Skin and Soft Tissue Infections Flashcards

1
Q

What are the different areas where a skin or soft tissue infection can occur?

A
Epidermis - Impetigo
Follicle - Folliculitis
Dermis - Erysipelas
Subcut Fat - Cellulitis (also affects deep dermis)
Fascia - Necrotising Fasciitis
Muscle
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2
Q

What host factors may predispose to developing a skin and soft tissue infection?

A

Diabetes
Immunosuppression
Renal Failure
Milroy’s Disease (congenital lymphadenopathy in legs)
Predisposing skin conditions - e.g. atopic dermatitis

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3
Q

What is impetigo?

A

A superficial skin infection common in young children that is highly infectious.

Golden crust, multiple vesicular lesions on erythematous base.

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4
Q

Where does impetigo tend to occur?

A

Exposed body parts; e.g. face, extremities and scalp

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5
Q

What organisms typically cause impetigo?

A

Usually staph aureus.

Sometimes strep pyogenes.

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6
Q

What are some predisposing factors for impetigo?

A
Skin abrasions
Minor trauma
Burns
Poor Hygiene
Insect Bites
Eczema
Chicken Pox
Atopic Dermatitis
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7
Q

How do you treat impetigo?

A

Topical Abx

For large areas may add an oral abx like flucloxacillin

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8
Q

What organism commonly causes erysipelas (upper dermis infection)?

A

Strep pyogenes

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9
Q

Where does erysipelas most commonly occur?

A

Lower limbs and then the face

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10
Q

What factors increase the risk of erysipelas?

A
Milroy's Disease
Venous Stasis
Eczema
DVTs
Obesity
Paraparesis
Diabetes
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11
Q

What is the recurrence rate of erysipelas?

A

1/3 in 3 years

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12
Q

What are the common organisms in cellulitis?

A

In most patients: 50:50 staph aureus:strep pyogenes.

In diabetics and febrile neutropenics:
About 33:33:33 staph aureus:strep pyogenes:gram negative

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13
Q

What is the typical appearance of cellulitis?

A

Spreading red area of no distinct border, fever, lymphadenopathy and lymphangitis. Shiny oedematous skin.

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14
Q

What are some predisposing factors for cellulitis?

A

Diabetes
Tinea Pedis
Lymphoedema

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15
Q

How do you treat cellulitis?

A

Cover strep pyogenes and staph aureus - can do a combination but usually just give flucloxacillin, IV vancomycin or cotrimoxazole.

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16
Q

What are 3 different types of hair associated infection?

A

Folliculitis - superficial or deep, where only one follicle is involved
Furunculosis - infection all the way to subcut that normally only involves one follicle
Carbuncles - skin abscess where multiple follicles are involved in an area

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17
Q

What does folliculitis look like?

A

Circumscribed, pustular infection of hair follicle up to 5mm in diameter.
Head, back, buttocks and extremities.

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18
Q

What is the most common organism in folliculitis?

A

Staph aureus

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19
Q

What does furunculosis look like?

A

Boils - single hair follicle inflammatory nodule extending into dermis and subcut fat.
Moist, hairy, friction-prone areas

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20
Q

What common organism is found in furunculosis?

A

Staph aureus

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21
Q

What are risk factors for furunculosis?

A
Obesity
Diabetes
Atopic dermatitis
CKD
Chronic steroids
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22
Q

Where do we typically find carbuncles?

A

Neck, posterior trunk or thigh

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23
Q

What do carbuncles look like?

A

Multiseptated abscesses

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24
Q

How do you treat hair associated infections?

A

Folliculitis/Furunculosis - leave it or topical abx. If worse then maybe oral.
Carbuncles - admit, surgical drainage, possible IV abx

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25
Q

What are some predisposing factors for necrotising fasciitis?

A
Diabetes
Surgery
Trauma
Peripheral vascular disease
Skin popping
26
Q

How many types of necrotising fasciitis are there?

A

4 - only look at 2 though

27
Q

What is type 1 necrotising fasciitis?

A

Mixed aerobic and anaerobic infection

Common in diabetic foot and Fournier’s gangrene

28
Q

What organisms can cause type 1 necrotising fasciitis?

A
Streptococci
Staphylococci
Enterococci
Gram negative bacilli
Clostridium
29
Q

What is type 2 necrotising fasciitis?

A

Monomicrobial infection - normally associated with strep pyogenes

(Very painful leg)

30
Q

What are the features of necrotising fasciitis?

