Skin and Soft Tissue Infection

Question 1

What are the natural defences of the skin?

Answer 1

• Barrier- keratin
• Acidic sebaceous secretions
• Immune response via blood supply and lymphatics
• Mucosal lysozymes, IgA, washing secretions
• Normal flora
• • Coag negative staphylococci, staph. aureus, Corynebacterium sp., Propionibacterium sp., Candida sp. (fungus)

Question 2

Describe colonisation

Answer 2

• Does not mean infection
• Infection involves signs of inflammation
• > Fever, swelling, redness, pain, loss of function
• In leg ulcer, surgical wounds, IV- line sites
• At this point, treat patient not microbiology

Question 3

How might the skin change in systemic disease?

Answer 3

• Rashes
• Vesicles, macules, papules
• Vasculitis, embolic, haemorrhagic lesions

Question 4

What does SSSI stand for?

Answer 4

• Skin and Skin Structure Infections

Question 5

What does SSTI stand for?

Answer 5

• Skin and Soft Tissue Infections

Question 6

What does ABSSSI stand for?

Answer 6

• Acute Bacterial Skin and Skin Structure Infections (ABSSSI)

Question 7

What are the causative agents of skin infections?

Answer 7

• Staph aureus (MRSA, MSSA)
• Streptococci (beta haemolytic)
• Anaerobes
• Coliforms
• Other gram negative, e.g. dog bites
• Fungal
• Viral features
• Parasites

Question 8

Describe the infection Impetigo (epidermis)

Answer 8

• Usually confined to face
• Vesicels/pustules on erythematpus base
• Becomes crusty, yellow oozing lesions
• Bullous or non-bullous (large pocket of fluid)
• Contagious
• Diagnosis: clinical (can take swab for culture and sensitivities)
• Treatment: topical antibiotics or systemic agents, flucloxacillin

Question 9

Describe the infection Erysipelas (intradermal infection)

Answer 9

• Sharply dermarcated raised edge
• Patient was systemically well otherwise
• Swabs all post antibiotics no growth
• Antistreptolycin O (ASO) titre 1600
• Streptococci beta-haemolytic (strep pyogenes)

Question 10

Describe infection Cellulitis (loose subcutaneous tissue/risk factors)

Answer 10

• Staph aureus/strep. cocci beta-haemolytic (strep pyogenes)
• Risk factors: DM, trauma, dermatitis, peripheral vascular disease
• • Marker outline to check spread
• • Response to antibiotics
• Those with chronic skin conditions are more likely to develop secondary bacterial infections

Question 11

Describe infection Lymphangitis

Answer 11

• Group A streptococci beta-haemolytic (strep pyogenes)

Question 12

Describe abcesses

Answer 12

• Furunculosis infected hair follicles
• Carbuncles Toxaemia
• Sebacious or sweat glands
• Staph aureus including MRSA
• Drain abcess
• Could be multifunctional
• Acidic environment, therefore antibiotic activity limited

Question 13

Describe bacterial toxins

Answer 13

• Toxic shock syndrome
• Scaled skin syndrome
• PVL toxin

Question 14

Describe possible investigations for SSTIs

Answer 14

• Diagnosis often clinical
• Blood counts and markers
• Swabs, pus
• Blood culture if febrile or septic
• Serology, e.g. ASO titre
• Imaging (GAS) or extent of damage
• Debrided tissue

Question 15

Give examples of some deeper infections

Answer 15

• Necrotising infections (anaerobes often involved)
• > Gas gangrene
• > Necrotising fasciitis (flesh-eating bacteria)
• Pyomyositis

Question 16

Describe ‘Cat-scratch disease’

Answer 16

• Bartonella henselae

Question 17

Describe lyme disease

Answer 17

• Erythema chronicum migrans

- Tick bite

Question 18

Give examples of other unusual bacteria

Answer 18

• Cutaneous mycobacteria (similar to TB)
• Fish tank granuloma, M. marinum
• Buruli ulcer, M. ulcerans
• Leprosy, M. leperae

Question 19

What empirical treatment may be used to treat SSTIs?

Answer 19

• Clinicians used 54 different antibiotic agents in initial management of skin infections
• 40% of patients had modification of antibiotics of which majority were due to treatment failure
• Around 70% of cases already on antimicrobials 3 months prior to hospitalisation

Question 20

Describe cryptic antibiotic resistances in S. aureus

Answer 20

• Resistant organisms appear to be sensitive to a particular antibiotic phenotypically and can escape routine diagnostic tests

Question 21

Describe viral infections of the skin and mucosae

Answer 21

• HSV, VZV (HZV), CMV, EBV
• Herpes
• Primary lesion, systemic in chicken pox
• Spread up sensory axons to ganglion, latent infection
• Reactivation results in cold sore (HSV1) or shingles (HSV)
• Treatment for serious cases acyclovir, valaciclovir or famiciclovir

Question 22

What are other viral infections of the skin and mucosae?

Answer 22

• Papilloma virus- warts
• Hand, foot and mouth- enteroviruses (may lead to diarrhoea)- pharyngitis and vesicles that burst leaving 5-10 oral painful ulcers, simultaneous lesions on hands and feet
• Molluscum contagiosum- direct and sexual contact
• Orf- more common in vets and butchers due to exposed animal contact
• Small pox
• Measles

Question 23

Describe higher organisms

Answer 23

• Protozoa (cutaneous leishmaniasis)- satellite region
• Mites, e.g. scabies- benzyl benzoate used
• Insects
• • Lice, fleas, maggots and larva