Skin and Soft Tissue Infection

Question 1

classification of SSTI by layers of skin

Answer 1

epidermis - impetigo
dermis - ecthyma & erysipelas
hair follicles: furuncles & carbuncles
subcutaneous fat and deep dermis: cellulitis
fascia: necrotizing fascilitis
muscle: myositis

Question 2

clinical presentation of impetigo

Answer 2

localised superficial infection characterised by pustules or vesicles which then ruptured to form crusts or bullae on an erythematous base
located at the face & extremities

Question 3

clinical presentation of ecthyma

Answer 3

deeper variant of impetigo begins as vesicles/pustules –> evolve to become ulcers.
- pruitis is common.

Question 4

clinical presentation of erysipelas

Answer 4

superficial infection of the upper dermis involving the lymphatics. characterised by tender erythematous plaque with well-demarcated borders
common on face & lower extremities

Question 5

clinical presentation of furuncles & carbuncles

Answer 5

infection of hair follicles with associated small subcutaneous abscess
carbuncle: a cluster of furuncles

Question 6

clinical presentation of cellulitis

Answer 6

acute infection involving deep dermis and subcutaneous fat
- almost unilateral
- common on lower extremities

Question 7

mimickers of cellulitis:

Answer 7

deep venous thrombosis, calciphylaxis, stasis dermatitis, hematoma, erythema migrans

Question 8

the function of the skin

Answer 8

act as physical, chemical and immunological barriers against infection
- chemical: maintain acidic environment to keep microbial load low & regulate desquamation to keep transient bacteria low & sebaceous secretion inhibit growth of bacteria and fungi
- immunological: part of innate immunity & produce anti-microbial peptides to kill pathogens & normal skin commensal prevents colonisation and overgrowth of more pathogenic strains

Question 9

pathophysiology of SSTI

Answer 9

majority results from the disruption of normal host defences –> lead to overgrowth and invasion of pathogenic micro-organisms

Question 10

risk factors of SSTI

Answer 10

1. disruption of the skin barrier via
   - traumatic & non-traumatic
   - reduced venous & lymphatic drainage due to obesity, saphenous venectomy, chronic venous insufficiency
   - peripheral artery disease
   - age
   - physical environment (pH, soap and detergent use, humidity & moisture)
2. medical conditions: (DM, cirrhosis, neutropenia, HIV)
   3 drugs: immunosuppressive agents & SGLT2i
3. history of cellulitis

Question 11

prevention of SSTI:

Answer 11

• good care to maintain skin integrity
• identity and treat predisposing factors at the time of initial diagnosis to decrease the risk of occurrence
• acute traumatic wounds should be copiously irrigated & remove foreign objects & debride devitalised tissue

Question 12

when culture is needed for SSTI?

Answer 12

mild and superficial infections no need (eg. impetigo, ecthyma)

Question 13

What can lead to disruption of the skin barrier

Answer 13

• traumatic injury
• non-traumatic
• reduced venous and lymphatic drainage
• peripheral artery disease
• advanced age
• physical environment (eg. pH, soap, detergent, moisture, urine, feces, sweat, chronic wound fluid)

Question 14

what are some conditions can lead to a reduced venous & lymphatic drainage

Answer 14

saphenous venectomy, obesity, chronic venous insufficiency

Question 15

conditions predispose to SSTI

Answer 15

diabetes, cirrhosis, neutropenia, HIV, history of cellulitis

Question 16

drugs predispose to SSTI

Answer 16

immunosuppressants, SGLT2i

Question 17

how should the sample be taken for culture?

Answer 17

• from deep in the wound after the surface cleansed
  ==> bc surface may be contaminated
• from the base of a closed abscess where bacteria grow
• by curettage, rather than wound swab or irrigation
  ==> bc difficult to obtain representative samples from wound swabs

Question 18

what culture is needed?

Answer 18

• cultures of pus, exudates or tissues from the wound
• blood culture (for severe cases with marked systemic sx of infection or immunocompromised pt)

Question 19

what conditions are considered as purulent

Answer 19

furuncles, carbuncles, skin abscesses, purulent cellulitis

Question 20

clinical presentaitons of skin abscess

Answer 20

collection of pus within the dermis and deeper skin tissues. manifest as painful, tender fluctuant and erythematous nodules

Question 21

complications of cellulitis

Answer 21

more common in immunocompromised patients
- bacteremia, endocarditis, toxic shock, glomerulonephritis, lymphedema, osteomyelitis, necrotising soft-tissue infection

bc infection is usually caused by gram pos which likes to stick to heart, joint, spine & release toxins that cause accentuated response to go into sepsis & shock

Question 22

pathogens need to cover for impetigo

Answer 22

staphylococci or streptococci, MSSA
toxin producing strain of S.aureus cause bullous

Question 23

pathogens need to cover for ecthyma

Answer 23

group A streptococcus (S.pyogenes), MSSA

Question 24

coverage for non-purulent cellulitis, erysipelas

Answer 24

mainly beta-hemolytic streptococcus (S.pyogenes), MSSA cover for moderate
Water exposure: aeromonas, vibrio vulnificus, pseudomonas aeruginosa

Question 25

coverage for purulent infection

Answer 25

• mainly S.aureus.
• some beta-hemolytic strep
• gram-neg & anaerobe (common in patients with skin abscess involving perioral, perirectal or vulvovaginal areas)
• HA-MRSA (depends on the risk factors)

Question 26

definition for HA-MRSA

Answer 26

infection occurs >48 hours after hospitalisation OR outside of hospital within 12 months of exposure to healthcare

Question 27

empiric treatment for impetigo ecthyma with multiple lesions

Answer 27

PO cephalexin or cloxacillin
PO clindamycin if penicillin allergy
duration for 7 days (severe:10-14 days)

Question 28

culture-directed (S.pyogenes) treatment for impetigo & ecthyma

Answer 28

PO penicillin V and amoxicillin

Question 29

culture-directed (MSSA) treatment for impetigo & ecthyma

Answer 29

PO cephalexin or cloxacillin

Question 30

treatment for mild impetigo

Answer 30

often self-limiting.
can give topical mupirocin BD x 5d or tropical tetracycline