Skin & Soft Tissue Infections (SSTI) Flashcards
What tissues soft tissues of the body can become infected?
- Skin at various levels (most common)
- Connective tissues
- Nerves e.g. herpes, leprosy and poliomyelitis
- Muscle e.g. bacterial/viral myositis (rare)
- Blood vessels e.g. syphilis, typhus, viral vasculitis, endocarditis and vascular prosthesis infection (rare)
What connective tissue structures can become infected?
Widely spread:
- Fibrous tissues
Rarely infected:
- Fascia e.g. necrotising fasciitis
- Fat
- Tendons
- Ligaments
- Synovial membranes e.g. infective synovitis or bursitis (looks like joint infections due to close proximity)
What is the difference between impetigo and erysipelas?
Both infections of epidermis but impetigo is usually caused by staphylococcus but erysipelas is normally caused by streptococcus
What is cellulitis?
Skin infections of the dermis +/- subcutaneous fat either due to staphylococcus or streptococcus - can surround carbuncles/furuncles
What is a furuncle?
Deep infection of a hair follicle i.e. a ‘boil’ usually caused by staphylococcus - can be surrounded by cellulitis
What is a carbuncle?
Connecting collection of furuncles or ‘boils’ that is also usually caused by staphylococcus - can be surrounded by cellulitis
What is necrotising fasciitis?
Deep infection of the fascia +/- muscle usually caused by streptococcus or mixed bacteria - can be caused by cellulitis getting deeper than the dermis and subcutaneous fat
What viruses can cause skin and soft tissue infections?
- Viral warts: skin warts, verruccas, genital warts
- Herpes: herpes simplex 1 (oral) and 2 (genital), herpes labialis, herpes genitalis
- Viral exanthems: chickenpox, shingles, measles
- Molluscum contagiosum
- Small pox
What bacteria cause skin and soft tissue infections?
- Streptococcus
- Staphylococcus aureus
- Opportunistic bacteria e.g. in diabetic foot ulcers
What fungi cause skin and soft tissue infections?
- Tinea infections: tinea pedis (Athlete’s foot), tinea corporis (ring worm)
- Seborrhoeic dermatitis: dandruff
What other organisms cause skin and soft tissue infections?
Protozoa: cutaneous leishmaniasis
Helminths: cutaneous larva migrans e.g. dog parasite crawling through skin (need anti-worm tablets)
Ectoparasites: scabies and cutaneous myiasis (e.g. botfly) that remain on superficial skin
How should you clinically describe a skin lesion?
Shape Size Edge Colour Surface Distribution
What is the characteristic colour of an impetigo lesion?
Golden
What are the 3 stages of chicken pox/shingles skin lesions?
- Papule
- Blister
- Ulcer
How can you get impetigo?
Poor hygiene
Rugby playing
How do you treat carbuncles?
Antibiotics
Incision drainage surgery
Where does necrotizing fasciitis tend to occur?
In limbs due to blunt trauma or pelvic area due to operation
How do you treat necrotizing fasciitis?
Patient will be septic so surgically removing the skin on top of the fascia to keep patient alive (can sometimes be down to tendons and bones)
What will ring worm lesions present like?
Round red mark
Itchy
Flaky
What would cutaneous leishmaniasis skin infection present like?
Skin lesion with raised edge with ulcerated area in middle but not as painful as you’d expect (disappears with long-term antibiotics)
Who is scabies most likely to effect? How would it present?
In people whose hygiene is compromised presenting with scabby, scaly skin and burrows and scabies can be noticed if you look close enough, intense itching in finger webs that’s worst at night and in hot baths so you need to improve hygiene of the patient along with topical solution
What is a symbiotic relationship?
Close and often long-term interaction between 2 different species that can be mutualistic, commensal or parasitic e.g. commensal is where 1 species derives some benefit whilst the other is unaffected
What is colonisation?
When a microbe grows on or in another organism w/o causing any disease
What is an infection?
Invasion and multiplication of microbes in an area of the body where they are not normally present which usually leads to disease - may cause no symptoms, be sub-clinical or cause varying degrees of symptoms and be clinically apparent
What is a pathogen?
Microbe able to cause disease
What areas of the body are densely populated by microorganisms? What areas are sparsely populated or sterile?
Densely populated:
- Oral cavity
- Distal region of urethra
- Vagina (mainly lactobacilli)
- Colon
- URT
Sparsely populated:
- Skin (gram +ve species)
- Stomach
Sterile:
- Lungs
- Internal tissues
- Urinary tract
How is the population of an area of the body in terms of microorganisms classified?
