Skin & Soft tissue infections

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Infection of the hair follicles and the apocrine regions. Small pruritic papules, topped by a central pustule. {Causes: S. aureus mostly}--- {Sites; any hair bearing region, spares palms and soles}---Spontaneous healing occurs within five days

Furuncles and carbuncles

• Furuncle ---{A deep inflammatory nodule, usually develops from preceding folliculitis} {Skin subject to friction and perspiration and containing hair follicles e.g. axillae, neck, face and buttocks} ---Carbuncle ---{More extensive, extends to the subcutaneous fat in areas covered by thick, inelastic skin---Typically nape of the neck, back or on the thighs---Associated fever and malaise} ---Cause {S. aureus} ---Diagnosis {Clinical/ pus specimen if in doubt} ---Treatment {Furuncles- Drainage} {Carbuncle- Drainage & Flucloxacillin}


♥ Vesicular, and later crusted ("golden") superficial infection of the skin ♥ Involves epidermis ♥ Occurs mainly in children
{Bacteria may produce toxin and extracellular enzymes ♥ Highly infectious ♥ Mouth or nose Mild constitutional symptoms} ~~~ {Cause ♥ S. aureus, Grp A streptococcus} ~~~ {Diagnosis ♥ Clinical evidence ♥ Culture of exudate ♥ Treatment ♥ Flucloxacillin}


{Distinctive superficial cellulitis, with prominent lymphatic involvement} ~~~{Px ♥ Painful, red, peau d'orange appearance and well demarcated border ♥ Fever ♥ Clearly defined area of demarcation} ~~~ {Cause ♥ Grp A streptococcus ♥ Uncommonly, Grp C, Grp G or Grp B streptococcus and S. aureus} ~~~ {Treatment ♥ Penicillin x 10 days}

Scalded skin syndrome

{More severe form of infection with S. aureus producing an exfoliative exotoxin} ~ {Neonates, children and rarely in adults} ~ {Splits the bridges in the skin} ~~~ {Clinical findings ♥ Widespread bullae & exfoliation with a diffuse erythematous rash ♥ Fever, hypotension, skin tenderness ♥ Bullae form and skin separates, exfoliation leads to exposed areas of bright red skin ♥ Nikolsky sign can be demonstrated} ~~~ {Mortality♥ Children - <3% ♥ Adults - up to 60%} ~~~ {Treatment ♥ Flucloxacillin to prevent superinfection}


• Notes
o Acute spreading infection of the skin that involves the subcutaneous tissues
o Assoc pain and thickening of the skin
o Previous trauma, underlying skin lesion, occasionally secondary to blood borne spread of infection
• Clinical findings
o Pain, tenderness, erythema, swelling
o Hot
o Systemically unwell
• Cause
o Strep pyogenes (Group A Beta haemolytic strep)
o Rarely Group C and G Beta haemolytic strep
o S. aureus
o Pasteurella multocida (cat/dog bites)
o Inc assoc with tinea pedis
• Diagnosis
o Clinical
o ASOT titre (high=GAS)
o Wound swab for culture & sensitivity
o Blood cultures
• Treatment (empiric)
o Flucloxacillin - 10-14 days treatment
o (fluclox and benzylpen combination often used)


• Notes
o Inflammatory collection
o Usually subcutaneous
o Involving axillae, groin and perineum
o Associted with IVDU, trauma, hospital acquired eg post operative
• Abscess - causes
o S. aureus
o also S. pyogenes
o Anaerobes - often part of mixed infections eg peri-anal abscesses
o Mycobacterium tuberculosis - atypical presentation
o Environmental mycobacteria - injection/foreign body sites
o Nocardia-immunosuppressed
o Actinomyces - traumatic/metastatic infection
o Foreign body in situ?? - Staph epidermidis
• Diagnosis
o Pus
o Gram stain
o Culture & sensitivity
• Treatment
o Incision and drainage****
o Antibiotic therapy based on c+s

