Bacterial Skin Infections Flashcards
What is cellulitis?
Acute infection of the lower dermis and subcutaneous (soft) tissues caused by beta-haemolytic streptococcus ± staphylococcus
=> localised area of red, painful, swollen skin, and systemic symptoms
Who is at risk of cellulitis?
*Same as erysipelas
Previous episode(s) of cellulitis
Fissuring of toes or heels, eg due to athlete’s foot, tinea pedis or cracked heels
Venous disease, eg gravitational eczema, leg ulceration, and/or lymphoedema
Injury, eg trauma, surgical wounds, radiotherapy
Immunodeficiency, eg HIV
Immune suppressive medications
Diabetes
Chronic kidney disease
Chronic liver disease
Obesity
Pregnancy
Alcoholism
What organism causes cellulitis?
Most common bacteria = Streptococcus pyogenes (2/3) and Staphylococcus aureus (1/3).
Rare causes of cellulitis include:
=> Pseudomonas aeruginosa, usually in a puncture wound of foot or hand
=> Haemophilus influenzae, in children with facial cellulitis
What is the clinical presentation of cellulitis?
Cellulitis can affect any site, most often a limb
=> Usually unilateral
=> Feeling unwell, fever, chills and rigors = first signs of illness due to bacteraemia
=> Systemic symptoms are soon followed by localised area of painful, red, swollen skin
Other signs include:
=> Dimpled skin (peau d’orange)
=> Warmth
=> Blistering
=> Erosions and ulceration
=> Abscess formation
=> Purpura: petechiae, ecchymoses, or haemorrhagic bullae
*may be associated with lymphangitis and lymphadenitis
What are the complications of cellulitis?
Severe or rapidly progressive cellulitis may lead to:
- Necrotising fasciitis (serious soft tissue infection = severe pain, skin pallor, loss of sensation, purpura, ulceration and necrosis)
- Gas gangrene
- Severe sepsis (fever, malaise, loss of appetite, nausea, lethargy, headache, aching muscles & joints, hypotention, reduced capillary refill, heart failure, renal failure)
- Infection of other organs, eg pneumonia, osteomyelitis, meningitis
- Endocarditis
How is cellulitis diagnosed?
Diagnosis based on clinical features.
Investigations may reveal:
=> Leukocytosis raised WCC
=> Raised CRP
=> Causative organism from blood culture or lesion swab culture
=> Chest X-ray in case of heart failure or pneumonia
=> Doppler ultrasound to look for blood clots (deep vein thrombosis)
=> MRI in case of necrotising fasciitis.
What is the treatment for cellulitis?
Cellulitis is potentially serious.
=> Rest and elevate the affected limb
=> Edge of the involved area of swelling should be marked to monitor progression/regression of infection
=> Benzylpenicillin + Flucloxacillin (erythromycin if penicillin allergy)
*Management of cellulitis = more complicated due to rising rates of MRSA and macrolide- or erythromycin-resistant Streptococcus pyogenes
What is the treatment for cellulitis?
Cellulitis is potentially serious.
=> Rest and elevate the affected limb
=> Edge of the involved area of swelling should be marked to monitor progression/regression of infection
=> Benzylpenicillin Flucloxacillin (erythromycin if penicillin allergy)
*Management of cellulitis = more complicated due to rising rates of MRSA and macrolide- or erythromycin-resistant Streptococcus pyogenes
What is the treatment of uncomplicated cellulitis?
No signs of systemic illness or extensive cellulitis
=> patients treated with oral antibiotics for 5–10 days or until all signs of infection have cleared (redness, pain and swelling)
=> Analgesia to reduce pain
=> Adequate water/fluid intake
=> Management of co-existing skin conditions like venous eczema or tinea pedis
What is the treatment for complicated / severe cellulitis?
Severe cellulitis and systemic symptoms treated with fluids, intravenous antibiotics and oxygen.
=> Penicillin-based antibiotics are often chosen (eg penicillin G or flucloxacillin)
=> Amoxicillin and clavulanic acid provide broad-spectrum cover if unusual bacteria are suspected
=> Cephalosporins eg ceftriaxone, cefotaxime or cefazolin
=> Clindamycin, sulfamethoxazole / trimethoprim, doxycycline and vancomycin used in patients with penicillin or cephalosporin allergy, or if MRSA infection
Treatment may be switched to oral antibiotics when the fever has settled, cellulitis has regressed, and CRP is reducing.
What is erysipelas?
Erysipelas is a superficial form of cellulitis, affecting upper dermis and extends into superficial cutaneous lymphatics.
What causes erysipelas?
Similar to cellulitis
Almost all erysipelas is caused by
=> Group A haemolytic streptococci i.e. streptococcus pyogenes
What are the clinical features of erysipelas?
=> Abrupt onset
=> Fevers, chills and shivering
=>Predominantly affects lower limb skin
=> Butterfly rash when it involves the face
=> Affected skin = very sharp, raised border
=> Bright red, firm and swollen
=> It may be finely dimpled (p’eau de orange)
=> Blistered and if severe = necrotic
=>Purpura
=> Pain and increased warmth in both cellulitis and erysipelas
What are the complications of erysipelas?
Erysipelas recurs in 1/3 of patients due to:
=> Persistence of risk factors
=> Lymphatic damage (hence impaired drainage of toxins)
Complications are rare but can include:
=> Abscess
=> Gangrene
=> Thrombophlebitis
=> Chronic leg swelling
=> Infections distant to the site of erysipelas Infective endocarditis (heart valves)
=> Septic arthritis
=> Bursitis
=> Tendonitis
=> Post-streptococcal glomerulonephritis (a kidney condition affecting children)
=> Streptococcal toxic shock syndrome (rare).
Differential diagnosis of erysipelas same as cellulitis.
How is erysipelas diagnosed?
Erysipelas is usually diagnosed by the characteristic rash. History of a relevant injury.
Tests may reveal:
=> Raised white cell count
=> Raised CRP
=> Positive blood culture identifying the organism.
=> MRI and CT are undertaken in case of deep infection.
=> Skin biopsy
