Skin and soft tissue infections Flashcards
Which bacteria cause impetigo?
- S aureus
- Strep pyogenes
Which layer of the skin is affected in impetigo?
Epidermis
Which bacteria cause folliculitis?
S aureus
Which bacteria cause Erysipelas?
Strep pyogenes
Which bacteria cause cellulitis?
- Strep pyogenes = Common
- S aureus = Uncommon
- H influenzae = Rare
- Other = Rare
Which layer of the skin is affected folliculitis?
Hair follicle = Dermis
Which layer of the skin is affected erysipelas?
Infection of the upper dermis
Which layer of the skin is affected cellulitis?
Deep dermis and subcutaneous fat
Which layer of the skin is affected necrotising fasciitis?
Subcutaneous fat and fascia, can invade muscle
Which bacteria cause necrotising fasciitis?
- Strep pyogenes
- Mixed bowel flora
What is a golden crust on the skin highly suggestive of?
Impetigo
How does impetigo present?
- Superficial skin infection
- Multiple vesicular lesions on an erythematous base
Who is most commonly affected with impetigo?
2-5 years of age
Where does impetigo often occur?
Exposed parts the body:
- Face
- Extremeties
- Scalp
Predisposing factors for impetigo?
> Skin abrasions > Minor trauma > Burns > Poor hygiene > Insect bites > Chickenpox > Eczema > Atopic dermatitis
How do you treat impetigo?
> Small areas can be treated with topical antibiotics alone
> Large areas need topical treatment and oral antibiotics (ex flucloxacillin)
How does someone present with erysipelas?
> Painful, red area (no central clearing)
Associated fever
Regional lymphadenopathy and lymphangitis
Typically has distinct elevated borders
Signs and symptoms of erysipelas?
> Painful, red area (no central clearing)
Associated fever
Regional lymphadenopathy and lymphangitis
Typically has distinct elevated borders
Most common cause of erysipelas?
Strep pyogenes
Which area of the body is most commonly affected by erysipelas?
> 70-80% of cases involved the lower limbs
> 5-20% affect the face
> Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
What is the reoccurrence rate of erysipelas?
High reoccurrence = 30% within 3 years
How does cellulitis present?
> Spreading erythematous area with no distinct borders
Fever is common
Regional lymphadenopathy and lymphangitis
Within diabetics which pathogens can cause cellulitis?
Gram negative bacteria
Within neutropenics which pathogens can cause cellulitis?
Gram negative bacteria
Which pathogens most commonly cause cellulitis?
Strep pyogenes
S aureus
What is a common complication of cellulitis?
Bacteraemia
Predisposing factors for cellulitis?
- Diabetes mellitus
- Tinea pedis
- Lymphoedema/ Lyphangitis/ Lymphadenitis
How do you treat erysipelas and cellulitis?
Anti-staphylococcal and Anti-streptococcal Abx:
> Penicillins:
- Benzylpenicillin, Penicillin V
- Co-amoxiclav
> Cephalosporins:
- 1st generation, cefradine
> Clidamycin
> tigecycline
Hair-associated infections?
- Folliculitis
- Furunculosis
- Carbuncles
What is folliculitis?
Circumscribed, pustular infection of a hair follicle
How does folliculitis presents?
> Small (Up to 5mm) small red papules
Central area of purulence that may rupture and drain
Typically on head, buttocks and extremities
Most common pathogen causing folliculitis?
S aureus
What are furuncles?
- Referred to as boils
- Single hair follicle-associated inflammatory nodule
Which layers of the skin are affected in furuncles?
Extending into dermis and subcutaneous tissue
Which areas are most commonly affected in furunculosis?
Usually affected moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)
What are the risk factors of furunculosis?
Risk factors include: > Obesity > Diabetes mellitus > Atopic dermatitis > Chronic kidney disease > Corticosteroid use
What is the most common organism that causes furunculosis?
S aureus
What is a carbuncle?
- Occurs when infection extends to involve multiple furuncles
- Multiseptated abscesses
Most common location of carbuncles?