Necrotising fasciitis

• Notes
o Type I
o Type II
Grp A streptococci
o Deeper infection - Characterized by destruction of skin, subcutaneous and perimuscular fat with necrotic liquefaction of fatty tissue....multi-organ failure
• Aetiology:
o Minor trauma, stab wounds, surgery
• Clinical Findings
o Severe infection, rapidly progressive
o Skin may show minimal signs of infection
Because its deeper, BUT pt would be septic on exam
o Pain, erythema, swelling, increased temperature, shiny
o Skin colour changes as necrosis develops
o Systemically very unwell
o Any part of the body can be involved
• Fournier's gangrene → Basically the same thing with perineal skin
o Full thickness necrosis of perineal skin
o May involve scrotum, penis and abdominal wall
o Severe and disfiguring
• Mortality
o Ranges from 20-47%
• Treatment
o Prompt diagnosis
o Surgical debridement
o Antimicrobial therapy
o Combination therapy e.g. benzylpenicillin, clindamycin, ciprofloxacin
o Supportive care in ITU

Gas gangrene

• Necrotizing clostridial (anaerobic) infection of devitalized subcutaneous tissue
• Cause
o Clostridium perfringens
o Spore bearing, anaerobic Gram-positive rod
o Clostridia found in faeces, manure, soil
o Occurs following falls resulting in a dirty wound or after perineal surgery
o War injuries
• Clinical features
o Acute onset
o Severe pain
o Rapid swelling and devitalization of limb - discoloration of skin (mottled)
o Appearance of fluid or gas filled blisters on skin (and radiologically)
o Systemically unwell
o Foul odour, presence of crepitus
o Bronze discolouration of the skin
o You get lysis from alphatoxin from clostridium
• Diagnosis
o CT - gas in tissues
o X-ray changes but CT a lot more definitive
o Wound swab, vesicular fluid (or wound tissue if there's debridement)
o Microscopy
o Blood cultures
o WBC raised
o Heamatocrit level is reduced
• Treatment
o Surgical exploration and debridement
o Antibiotic therapy
• e.g. clindamycin and penicillin
o ??Hyperbaric oxygen
o Supportive care in ITU

Infected burns

o Common
o Cause
Mild infection by S. aureus and Gram-negative organisms, particularly P. aeruginosa
o Can invade deeper tissues
o Pseudomonas aeruginosa can infect grafts
o Dx
Always send swab/tissue for c+s
o High mortality if bacteraemic
o Strict isolation and infection control
Because moist environment allows to replicate easily

Diabetic Foot Infections

• Notes
o Common, complex and costly
o Usually begin after minor trauma inpatients with peripheral neuropathy
o Range in severity from cellulitis to limb threatening infection

• Diabetic Foot Infections: Non-limb threatening
o Superficial, minimal cellulitis, ulceration not extending fully through skin, no significant ischaemia
o Staphylococcus aureus and β-haemolytic streptococci most common causes
o Dx
o Tx
Treat with flucloxacillin pending culture results • Limb threatening Diabetic Foot Infections: Management
o Extensive cellulitis, deep ulcers, prominent ischaemia
o Multidisciplinary approach:
• Optimize glycaemic control
• Evaluate bone and joint involvement, vascular insufficiency, gangrene, necrotising fasciitis
• Guide in choice and duration of antimicrobial agents, investigations
o Management
Deep tissue cultures specimen of choice:
Often get superficial swab and it doesn't represent!
• Aspiration
• Curettage
• Tissue biopsy
Polymicrobial aetiology (deeper):
β-haemolytic streptococci
Gram negative bacilli
o Management
Broad spectrum antibiotics pending culture and sensitivity results (previous culture reports will influence choice) eg.
• Co-amoxiclav
• Piperacillin-tazobactam
• Flucloxacillin plus ciprofloxacin plus metronidazole
o Often 1st line for deeper because ↑ in soft tissue and against gram +ve and staph aureus
Imaging (eg.MRI) to outrule osteomyelitis

3 types of Surgical Site Infection

• Clean operation wounds - refers to clean surgery that does not involve incisions through the Gastrointestinal, Resp or genitourinary tracts and is usually assoc with low infective rates.
• Clean Contaminated op wounds - refers to surgery that involves a breach of respiratory, GI or genitourinary tract and therefore presents an additional risk of contamination of wound, of e.g. removal infected appendix may result in spillage of faecalent material which subsequently cause wound infections
• Infected operation wounds - refers to operations in which the site is infected at time of surgery such as incision of abscess. Infection rates in this type of wound are naturally very high and treatment is based on culture and sensitivity of sample of pus sent to micro lab

