellulitis?
Diabetes mellitus
Tinea pedis
Lymphoedema
What is the treatment of erysipelas and cellulitis?
A combination of anti-staphylococcal and anti-streptococcal abs
In extensive disease, admission for IV Abs and rest
What are some hair associated infections?
Folliculitis
Furunculosis
Carbuncles
What is a folliculitis?
erythema and pustule in a single follicle
up to 5mm in diameter
present as small red papules
typically found on head, back, buttocks and extremities
What is a furuncle?
red, tender nodule surrounding a follicle with one draining point
Commonly “boils”, extending into dermis and subcutaenous tissue
Usually affects moist, hairy, friction-prone areas
Systemic symptoms uncommon
What are carbuncles?
Deep follicular abscesses of several follicles with several drainage points
Often back of neck, posterior trunk or thigh
Multiseptated abscesses, purulated material may be expressed from multiple sites
Constitutional symptoms common
What causes folliculitis and furunculosis?
Staph aureus most common
What are risk factors for furunculosis?
Obesity, diabetes mellitus, chronic kidney disease, corticosteroid use
How do you treat hair-associated infections?
Folliculitis; no treatment or topical abs
Furunculosis; no treatment or topical abs. If not improving oral abs may be req
Carbuncles; often require admission, surgery and IV Abs
Describe necrotising fasciitis
An infectious disease emergency
Any site may be affected
Rapid onset
What are predisposing conditions for necrotising fasciitis?
Diabetes mellitus Surgery Trauma Peripheral vascualr disease Skin popping
What is type I necrotising fasciitis?
Refers to mixed aerobic and anaerobic infection
Typical organisms
- strep
- staph
- enterococci
- gram -ve bacilli
- clostridium
What is type II necrotising fasciitis?
Monomicrobial
Normally associated with S Pyogenes
How does necrotising fasciitis develop?
Erythema
Extensive oedema
Severe, unremitting pain
Haemorrhagic bullae, skin necrosis and crepitus may develop
Systemic features include; fever, hypotension, tachycardia, delirium, multiorgan failure
Anaesthesia at site of infection is highly suggestive of this disease
How is necrotising fasciitis treated?
Surgical review mandatory
Abs should be broad spectrum
- flucloxacillin
- gentamicin
- clindamycin
overall mortality between 17-40%
Describe pyomyositis
Purulent infection deep within striated muscle, often manifesting as abscess
infection often secondary to seeding into damaged muscle
What are common sites of pyomyositis?
- thigh
- calf
- arms
- gluteal region
- chest wall
- psoas muscle
How does pyomyositis present?
Fever, pain, woody induration of affected muscle
if untreated can lead to septic shock and death
what are predisposing factors to pyomyositis?
- diabetes mellitus
- HIV/immunocompromised
- IV drug use
- rheumatological diseases
- malignancy
- Liver cirrhosis
What causes pyomyositis?
Most commonly S. Aureus
other organisms can be involved including gram positives and negatives, TB and fungi
How do you investigate pyomyositis?
CT/MRI
What is the treatment of pyomyositis?
Drainage with antibiotics cover depending on gram stain and culture results
Describe septic bursitis
Infection most common from adjacent skin infection
Peribursal cellulitis, swelling and warmth are common
Fever and pain on movement
What is a bursa?
Small sac-like cavities containing fluid, located subcutaneously between bony prominences and tendons
Facilitate movement with reduced friction
Most common are patellar and olecranon
What are predisposing factors to septic bursitis?
- rheumatoid arthritis
- alcoholism
- diabetes mellitus
- IV drug abuse
- immunosuppression
- renal insufficiency
How is septic bursitits diagnosed?
Based on aspiration of the fluid
What causes septic bursitis?
Most common cause is S.Aureus
Rarer organisms include
- gram negatives
- mycobacteria
- brucella
Describe infectious tenosynovitis
Infection of synovial sheets that surround tendons
Penetrating trauma most common inciting event
Present with erythemtous fusiform swelling or finger, held in a semi-flexed position
Tender over length of tendon sheet and pain on extension
What causes infectious tenosynovitis?