Often located back of neck, posterior trunk or thigh
Risk associated with carbuncles?
Constitutional symptoms are common
How to treat hair-associated infections - folliculitis?
No treatment or topical antibiotics are required
How to treat hair-associated infections - furunculosis?
> No treatment or topical antibiotics are required
> Oral antibiotics might be necessary if not improving
What is necrotising fasciitis?
> An infectious disease emergency
> Necrotic
Which area of the body is most commonly affected in necrotising fasciitis?
Any site can be affected
Predisposing conditions in necrotising fasciitis?
Predisposing conditions include: > Diabetes mellitus > Surgery > Trauma > Peripheral vascular disease > Skin popping
Type I necrotising fasciitis?
Type I refers to a mixed aerobic and anaerobic infection (diabetic foot infection, Fournier’s gangrene)
Common organisms in type I necrotising fasciitis?
Typical organisms include: > Streptococci > Staphylococci > Enterococci > Gram negative bacilli > Clostridium
Common organisms in type II necrotising fasciitis?
Monomicrobial = Strep pyogenes
What is anaesthesia at the site of an infection highly suggestive of?
Necrotising fasciitis
Clinical features of necrotising fasciitis?
> Rapid onset
> Sequential development of erythema, extensive oedema and severe, unremitting pain
> Haemorrhagic bullae, skin necrosis and crepitus may develop
> Systemic features include fever, hypotension, tachycardia, delirium and multiorgan failure
> Anaesthesia at site of infection is highly
Imaging or not in necrotising fasciitis?
Imaging may help by could delay treatment
Which antibiotics are used in necrotising fasciitis?
- Flucloxacillin
- Gentamicin
- Clindamycin
If necrotising fasciitis is suggested what should be reviewed?
Surgical review
What is the overall mortality in necrotising fasciitis?
17-40%
What is pyomyositis?
Purulent infection deep within striated muscle, often manifesting as an abscess
What does pyomyositis often occur secondary to?
Often secondary to seeing into damaged muscle
Which areas of the body are commonly affected by pyomyositis?
Multiple sites involved in 15%: > Thigh > Calf > Arms > Gluteal region > Chest wall > Psoas muscle
How does someone present pyomyositis?
- Fever
- Pain
- Woody indication of affected muscle
What is the risk of untreated pyomyositis?
Untreated septic shock and death
Predisposing factors for pyomyositis?
Predisposing factors include: > Diabetes mellitus > HIV/immunocompromised > Intravenous drug use > Rheumatological diseases > Malignancy > Liver cirrhosis
What is the most common causes of pyomyositis?
S aureus
What are other organisms other than S aureus cause pyomyositis?
Gram positive/negatives, TB and fungi
Investigations in pyomyositis?
CT/MRI
Treatments in pyomyositis?
Treatment is drainage with antibiotic cover depending on Gram stain and culture results
What is septic bursitis?
> Bursae are small sac-like cavities that contain fluid and are lined by synovial membrane
> Located subcutaneously between bony prominences or tendons
What is the most common sites of septic bursitis?
Most common include patellar and olecranon
What does septic bursitis usually occur due to?
Often from adjacent skin infections
What are the predisposing factors of septic bursitis?
Other predisposing factors include: > Rheumatoid arthritis > Alcoholism > Diabetes mellitus > Intravenous drug abuse > Immunosuppression > Renal insufficiency
How does septic bursitis present?
> Peribursal cellulitis > swelling > warmth at the site > Fever > Pain on movement also seen
How is septic bursitis diagnosed?
Aspiration of the fluid
What is the most common organism that causes septic bursitis?
S aureus
What other organisms causes septic bursitis other than S aureus?
- Gram negatives
- Mycobacteria
- Brucella
What is infectious tenosynovitis?
Infection of the synovial sheats that surround tendons
What is the most common site of tenosynovitis?
Flexor muscle-associated tendons and tendon sheats of the hand most commonly involved
What is the most common cause of tenosynovitis?
Penetrating trauma
What is the most common organism of tenosynovitis?
- S aureus
- Streptococci
What is the most common organism in chronic tenosynovitis?