Microbial Aetiology andfactors influencing development of SSI

o Staph. aureus
o ß haemolytic streptococci such as Group A; infectious and very invasive
o Anaerobes, Bacteroides spp., Cl perfringens
o GNB such as E. coli, Klebsiella spp., Enterobacter cloacae, Ps. aeruginosa, etc.
o Enterococci
o NB 4 & 5 more commonly colonise than infect wounds
• Factors influencing development of SSI
o Co-morbid conditions
o Duration of surgery
o Appropriate antibiotic prophylaxis
o Aseptic technique of surgical team
o Well maintained operating theatre
Regular air changes
o Post-op care..........dressing changes/hands of HCW (=exogenous)
o Drains etc. in situ/prosthesis


o Clean op wound - S. aureus/BHS most common
Flucloxacillin x7-10 days pending wound swab c+s
o Clean contaminated - as above plus GNB, anaerobes, streptococci
Co-amoxiclav pending c+s
o Contaminated wound - polymicrobial and treatment based on c+s

Erythema chronicum migrans

• Lyme disease - cutaneous manifestation
• Expanding target lesions at tick bite site
• Not all hosts develop lesions
• Diagnosis
o Serology
o Biopsy of lesion
• Treatment
o Doxycycline
o Amoxycillin


• Notes
o Multifactorial skin disorder
o Androgenic stimulation
o Excess sebaceous secretion by follicles
o Blocked sebaceous gland leads to formation of a pustule
o Secondary infection due to Propionibacterium acnes (gram + Bacillus, part of skin flora) can lead to inflammation and scarring
• Treatment
o Topical agents
o Broad spectrum antibiotics e.g. doxycycline

Animal bites

• Pasteurella multocida → bites/scratches from cats and dogs
o Cellulitis/lymphadenopathy
• Capnocytophagia → dog bites
o Anaerobes/Streptococci
• Swab/Tissue c+s
o Tetanus prophylaxis


• Notes
o Caused by papilloma virus
o DNA virus
o More common in children
o Common warts (Type 1-4) and genital warts (Type 6, 11,16&18)
o Infection by contact
o Palms / wrist / dorsum hand =types1-4
o Highly contagious
• Pathogenesis
o Infects epidermal cells
o Infected cells hypertrophy and multiply
o Keratinised nodular papilloma
• Treatment
o Childhood - self resolution
o Excision
o Salicylate and lactic acid ointment
o Freezing - cryoprobe / liquid nitrogen →5-10 seconds to burn it off


• Notes
o DNA virus
o Herpes simplex - Type I, type II
Type I - mouth and upper body
Type II - genital tract
o Infect skin and mucosa
o May be dormant following primary infection
o Reactivation occurs
• Transmission
o By direct contact
• Sites
o Gingivostomatitis
o Lip margins
o Nail bed / finger pulp (Herpetic whitlow)
o Facial skin
o Conjunctiva / cornea
o Genitalia


Varicella Zoster virus
• Varicella (Chicken pox)
o Generalised vesicular rash, especially on trunk; eventually crusts & is non-infectious at this stage
o Initial replication in respiratory tract; spread by viraemia to skin & causes successive crops of vesicles
o Virus establishes latent infection of neurons usually dorsal root & cranial nerve ganglia
• Zoster (shingles)
o Vesicular rash affecting area of sensory nerve
o Recurrence of latent varicella infection acquired earlier in life
o Preceded by pain which can persist (postherpetic neuralgia)
o If trigeminal nerve affected, may get corneal ulceration
o Unlike chicken pox, shingles can recur
• Diagnosis
o Electron microscopy
o Immunofluorescence
o Serology
o Clinical
• Treatment
o Acyclovir (topical or oral/iv if immunocompromised)
o Analgesia

Coxsackie A Virus

Coxsackie A virus
• Notes
o Coxsackie A virus - Hand, foot and mouth disease
o Highly contagious
o Blisters on hands / feet / pharynx
o Mainly children
o Short self limiting course
• Diagnosis
o Vesicular fluid, throat swab
o Viral culture, PCR

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