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Infection > skin and soft tissue infections > Flashcards

skin and soft tissue infections Flashcards

1
Q

what is impetigo?

A

Superficial skin infection
Multiple vesicular lesions on an erythematous base
Golden crust is highly suggestive of this diagnosis
Most commonly due to Staph aureus
Less commonly Strep pyogenes

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2
Q

who does impetigo most commonly affect?

A

Common in children 2-5 years of age
Highly infectious
Usually occurs on exposed parts of the body including face, extremities and scalp
Look for predisposing factors
Skin abrasions
Minor trauma
Burns
Poor hygiene
Insect bites
Chickenpox
Eczema
Atopic dermatitis

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3
Q

how is impetigo treated?

A

Small areas can be treated with topical antibiotics alone
Large areas need topical treatment and oral antibiotics (ex flucloxacillin)

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4
Q

what is erysipelas?

A

Infection of the upper dermis
Painful, red area (no central clearing)
Associated fever
Regional lymphadenopathy and lymphangitis
Typically has distinct elevated borders
Most commonly due to Strep pyogenes

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5
Q

who and where does erysipelas most commonly affect?

A

70-80% of cases involves the lower limbs
5-20% affect the face
Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
May involve intact skin
High recurrence rate (30% within 3 years)

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6
Q

what is cellulitis?

A

Diffuse skin infection involving deep dermis and subcutaneous fat
Presents as a spreading erythematous area with no distinct borders
Most likely organisms are Strep pyogenes and Staph aureus
Remember role of Gram negatives in diabetics and febrile neutropaenics
Fever is common
Regional lymphadenopathy and lymphangitis
Possible source of bacteraemia

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7
Q

what are predisposing factors for cellulitis?

A

Look for predisposing factors
Diabetes mellitus
Tinea pedis
Lymphoedema
Patients can have lymphangitis and/or lymphadenitis

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8
Q

Treatment of erysipelas and cellulitis?

A

A combination of anti-staphylococcal and anti-streptococcal antibiotics
In extensive disease, admission for intravenous antibiotics and rest

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9
Q

what are examples of hair associated infections?

A

Folliculitis
Furunculosis
Carbuncles

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10
Q

what is folliculitis?

A

Circumscribed, pustular infection of a hair follicle
Up to 5mm in diameter
Present as small red papules
Central area of purulence that may rupture and drain
Typically found on head, back, buttocks and extremities

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11
Q

what is the most common cause of folliculitis?

A

Most common organism is Staph aureus
Benign condition
Constitutional symptoms not often seen

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12
Q

what is Furunculosis?

A

Furuncles commonly referred as boils
Single hair follicle-associated inflammatory nodule
Extending into dermis and subcutaneous tissue
Usually affected moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)
May spontaneously drain purulent material

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13
Q

what is the most common cause of Furunculosis?

A

Staph aureus most common organism
Systemic symptoms uncommon
Risk factors include:
Obesity
Diabetes mellitus
Atopic dermatitis
Chronic kidney disease
Corticosteroid use

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14
Q

what is carbuncle?

A

Occurs when infection extends to involve multiple furuncles
Often located back of neck, posterior trunk or thigh
Multiseptated abscesses
Purulent material may be expressed from multiple sites
Constitutional symptoms common

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15
Q

what are the different treatments for hair-asscoiated infections?

A

With folliculitis, no treatment or topical antibiotics
With furunculosis, no treatment or topical antibiotics. If not improving oral antibiotics might be necessary
Carbuncles often require admission to hospital, surgery and intravenous antibiotics

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16
Q

what is necrotising fasciitis?

A

One of the infectious diseases emergencies
Any site may be affected
Predisposing conditions include
Diabetes mellitus
Surgery
Trauma
Peripheral vascular disease
Skin popping

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17
Q

what is type 1 nec fasc?

A

Type I refers to a mixed aerobic and anaerobic infection (diabetic foot infection, Fournier’s gangrene)
Typical organisms include
Streptococci
Staphylococci
Enterococci
Gram negative bacilli
Clostridium

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18
Q

what is type 2 nec fasc?

A

Type II is monomicrobial
Normally associated with Strep pyogenes

19
Q

what are symptoms and features of nec fasc?

A

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 suggestive of this disease

20
Q

how is nec fasc diagnosed and treated?

A

Surgical review is mandatory
Imaging may help but could delay treatment
Antibiotics should be broad spectrum
Flucloxacillin
Gentamicin
Clindamycin
Overall mortality ranges between 17-40%

21
Q

what is pyomyositis?

A

Purulent infection deep within striated muscle, often manifesting as an abscess
Infection is often secondary to seeding into damaged muscle
Multiple sites involved in 15%
Common sites include
Thigh
Calf
Arms
Gluteal region
Chest wall
Psoas muscle

22
Q

what is the presentation of pyomyositis?

A

Can present with fever, pain and woody induration of affected muscle
If untreated can lead to septic shock and death
Predisposing factors include
Diabetes mellitus
HIV/immunocompromised
Intravenous drug use
Rheumatological diseases
Malignancy
Liver cirrhosis

23
Q

what is a common cause of pyomyositis and its treatment?