Most common cause S.aureus and streptococci
Chronic infections due to mycobacteria, fungi
Possibility of disseminated gonococcal infection
Management of infectious tenosynovitis
- Empirical Abs
- Hand surgeon review ASAP
Describe toxin-mediated syndromes
Often due to super-antigens
Group of pyrogenic exotoxins
Do not activate immune system via normal contact between APC and T cells
Superantigens bypass this and attach directly to T cell receptors
Massive cytokine release
Endothelial leakage, haemodynamic shock, multi-organ failure, ?death
What causes toxin mediated syndromes?
Most commonly due to some strains of S.Aureus (TSST, ETA and ETB) and S.Pyogenes (TSST1)
What are diagnostic criteria for staph toxic shock syndrome?
Fever, hypotension, diffuse macular rash
three of the following organs
- liver, blood, renal, GI, CNS, muscular
Isolation of S.Aureus from mucosal or normally sterile sites
Development of antibody to toxin
Describe strep TSS
Almost always associated w/ strep presence in deep seated infections
Mortality rate much higher than in staph
Treatment = urgent surgical debridement of infected tissues
Describe treatment of TSS
Remove offending agent (ex tampon)
IV fluids
Inotropes
ABs
IV Igs
Describe staph scalded skin syndrome
Infection due to particular strain of S.Aureus producing exfoliative toxin A or B
Widespread bullae and skin exfoliation
Usually children
How do you treat Staph scalded skin syndrome?
IV fluids and antimicrobials
Describe panton-valentine leucocidin toxin
Gamma-haemolysin
Can be transferred from one S.Aureus strain to another (incl MRSA)
Can cause SSTI and haemorrhagic pneumonia
Present with recurrent boils, difficult to treat
How do you treat panton-valentine leucocidin toxin?
ABs that reduce toxin production
What are risk factors for IV catheter associated infections?
- continuous infusion >24hours
- cannula in situ >72hours
- cannula in lower limb
- patients with neurological/neurosurgical problems
How do IV catheter associated infections progress?
Normally starts as local SST inflammation progressing to cellulitis and even tissue necrosis
What causes IV catheter associated infections?
Most commonly S.Aureus (MSSA and MRSA)
Commonly forms biofilm which then spills into bloodstream
What is the treatment for IV catheter associated infections?
Remove cannula
Express any pus from thrombophlebitis
ABs for 14 days
Echocardiogram
PREVENTION MORE IMPORTANT;
don’t leave unused cannula, don’t insert unless using, change cannulae every 72hours, use aseptic technique when inserting
How are surgical wounds classified?
Class I - IV
What is a class I surgical wound?
Clean wound (resp, alimentary, genital or infected urinary systems not entered)
What is a class II surgical wound?
Clean-contaminated wound (resp, alimentary, genital or urinary tracts entered but no usual contamination)
What is a class III surgical wound?
Contaminated wound (open, fresh accidental wounds or gross spillage from GIT)
What is a class IV surgical wound?
Infected wound (existing clinical infection, infection present prior to operation)
What causes surgical site infections?
- S.Aureus
- coagulase negative Staph
- enterococcus
- E. Col
- pseudomonas aeruginosa
- enterobacter
- strep
- fungi
- anaerobes
What are patient associated risk factors for surgical site infections?
- diabetes
- smoking
- obesity
- malnutrition
- concurrent steroid use
- colonisation w/S.Aureus
What are procedural risk factors for surgical site infections?
- shaving of site
- improper peroperative skin prep
- improper antimicrobial prophylaxis
- break in sterile technique
- inadequate theatre ventilation
- perioperative hypoxia
How do you diagnose surgical site infections?
Send pus/infected tissue for cultures
Avoid superficial swabs; aim for deep structures
Consider an unlikely pathogen as a cause if obtained from a sterile site
Treatment of surgical site infections
Antibiotics to target likely organisms