- Mycobacteria
- Fungi
What is a risk associated with tenosynovitis?
Disseminated gonococcal infection
How does infectious tenosynovitis present?
> Erythematous fusiform swelling of the finger
Semiflexed position
Tenderness over the length of the tendon sheet and pain with extension of finger
How to treat infectious tenosynovitis?
- Empiric Abx
- Hand surgeon to review ASAP
Diagnostic criteria for Staphylococcal 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
When does Streptococcal TSS most commonly occur?
In deep seated infections such as erysipelas or necrotising fasciitis
Which TSS Strep or Staph has higher mortality rate?
Streptococcus 50% vs 5%
How is streptococcal TSS treated?
> Urgent surgical debridement of infected tissues > Remove offending agent (ex tampon) > Intravenous fluids > Inotropes > Antibiotics > Intravenous immunoglobulins
What is Staphylococcal scalded skin syndrome?
> Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B
Widespread bullae and skin exfoliation
Who is most commonly affected by staphylococcal scalded skin syndrome?
Most common in children but rarely in adults
What is the treatment of staphylococcal scalded skin syndrome?
> IV fluids and antimicrobials
What is the mortality rate?
Around 3% in children but higher in adults who often are immunosuppressed
What is Panton-Valentine leucocidin toxin?
Gamma haemolysin
What is the big issue with Panton-Valentine leucocidin toxin and S aureus?
Can be transferred from one strain of Staph aureus to another, including MRSA
What can Panton-Valentine leucocidin toxin cause?
SSTI and haemorrhagic pneumonia
Who is commonly affected by Panton-Valentine leucocidin toxin?
Children and young adults
How does someone present with Panton-Valentine leucocidin toxin?
Recurrent boils which are difficult to treat
How do you treat Panton-Valentine leucocidin toxin?
Antibiotics that reduce toxin production
IV-catheter associated infections progression?
1) Local SST inflammation
2) Cellulitis
3) Tissue necrosis
4) Can cause bacteraemia
Risk factors for IV-catheter associated infections?
Risk factors for infections > Continuous infusion >24 hours > Cannula in situ >72 hours > Cannula in lower limb > Patients with neurological/neurosurgical problems
What is the most common organism that causes IV-catheter associated infections?
Staph aureus (MSSA and MRSA)
How does Risk factors for IV-catheter can infections?
> Commonly forms a biofilm which then spills int bloodstream
Can seed into other places (Endocarditis, osteomyelitis)
How are IV-catheter associated infections diagnosed?
Clinical or by positive blood cultures
How is IV-catheter associated infections treated?
1) Remove cannula
2) Express any pus from the thrombophlebitis
3) Abx for 14 days
4) Echo to rule out endocarditis
Prevention is key!
How can you prevent IV-catheter associated infections?
Prevention more important:
> 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
Classification of surgical site infections - Class I?
Class I: Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
Classification of surgical site infections - Class II?
Class II: Clean-contaminated wound (above tracts entered but no unusual contamination)
Classification of surgical site infections - Class III?
Class III: Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
Classification of surgical site infections - Class IV?
Class IV: Infected wound (existing clinical infection, infection present before the operation)
Organisms thar cause surgical site infections?
> Staph aureus (incl MSSA and MRSA) > Coagulase negative Staphylococci > Enterococcus > Escherichia coli > Pseudomonas aeruginosa > Enterobacter > Streptococci > Fungi > Anaerobes
Risk factors for surgical site infections - Patient associated?
Patient associated: > Diabetes > Smoking > Obesity > Malnutrition > Concurrent steroid use > Colonisation with Staph aureus
Risk factors for surgical site infections - procedural factors?
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
Diagnosis of surgical site infections?
> Importance of sending pus/infected tissue for cultures especially with clean wound infections
Avoid superficial swabs – aim for deep structures
Consider an unlikely pathogen as a cause if obtained from a sterile site (ex bone infection)
Which skin/tissue infections require urgent attention?
> Necrotising fasciitis > Pyomyositis > Toxic shock syndrome > PVL infecitons > Venflon-associated infections
