Skin and soft tissue infections

Question 1

What are the main organisms that colonise the skin?

Answer 1

• Coagulase-negative Staphylococci
• S Aureus
• Propionibacterium (e.g. Acnes)
• Corynebacterium

Question 2

What is the pathogenesis of skin infections?

Answer 2

Inoculation

• penetrate skin with contaminated objects
• Contamination of pre-existing breach in skin surface

Other route - neuronal migration in herpes simplex

Systemic/generalised infection

Question 3

What viral infections cause skin infections?

Answer 3

Herpes simplex virus

VZV - shingles

Molluscum contagiosum

Cow pox - first virus to be vaccinated

Orf- sheets/goats - purulent producing papule

Question 4

What is the pathogenesis of the HSV?

Answer 4

Vesicle formation -> ulceration -> weeping vesicular lesions (virus release)

Gains entry through sensory nerve endings and remains in dorsal root ganglion

Latent = episome - no immune repose

Reactivation - migrates downward to sensory root ends and manifests

Question 5

What are the two types of HSV infection

Answer 5

Primary - occurs once - usually in infancy, extensive painful lesions in mouth

Secondary - occurs time again - weeping vesicles (peri oral and genital)

Question 6

What triggers a reactivation infection of HSV?

Answer 6

Stress or infection

Question 7

What is the type of herpes that MAINLY causes a) mouth herpes; b) genital herpes

Answer 7

HSV1 (mouth)

HSV2 (genital)

Question 8

How his herpes simplex virus diagnosed?

Answer 8

Clinical usually

Vesicle fluid releases virus (PCR detection of viral DNA)

Question 9

What is the treatment fora) cold sores and b) genital herpes

Answer 9

a) topical acyclovir

b) oral acyclovir

Question 10

What is the primary and secondary manifestations of VZV

Answer 10

a) chicken pox

b) shingles

Question 11

How does latent infection of VZV present?

Answer 11

Shingles - weeping vesicular rash

Dermatome distribution

Question 12

How is VZV diagnosed?

Answer 12

Clinical

Vesicle fluid - PCR VZV DNA

Question 13

What is the treatment for shingles

Answer 13

Acyclovir/valacyclovir - Oral/IV

Question 14

How does the molluscum contagiosum virus present?

Answer 14

Raised PEARLY lesions

Umbilicated

Question 15

How is molloscum contagious diagnosed?

Answer 15

Clinical - very simple

Question 16

What is the treatment for molloscum contagiosum treated?

Answer 16

None - usually disappear with 6-18 months

Question 17

What are the main causative organisms for bacterial skin infections?

Answer 17

Staph Aureus
Strep Pyogenes

Also H influenzae, pasteurella multocida (cat/dogs)

Question 18

What type of bacteria is staph areus? What exotoxins does it produce that are important in the context of skin infections?

Answer 18

Gram positive- normal nasal flora (30% pop)

• epidermolytic toxin A and B (ETA/ETB)
• Toxic shock syndrome toxin
• Paton valentine leucocidin (PVL)

Question 19

What is the main action of strep pyogenes?

Answer 19

Haemolytic

Question 20

What is the causative bacteria that cause impetigo?

Answer 20

S aureus

S Pyogenes

Question 21

How does impetigo present?

Answer 21

Usually on face (around nose -mainly children) - infection of epidermis

Plaque-like lesions
Yellowish exudate
Thick scabs - honey comb lesions

Question 22

How is impetigo diagnosed?

Answer 22

Clinical

Bacterial culture

Question 23

What are the complications of impetigo? What is the pathogenesis?

Answer 23

Bullous impetigo

Staphylococcal scalded skin syndrome (SSSS)

Exotoxin - Epidermolytic toxin A&B

Question 24

What area of skin and bodily areas mainly is effected by erysipelas?

Answer 24

Dermis

Face and shin

Question 25

What is the causative bacteria for erysipelas?

Answer 25

S Pyogenes

Question 26

How does erysipelas present?

Answer 26

Lymph node enlargement Fever and malaise Well demarcated inflamed lesion - red, swollen, painful, hot

Question 27

What is cellulitis?

Answer 27

Infection of the skin and subcutaneous tissue?

Question 28

What are the causative organisms for cellulitis?

Answer 28

P Aureus S Pyogenes H influenzae Pasturella multocida (animal bites)

Question 29

How does cellulitis present?

Answer 29

Site of inoculation (portal of entry may not be observable!) Diffuse enlargement - not well demarcated - erythema (redness), swelling, tenderness, hot Any part of body - UNILATERAL Fever and malaise

Question 30

How is cellulitis diagnosed?

Answer 30

- Clinical diagnosis - Unilateral (discount bilateral differentials) - Lesion swabs - Blood cultures (rare though)

Question 31

What is the pathogen causing anthrax?

Answer 31

Bacillus anthracis | - spore forming aerobic gram positive

Question 32

Where is the source for anthrax?

Answer 32

Imported wool, hides, hair, drum skins

Question 33

What is the pathogenesis of anthrax?

Answer 33

Inoculation through breaks in the skin

Question 34

How does anthrax present?

Answer 34

Malignant pustule

Question 35

When is anthrax lethal?

Answer 35

If inhaled/septicaemic Cutaneous = readily treated

Question 36

What are the two types of necrotising fascitis and what bacteria causes them?

Answer 36

Type 1 - polymicrobrial - anaerobes, gram negative bacilli (from large bowel) Type 2 - strep pyogenes

Question 37

How does necrotising fascitis present?

Answer 37

Dark, rapidly spreading necrotising lesion Fever and malaise (very sick!)

Question 38

What is the treatment of necrotising fascitis?

Answer 38

IV antibiotics | Surgical debridement

Question 39

What is the causative organism for gas gangrene?

Answer 39

Clostridium perfrinigens - anaerobic gram positive Dirty lower GI procedures/limb amputation

Question 40

How does gas gangrene present and whats its treatment?

Answer 40

Subcutaneous gas Dark rapidly spreading necrotising IV antibiotics and limb debridement

Question 41

When should topical/ora/IV antibiotics be used?

Answer 41

Topical - superficial infections e.g. impetigo erysipelas Oral/IV = more severe - cellulitis/necrotising fascitis/gas gangrene etc

Question 42

What is the treatment for staph aureus/strep pyogenes

Answer 42

Penecillin (flucloxacillin) Allergy -erythromycin/calrithromycin vancomycin, linezoid MRSA - vancomycin, linezoid

Question 43

What antibiotics are used to treat anaerobic infections?

Answer 43

Metronidazole

Question 44

What antibiotics should we use for necrotising facilities?

Answer 44

Meropenem | Clindamycin

Question 45

What are skin fungal infections referred to as? What is there pathogenisis

Answer 45

Dermatophyte infections Use keratin as nutritional substrate

Question 46

What are the name of dermatophyte infections?

Answer 46

Skin - Tina corporis - Tina pedis (athletes foot) ``` Scalp Tina capitus (ring worm) ```