Theme 10 - clinical infections in skin tissues Flashcards by Grace Hopkinson

What are the functions of the skin?

Physical barrier - chemicals, UV, microorganismsand chemical agents
Homeostasis - thermoregulation via sweating
Immunological function - Ag presentation and phagocytosis

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Microbiology of the skin

Heavily colonised organ
Coagulase - negative staphylococci like Staph Aureus

other examples include:

propionbacterium
corynebacterium spp

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Pathogenesis of the skin - localised infection

Penetration of skin with a contaminated object

Accidental, e.g. tooth, rusty nail, knife etc.

Deliberate, e.g. surgical procedure, therapeutic injection, injection drug use

This can cause contamination of pre-existing break in the skin surface e.g. abrasion, athlete’s foot

neuronal migration of herpes complex is another route of infection too

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Pathogenesis of the skin - 2 examples of systemic/generalised infection

chickenpox

meningococcal sepsis

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What are viral warts, what are they caused by and how do they cause symptoms?

Small asymptomatic growths of skin (hands, genitals, feet, around nails, throat)

Causative agent: Human Papilloma Virus (HPV)

Pathogenesis: cause proliferation and thickening of stratum corneum, granulosum and spinosum

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Clinical presentation of viral warts, how are they treated and how can they be prevented?

Clinical presentation:

asymptomatic, mechanical,
or cervical cancer sign (HPV cause)

Treatment:
Topical- salicylic acid,
silver nitrate, cryosurgery

Prevention:
Gardasil (types 16, 18, 6 and 11);
(16 and 18 cause 70% cancer)

Genital: Barrier protection e.g. condoms

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What is a Pilonidal Cyst or Abscess?

cyst in natal cleft

caused by ingrown hair

contain hair and debris
discharge to form sinus
can present with pain, swelling and pus

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how is a Pilonidal Cyst or Abscess treated?

Hot compress, analgesia and antibiotics

Surgical excision

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What is impetigo, how does it present?

Crusting around the nares of the mouth in superficial skin

Caused by Staph aureus and is transmissible

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How is impetigo treated?

Topical antiseptics

Oral antibiotics

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What is Erysipelas?

Rash over face, raised, demarcated
Occurs in the upper dermis

Can involve lymphatics- systemic disease

Causative organism:
Strep pyogenes

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Cellulitis - what is it and what causes it?

Infection affecting the inner layers of the skin

Infection spreads from dermis and subcutaneous fat, into lymphatics
Causative agent: Bacterial
Staph aureus, Group A Streptococci
(Strep pyogenese), other B-haemolytic
Streptococci

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Pathogenesis of cellulitis

Bugs enter through breaks in skin
Wound, insect bite
Pre-existing condition eg. eczema,
Athletes foot, shingles (Zoster) etc.

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Clinical presentation of cellulitis

Rubor (red), calor (heat), dolor (pain), tumor (swelling)

Loss of skin creases, blistering, pus/exudate, fever

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how is cellulitis diagnosed? how is it treated?

Clinical, unless septic cultures rarely helpful
Exclude other causes of red hot swollen leg (eg. DVT

treated by elevation, rest, antibiotics and drainage of pus

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What is orbital cellulitis?

Infection of soft tissues around and behind eye

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pathogenesis of orbital cellulitis…

from skin or sinuses or haematogenous or trauma

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clinical presentation of orbital cellulitis

Erythema, swelling with induration

and pain on eye movement and bulging

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causative organism of orbital cellulitis and treatement

S. aureus, S. pyogenes but also
S. pneumoniae and H. influenzae

IV antibiotics

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What is necrotising fascitis?

“flesh eating bug”
There are 4 types:

Type 1: Synergistic/poly-microbial, host impairment- gram negatives,
Streps, anaerobes

Risk factors include:
Diabetes, 
obesity, 
immunosuppression, 
alcohol, 
older age group- eg. Fournier gangrene

Type 2: Group A Strep (S. pyogenese) mediated

Risk factors include:
younger age group, associated with cut or injury

Type 3:
Vibrio vulnificus-
sea water, coral

Type 4: fungal

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what is the pathogenesis of necrotising fasciitis?

Type 1:
ischaemic tissue, colonisation then infection resulting in further ischaemia and necrosis

Eg. diverticulitis, Fournier

Type 2:

infection, toxin release
disruption in blood supply
necrosis

clinical presentation of necrotising fasciitis?

Swelling, erythema (non confluent),
pain (out of context)

Crepatus, sepsis/toxaemia, necrosis, “dish water” exudate

Necrosis makes skin appear a very dark purple/red across the span of the limbs

treatment for necrotising fasciitis

Surgical emergency, debridement and antibiotics

What is gangrene?