In aerobic organisms per cm squared:
10^2 = dry
10^7 = moist
Cutaneous flora may be ___ or ___ (e.g. ___).
Resident
Transient
MRSA
How is staphylococcus epidermidis normally classified along with other staphylococcus species (not S. Aureus)?
Commensal coagulase -ve bacteria that colonise the skin of nearly all humans and are usually non-pathogenic causing infections only if they reach internal prosthetic material
How is staphylococcus aureus normally classified?
As a pathogen that may colonise skin esp. if a patient has poor hygiene or abnormal skin but still need to invade and multiply to cause infection so remain commensal until that happens - ‘de-colonisation’ treatment to sterilise skin may be beneficial
What do cultures of staphylococcus aureus typically look like?
Golden in colour
What is the pathogenesis of skin and soft tissue infections (SSTIs)?
- Access: most bacteria already found on skin as colonisers
- Adherence: well-developed adhesin molecules allow colonisation
- Invasion: most need a skin break but PVLSA and GAS are highly invasive
- Multiplication: colonisation of skin/wounds may precede infection
- Evasion: staph catalase blocks free radicals whilst the strep M protein blocks complement
- Resistance: many bacteria causing SSTIs have drug resistance e.g. MRSA
- Damage: affects epidermis, dermis, deeper tissue and can lead to septicaemia
- Transmission: easily passed from skin by direct or indirect contact
What are the risk factors for skin and soft tissue infections?
Direct inoculation (e.g. trauma, medical procedures and skin ulcers) Previous colonisation (e.g. poor hygiene, S. Aureus or MRSA) Immunosuppression (e.g. DM and renal failure)
What is PVLSA?
Panton Valentin Leukocidin Staphylococcus Aureus - particularly aggressive as it has a special chemical that kills WBCs so spreads through blood and organs rapidly with high mortality
How should you diagnose a skin and soft tissue infection?
- History: PC, HPC, PMH, ADT, FH, SH and ROS - check for risk factors
- Exam: general, CVS, RS, abdo, NS, LMS, skin, etc. - check if its localised
- Differential diagnosis
- Investigations: bed side, body samples, imaging, physiology and histopathology
- Diagnosis
- Treatment
What microbiology investigations can be carried out for a skin or soft tissue infection?
- Swabs: pus (e.g. from boil but clean surface 1st then push more pus out) or skin - look for colonisation in nose and throat e.g. S. Aureus
- Body fluids: pus, vesicle fluid and blood
- Body tissues: biopsies rarely
What information can you get from a swab?
Resistance/sensitivities to antibiotics (Meticillin used in lab as marker for multi-resistance)
Genetic testing can tell you whether its VPL +ve
How can you look for more deeply seated infections?
Radiology e.g. in necrotizing fasciitis you may see gas in soft tissues from GAS necrotic process and also in gas gangrene - DO NOT use to diagnose as clinical suspicion followed by antibiotics should occur straight away as patient will be contagious (put in side room) with the potential to colonize others and potentially infect if IS is dampened
How should you treat viral skin and soft tissue infections?
Viruses: self-limiting but give Aciclovir if not for herpes, chickenpox and shingles
How should you treat bacterial skin and soft tissue infections?
Bacteria:
- Topical fuscidin for superficial infections e.g. impetigo
- S. Aureus is usually resistant e.g. MRSA so sampling and Flucoxacillin initially
- Streptococcus not normally resistant so penicillin
- Opportunistic e.g. diabetic ulcers often polymicrobial so sampling and Co-Amoxiclav initially
How should you treat fungal skin and soft tissue infections?
Usually superficial but rarely resistant to antimicrobials so topical Terbinafine often used which can be given orally if necessary
If you are unsure of the cause of a bacterial skin and soft tissue infection, what would you give as treatment?
Put the patient on IV and oral antibiotics e.g. Benzylpenicillin (IV) and Phenoxymethylpenicillin (oral)
When treating skin and soft tissue infections, what must you consider about the organism?
Is it a known organism +/- sensitivities and resistance profile?
OR
What is the most likely organism and their expected sensitivities/resistances?/
When treating skin and soft tissue infections, what must you consider about the patient?
Allergy/intolerance Renal/liver function Severity of infection or immunosuppression Risk of antibiotic-associated infection Route of administration Interactions w/ other medicines Age or ethnic group Pregnant/breast-feeding or taking oral contraception
When you have took into account the organism and patient, what can you then do?
Choose antibiotic, dose, route and duration (or consult guidelines)