A

Commonest cause is Staph aureus
Other organisms can be involved including Gram positive/negatives, TB and fungi
Investigation using CT/MRI
Treatment is drainage with antibiotic cover depending on Gram stain and culture results

24
Q

what is septic bursitis?

A

Bursae are small sac-like cavities that contain fluid and are lined by synovial membrane
Located subcutaneously between bony prominences or tendons
Facilitate movement with reduced friction
Most common include patellar and olecranon

25
Q

what are predisposing factors of septic bursitis?

A

Infection is often from adjacent skin infection
Other predisposing factors include
Rheumatoid arthritis
Alcoholism
Diabetes mellitus
Intravenous drug abuse
Immunosuppression
Renal insufficiency

26
Q

what are symptoms and signs odd septic bursitis?

A

Peribursal cellulitis, swelling and warmth are common
Fever and pain on movement also seen

27
Q

how are septic bursitisis diagnosed?

A

Diagnosis is based on aspiration of the fluid
Most common cause is Staph aureus
Rarer organisms include
Gram negatives
Mycobacteria
Brucella

28
Q

what is infectious tenosynovitis?

A

Infection of the synovial sheats that surround tendons
Flexor muscle-associated tendons and tendon sheats of the hand most commonly involved
Penetrating trauma most common inciting event
Most common cause Staph aureus and streptococci
Chronic infections due to mycobacteria, fungi
Possibility of disseminated gonococcal infection

29
Q

how does infectious tenosynovitis present?

A

Present with erythematous fusiform swelling of finger
Held in a semiflexed position
Tenderness over the length of the tendon sheat and pain with extension of finger are classical

30
Q

how is infectious tenosynovitis treated?

A

Empiric antibiotics
Hand surgeon to review ASAP

31
Q

what are toxin mediated syndromes?

A

Often due to superantigens
Group of pyrogenic exotoxins
Do not activate immune system via normal contact between APC and T cells
Superantigens bypass this and attach directly to the T cell receptors activating up to 20% of the total pool of T cells instead of the normal 1/10,000
Massive burst in cytokine release
Leads to endothelial leakage, haemodynamic shock, multi-organ failure and ?death

32
Q

what is the most common cause of toxin mediated syndrome?

A

Mostly due to some strains of Staphylococcus aureus and Streptococcus pyogenes
Staph aureus: TSST1
ETA and ETB
Strep pyogenes: TSST1

33
Q

what is diagnostic criteria for staphylococcal TSS?

A

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

34
Q

what is streptococca TSS?

A

Almost always associated with presence of Streptococci in deep seated infections such as erysipelas or necrotising fasciitis
Mortality rate is much higher than Staphylococcal (50% vs 5%)
Treatment necessitates urgent surgical debridement of the infected tissues

35
Q

how is TSS treated?

A

Remove offending agent (ex tampon)
Intravenous fluids
Inotropes
Antibiotics
Intravenous immunoglobulins

36
Q

Staphylococcal scalded skin syndrome

A

Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B
Characterised by widespread bullae and skin exfoliation
Usually occurs in children but rarely in adults as well
Treatment with intravenous fluids and antimicrobials
Mortality 3% in children but higher in adults who often are immunosuppressed

37
Q

Panton-Valentine leucocidin toxin

A

It is a gamma haemolysin
Can be transferred from one strain of Staph aureus to another, including MRSA
Can cause SSTI and haemorrhagic pneumonia
Tends to affect children and young adults
Patients present with recurrent boils which are difficult to treat
Treat with antibiotics that reduce toxin production

38
Q

Intravenous-catheter associated infections

A

Nosocomial infection
Normally starts as local SST inflammation progressing to cellulitis and even tissue necrosis
Common to have an associated bacteraemia
Risk factors for infections
Continuous infusion >24 hours
Cannula in situ >72 hours
Cannula in lower limb
Patients with neurological/neurosurgical problems

Most common organism is Staph aureus (MSSA and MRSA)
Commonly forms a biofilm which then spills into bloodstream
Can seed into other places (ex endocarditis, osteomyelitis)
Diagnosis made clinically or by positive blood cultures

39
Q

what is treatment for IV catheter asscoaiated infection?

A

Treatment is to remove cannula
Express any pus from the thrombophlebitis
Antibiotics for 14 days
Echocardiogram

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

40
Q

what are different classes of surgica; site infections?

A

Classification of surgical wounds
Class I: Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
Class II: Clean-contaminated wound (above tracts entered but no unusual contamination)
Class III: Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
Class IV: Infected wound (existing clinical infection, infection present before the operation)

41
Q

what are causes of surgical site infections?

A

Staph aureus (incl MSSA and MRSA)
Coagulase negative Staphylococci
Enterococcus
Escherichia coli
Pseudomonas aeruginosa
Enterobacter
Streptococci
Fungi
Anaerobes

42
Q

what are risk factors for surgical site infections?

A

Patient associated
Diabetes
Smoking
Obesity
Malnutrition
Concurrent steroid use
Colonisation with Staph aureus

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

43
Q

Diagnosis of surgical site infections

A

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)
Antibiotics to target likely organisms

Infection (14 decks)

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