What are the risk factors?

necrosis caused by inadequate blood supply

RISK FACTORS:

atherosclerosis
smoking
Diabetes
Autoimmune disease

What are the different types of gangrene?

Dry” vs. “Wet” Gangrene vs. “Gas” Gangrene

Pathogenesis of gangrene

Poor blood flow- tissue necrosis- colonisation- infection- synergistic infection- further necrosis

Clinical presentation of gangrene (for each type - dry, wet and gas gangrene)

Dry- “mummified”, auto-amputate Wet- boggy, swollen “dactylitis”, exudate, surrounding erythema Gas- as above but with gas in tissue- crepitus

What causes gangrene?

Skin (Staphs, Streps); Enteric (GNB, Anaerobes inc. Clostridium)

Treatment of gangrene

Surgical: source control (drainage of exudate) and revascularisation Antibiotics

What is diabetic foot infection?

Spectrum of disease from superficial through to deep bone infection in patients with Diabetes

Pathogenesis of diabetic foot infection

Damage to blood vessels - Ischaemia, impaired immunity and poor wound healing Damage to nerves- Neuropathy, trauma High blood sugars- prone to bacterial infection

Causative organisms of DFI

Superficial- skin flora: Staph aureus, Streps, Corynebacterium Deeper- skin and enteric flora: above + GNB, anerobes

Treatment of DFI

``` Surgical debridement Revascularisation Antibiotics off-loading Diabetic control ```

Pathogenesis of osteomyelitis (the 3 routes of spread)

Contiguous: eg. Diabetic foot infection Haematogenous: bugs in bloodstream Penetrating: peri-prosthetic, traumatic

Acute vs. Chronic osteomyelitis

acute: inflammatory reaction e.g. sepsis chronic: more than a month acute flares that smoulder resulting in bone death and new bone formation

new bone formation is called

involucrum

bone death is called

sequestrum

causative organisms of osteomyelitis relative to each route of pathogenesis

Haem- (children): S. aureus, Strep, Kingella, Haemophilus Contiguous: Skin (Staph, Streps) enteric (GNB, anaerobes) Penetrating: surgical- skin flora, open fracture- skin, environment Sickle cell: Salmonella sp.

Septic Arthritis - what is it?

Infection of the joint (usually bacterial but can also be cause by viruses, mycobacterium and fungi)

pathogenesis of septic arthritis

Pathogenesis: Haematogenous: blood stream infection Local spread: soft tissue, bone, bursitis Penetrating: joint injections, surgery, trauma

causative organisms of septic arthritis

``` Causative organisms: S. aureus, Streps, Haemphilus, N. gonorrhoeae, E.coli ```

clinical presentation of septic arthritis and diagnosis

Pain, swelling, erythema, reduced range of movement (unable to weightbear), Sepsis diagnosis confirmed by joint aspiration

septic arthritis is treated by

Antibiotics (guided by cultures)- 4 to 6 weeks Surgical source control: Joint washout

what is prosthetic joint infection?

infection of tissue and bone surrounding a prosthetic joint

pathogenesis of prosthetic joint infection

Pathogenesis: Bugs get onto surface of foreign body (prosthetics) immune system cannot reach- establishment of biofilm (slime) occurs Early: Implanted at time of surgery or shortly after (via wound) Late: Haematogenous but can be late presenting Early infections

Causative organisms of prosthetic joint infections

Early: Staph aureus, Staph epidermidis, Propionibacterium Late: Above and E. coli, B Haem Streps, Viridans Streps

Clinical presentation of PJI

pain instability swelling sinus and pus formation

treatment of PJI

Antibiotics alone Antibiotics with debridement Single-stage revision: remove infected joint and replace with new one at same operation Two- Stage revision: Remove old joint, given 6 weeks of antibiotics, insert new joint when sure all infection settled

How is Syphilis transmitted and what is the causative agent?

Sexually transmitted infection Caused by Treponema pallidum

Primary syphilis presents as a chancre which is...

painless, firm non-itchy ulcer at the point of contact e.g. penis tip Usually solitary Lasts 3-6 weeks Lymphadenopathy

Secondary syphilis presents as

4-10 weeks after primary Symmetrical rash that is pink, itchy and is found everywhere (even mucous membranes and soles/palms of hands and feet) - Maculo-papular or pustular - Rash contains Treponema

Tertiary syphilis presents as

3 to 15 years after initial infection in 3 forms: Gummatous, Neuro, Cardiovascular Gummatous is can be chronic causing large inflammatory swellings of skin, bone and liver.