A

Rapid onset
Extensive oedema and severe, unremitting pain
Haemorrhagic bullae, skin necrosis and crepitus
Systemic features, sepsis and death.
Anaesthesia at site of infection

31
Q

What is mortality for necrotising fasciitis?

A

17-40%

32
Q

What is treatment for necrotising fasciitis?

A

ABCDE - IV fluids

Surgical review
Broad spectrum abx (flucloxacillin, gentamicin, clindamycin)

33
Q

What is pyomyositis?

A

Muscle abscess normally in the lower limbs - direct progression of cellulitis or seeding of another infection (IE)

34
Q

What are common sites for pyomyositis?

A
Thigh
Calf
Glutes
Psoas
Arms
Chest wall
(Multiple sites in 15%)
35
Q

What are predisposing factors for pyomyositis?

A
Diabetes
HIV/Immunocompromised
IV drug use
Rheumatological diseases
Malignancy
Liver cirrhosis
36
Q

What organisms cause pyomyositis?

A

Usually staph aureus

other gram positives/negatives, TB, fungi

37
Q

How do you investigate pyomyositis?

A

CT/MRI

38
Q

How do you treat pyomyositis?

A

Drainage and abx

39
Q

What is septic bursitis?

A

Infection of the synovial sacs/bursae at joints close to bone, tendons and skin.
Infection often spreads from nearby skin.

40
Q

Where are the most common areas for septic bursitis?

A

Patella and olecranon

41
Q

What are some predisposing factors for septic bursitis?

A
Rheumatoid arthritis
Alcoholism
Diabetes
IV Drug Use
Immunosuppression
Renal insufficiency
42
Q

What is the most common cause of septic bursitis?

A

Staph aureus

rarer include gram negatives, mycobacteria and brucella in farmers and abroad

43
Q

What is infectious tenosynovitis?

A

Infection of the synovial sheaths around tendons - commonly in the hands, fingers and toes

44
Q

How does infectious tenosynovitis appear?

A

Red swollen semi-flexed finger that can’t move properly. Excrutiating pain on extension of finger.

45
Q

What are the most common organism in infectious tenosynovitis?

A

Staph aureus and streptococci.

Chronic - mycobacteria and fungi

If not think gonorrhoea

46
Q

What is the treatment for infectious tenosynovitis?

A

Empirical antibiotics and hand surgeon review.

47
Q

What are toxin mediated syndromes?

A

Syndromes occur as a result of toxins produced by infecting bacteria.

Superantigens produced by gram positive bacteria are a common culprit. These pyrogenic toxins stimulate T-cells directly - activating up to 20% of them and causing a massive burst of cytokine release.

48
Q

What are some consequences of the massive cytokine release in some toxin mediated syndromes?

A

Endothelial Leakage

Haemodynamic shock

Multi-organ failure

Death

49
Q

What organisms can cause toxin mediated syndromes?

A

Mostly:
Staph aureus - causing TSST1, ETA and ETB

Strep pyogenes - causing TSST1

50
Q

How do you diagnose staphylococcal TSS?

A

Fever
Hypotension
Diffuse Macular Rash
3 of (liver, blood, kidneys, GI, CNS, muscle) involved
Isolated staph aureus in mucosal/sterile sites
Production of TSST1 by isolate
Antibody development to toxin

51
Q

Where does streptococcal TSS tend to come from?

A

Deep seated infections such as erysipelas and necrotising fasciitis

52
Q

How do you treat strep TSS?

A

FAST - 50% mortality so need urgent surgical debridement of infected tissues

53
Q

How do you treat TSS generally?

A
Remove offending agent
IV fluid
Inotropes
Abx
IV immunoglobulin
54
Q

What toxin produces Staphylococcal Scalded Skin Syndrome?

A

Exfoliative toxin A or B from staph aureus

IV fluid and antimicrobials

55
Q

What tends to occur as a result of Panton-Valentine Leucocydin toxin from staph aureus?

A

Recurrent boils and haemorrhagic pneumonia in children and young adults

56
Q

What are risk factors for IV catheter associated infections?

A

Continuous infusion >24h
Cannula in situ >72h
Cannula in lower limb
Neurological/neurosurgical problems

57
Q

What common organisms are found in IV catheter associated infections?

A

MSSA and MRSA

58
Q

What are some complications of the resulting bacteraemia from seeding IV catheter associated infections?

A

Endocarditis and osteomyelitis

59
Q

How would you treat an IV cannula associated infection?

A

Remove cannula
Express pus
Abx for 14 days
Echocardiogram to be safe

60
Q

What are the 4 classes of surgical site infection?

A

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

61
Q

What can cause a surgical site infection?

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