Summary Infectious diseases covering all core conditions from the medicine syllabus

Skin and soft tissue infections
Thursday, 29 September 2022
09:49
CELLULITIS

Non-necrotising inflammation of dermis, subcutaneous tissue usually
caused by Strep aureus/ pyogenes. Commonly face, legs and arms.

Types:

 Purulent
o Furuncles, carbuncles, abscesses, cysts
 Non-purulent
o Superficial cellulitis, erysipelas

Risk factors:

 Skin inflammation
 Lowered immunity
 Skin infection
 Oedema
 Obesity

Signs & symptoms:

 Fever, chills
 Localised inflammation
o Swelling
o Warmth
o Erythema with unclear borders
o Pain
 Enlarged lymph nodes

Diagnosis:

 Ultrasound
o Subcutaneous fat separates into lobules
 Cobblestone appearance
Lab results:

 Complete blood count (CBC)
o Raised inflammatory markers
o Raised CRP
o Raised ESR
o Raised WBC
 Wound, blood cultures
o Identify causative microbe

Treatment:

 Medications:
o Antibiotics: second generation Penicillins, first generation
cephalosporins, vancomycin for MRSA

,  Other interventions:
o Immobilisation, elevation, dressings
o Drain abscess

NECROTISING FASCIITIS

Progressive life-threatening infection caused by progressive destruction of
deep soft tissue. Bacteria spread via subcutaneous tissue -> release
exotoxins -> tissue destruction spreads along fascial planes. Commonly
caused by Group A Strep (Strep pyogenes). Most commonly affects the
perineum (Fournier's gangrene)

Risk factors:
 Diabetes mellitus
 IVDU
 immunosuppression

Symptoms:
 Intense pain over affected skin and underlying muscle (pain out of
keeping with pain out of keeping with physical features)

Management:
 Urgent surgical debridement +- amputation
 Drugs: IV antibiotics e.g. benzylpenicillin and clindamycin

ERYSIPELAS

Acute, non-necrotising infection of upper dermis and superficial
lymphatics. Butterfly shaped inflammation on the face. Usually caused by
strep pyogenes.

Complications:
 Lymphoedema due to impaired lymphatic drainage
 Necrosis
 If spread to areas it may cause arthritis, osteomyelitis, necrotising
fasciitis, glomerulonephritis

Signs & Symptoms:
 Initially fever, chills, headache, fatigue
 Lesions mostly on legs, face and arms
 Elevated warm painful rash reddest at the border
 Lymphadenopathy

Diagnosis:
 Lab results:
o Raised CRP, raised ESR, raised WBC

Treatment:
 Oral Penicillins/ macrolides
 Vancomycin if MRSA
 IV if severe

IMPETIGO

,Highly infectious skin infection affecting superficial epidermis. Commonly
found in children. Can spread by skin-skin contact. Spread over the body
through scratching. Commonly S.aureus and S.pyogenes.

Signs & symptoms:
 'Golden' crusted skin lesions typically around the mouth
 Very contagious

Diagnosis:
 Lesion culture
 History
 Physical exam

Treatment:
 Penicillins
 Topical antibiotics

OSTEOMYELITIS

Infection of often trabecular bone that may spread from boils, abscesses,
pneumonia, or genitourinary instrumentation.

Pathology:
 Infection-> cortex erosion with holes. Exudation of pus lifts
periosteum interrupting blood supply -> necrosis.
 Adults - commonly seen in vertebrae (IVDU) and feet (diabetics)
 Children - vascular bone (long-bone metaphases - distal femur,
upper tibia)


Categories:
 Acute haematogenous
 Secondary to contiguous local infection +- vascular disease
 Direct inoculation from trauma or surgery

Organisms:
 Mainly Staph. Aureus
 Pseudomonas
 E. coli
 Streptococci
 Less common include:
o Salmonella
o Mycobacteria
o Fungi

Acute features:
 Gradual onset pain
 Unwillingness to move over a few days
 Tenderness
 Warmth
 Erythema
 Effusion in neighbouring joints

Complications:

,  Fractures
 Septic arthritis
 Deformity
 Chronic osteomyelitis

Tests:
 Raised CRP/ESR
 Raised white cell count
 Blood culture accurate in 60%
 Gold standard - bone biopsy and culture - rarely for acute OM
 After 10-14 days X-rays may show haziness +- loss of density
 MRI is sensitive and specific

Acute treatment:
 Drain abscesses, remove sequestra (culture)
 6 weeks of antibiotics:
 Vancomycin and cefotaxime 1g/12h until MC&S known
 Fusidic acid + Clindamycin for adults?
 Ciprofloxacin PO for Pseudomonas

CHRONIC OSTEOMYELITIS
Poor treatment -> pain, fever, sequestra and sinus suppuration with long
remissions. Always suspect chronic OM in vascular insufficiency with non-
healing tissue ulceration over bony prominences.
Treatment:
 Excision of sequestra
 Skeletal stabilisation
 Antibiotics - 12 weeks




Healthcare-associated infection
Tuesday, 18 October 2022
18:25
Types:
 Catheter-associated UTI
 Infection associated with intravascular access devices
o Staph. Epidermidis, Staph. Aureus (MRSA/MSSA), Candida,
enterococci
 Ventilator-associated pneumonia
o P. aeruginosa, Enterobacteriaceae, Staph. Aureus
o Suspect if new/persistent infiltrates on CXR plus 2 or more of: