Skin and soft tissue infection

Question 1

What is an SSTI?

Answer 1

-Skin and soft tissue infection
-Bacterial infection of the dermis and subcutaneous tissues

Question 2

Examples of SSTI

Answer 2

-Impetigo
-Ecthyma
-Cellulitis
-Erysipelas (lymphatics)
-Furuncle/ carbuncle
-Erysipeloid
-Ascending lymphangitis
-Necrotising fasciitis
-Gas gangrene
-Fournier’s gangrene
-Toxic shock syndrome

Question 3

SSTI Disease Burden

Answer 3

-Common
-Incidence wide ranging up to 24.6/1000 person years

Question 4

Clinical spectrum of SSTI

Answer 4

• Common generally mild infections which are relatively easy to treat as outpatient- I&D alone +/- oral antimicrobials
  -Moderate infections (OPAT- IV)
  -Severe infection (cSSTI) associated with systemic toxicity (SIRS), severe local pain, bullae formation, haemorrhagic appearance, gas, rapid spreading margins

Question 5

What is involved in a severity assessment?

Answer 5

-History
-Vital signs (systemic involvement), extent of local involvement
-qSOFA, SIRS

Question 6

What investigations are required for moderate to severe SSTI?

Answer 6

-Routine haem, biochem, inflammatory markers, lactate, CK, glucose
-Plain film X-ray= gas, foreign body
-Surgical review early if indicated

Question 7

What is involved in diagnostic microbiology?

Answer 7

-I&D abscess; swab of discharging material
-Blood cultures= systemic features/ pre IV antibiotics

Question 8

Sepsis 6

Answer 8

1. Deliver high-flow oxygen
2. Blood cultures prior to admin of antibiotics
3. Administer empiric intravenous antibiotics
4. Measure serum lactate and FBC
5. Start IV resuscitation
6. Commence accurate urine output measurement

Question 9

Describe the microbial spectrum

Answer 9

-85% Group A Streptococcus (S pyogenes) (B.C.G)
-Staphylococcus aureus (incl MRSA)
=Blood cultures positive <5%
=Needle aspiration 5-40%
=Punch biopsy 20-30%

-Myriad other pathogens in specific clinical settings/ risk hosts: require consideration/ diagnosis: aspirate/ skin biopsy
=wounds, water exposure, bites, injection drug use

Question 10

Describe necrotising fasciitis and treatment of it

Answer 10

-Severe/ disproportionate pain, woody tissue
-Finger test
-Systemic toxicity, mortality =10% (up to 50-70%)

-Failure to respond to antimicrobial initiation
-Requires broad spectrum high dose parenteral therapy
-Clindamycin adjunctive anti-toxin effect and modulation of cytokines
-Surgical debridement often required and should not be delayed- therapeutic and diagnostic
-Potential role for IVIG (immunoglobulin) in STSS

Question 11

Most appropriate initial antibiotics for necrotising fasciitis

Answer 11

-Amoxicillin
-Piperacillin/ Tazobactam
-Ciprofloxacin
-Phenoxymethylpenicillin (Pen V)
-Flucloxacillin IV (!)

Question 12

Antibiotics and considerations for Impetigo

Answer 12

-Flucloxacillin 0.5-1.0g qds po
-Clarithromycin 500mg bd po

Considerations:
-limited: top mupirocin
-Clindamycin po an alternative

Question 13

Antibiotics and considerations for Erysipelas (Strep)

Answer 13

-Amoxicillin/ Flucloxacillin/ Clarithromycin/ Cephalexin po

Considerations: benzylpenicillin 2.4g 4-6hrly IV

Question 14

Antibiotics and considerations for MSSA Cellulitis

Answer 14

-Mild: oral flucloxacillin/ clarithromycin
-Severe: flucloxacillin

Considerations: Doxycycline, co-trimoxazole, clindamycin alternatives

Question 15

Antibiotics and considerations of MRSA

Answer 15

-Vancomycin

Considerations: oral alternatives (doxycycline, co-trimoxazole, clindamycin)

Question 16

Antibiotics and considerations of Necrotising fasciitis

Answer 16

-Flucloxacillin/ benzylpenicillin/ clindamycin/ gentamycin/ metronidazole

Considerations: polymicrobial infection requires empiric broad spectrum coverage IV

Question 17

Length of antibiotic duration for SSTI

Answer 17

-Mild 7 days
-Mod/Severe 10-14 days, definite clinical improvement

Question 18

Sites of SSTI involvement

Answer 18

-Lower limb most common
-Face
=Preseptal cellulitis
=Peri-orbital cellulitis: deeper involving tissues of orbit (CT scan)

-Hands
-Soft tissue overlying joints

Question 19

Host predispositions to SSTI

Answer 19

-DM
-Peripheral vascular disease
-Lymphoedema
-Obesity
-Prior episodes
-Skin disease (eczema, psoriasis)
-Immunocompromised (fungal, atypical mycobacteria)
-Malignancy
-Chronic liver disease
-Tinea pedis/ onychomycosis

Question 20

Risk factors for recurrent SSTI/ cellulitis

Answer 20

-DM
-Obesity
-Fungal infection
-Lymphoedema

Question 21

Streptococcal species recurrent SSTI/ cellulitis

Answer 21

-Rapid onset at previous site
-1/3 recur
-Prevent: skin care, weight loss, manage oedema
-Prophylaxis: 3 episodes/ year- Pen V/ Macrolide

Question 22

Staph aureus recurrent SSTI/ cellulitis

Answer 22

-Different sites
-Purulent skin infections: I&D
-Decolonise

Question 23

What does recurrent SSTI mimic?

Answer 23

-Skin disease= varicose eczema, drug eruption, dressing reaction, GvHD
-Zoster
-Erythema multiforme
-Erythema nodosum
-Gout
-DVT
-Ruptured bakers cyst

Question 24

Describe clostridium spp infection

Answer 24

-Exposure: wound contam IDU (spores)
-Clinical syndrome: gas gangrene, myonecrosis
-Considerations: massive tissue oedema, V high WCC

Question 25

Describe pseudomonas aeruginosa infection

Answer 25

-Exposure: water, hot tub
-Clinical syndrome: Whirlpool folliculitis, ecthyma, gangrenosum
-Considerations: immunocompromised

Question 26

Describe vibrio vulnificus infection

Answer 26

-Exposure: saltwater, fish handling
-Clinical syndrome: gas gangrene, myonecrosis
-Considerations: liver disease, Fe overload, malignancy

Question 27

Describe Pasteurella spp infection

Answer 27

-Exposure: dog/ cat bite/ wound
-Clinical syndrome: cSSTI
-Considerations: Short incubation

Question 28

Describe anthrax infection

Answer 28

-Exposure: IDA, textile workers
-Clinical syndrome: massive oedema/ tissue necrosis/ local oedema/ eschar
-Considerations: debridement