Skin and Soft Tissue Infections Flashcards
Describe cellulitis and the most common causative organisms.
Bacteria breach the skin barrier and infect and spread throughout the deeper dermis and fat
- characterised by oedema, erythema and warmth
- most common in the lower extremities
- S.aureus, beta-haemolytic streptocci (A, B, C and G)
Which group of people are most likely to get cellulitis?
Middle aged and elderly people
Where does S.aureus normally live?
Carried by 30-40% of normal people, in the nose or moist areas of the skin
Type carried is stable
2% MRSA prevalence
What and where is the average carriage of strep pyogenes?
5-15% carriage
Normally in the respiratory tract and vaginal tract
What are the non-modifiable risk factors for cellulitis?
Pregnancy White caucasian Trauma Animal/insect bites Tattoos
What are the modifiable risk factors for cellulitis?
Venous insufficiency Lymphoedema Ulcers Eczema Athletes foot Burns Surgery
What factors are incorporated when considering the management decisions in SSTI?
Severity
Anatomical site
Health Care Associate Infections
Co-morbidities
When deciding between treating at home or treating in the community, what criteria mean they have to remain in hospital?
Severe, localising pain Confusion Rapidly evolving skin lesions or skin blistering Systolic blood pressure <100mmHg Sepsis syndrome - heart rate >100 - RR >20/min - temp >38 or <36 - WCC >12 or <4/mm3
Describe a class 1 soft tissue/skin infection.
No sign of systemic toxicity
No co-morbidities
Oral antibiotics
Treated as an outpatient
Describe a class 2 soft tissue/skin infection.
May have a systemic illness
Has PVD, obesity or venous insufficiency
IV antibiotics
Hospital treatment for at least 48 hours, then community treatment
Describe a class 3 soft tissue/skin infection.
Significant systemic illness
Unstable co-morbidities
IV antibiotics
Hospital treatment
Describe a class 4 soft tissue/skin infection.
Sepsis syndrome/necrotising fasciitis
Unstable co-morbidities
IV antibiotics and surgery
Hospital treatment
What is the organism and associated treatment for typical cellulitis?
S.pyogenes
- ampicillin or flucloxacillin
What is the organism and associated treatment for typical cellulitis with pus?
S.aureus (sometimes MRSA)
- Flucloxacillin
- Vancomycin
What is the treatment for typical cellulitis when the patient has a penicillin allergy?
Doxycycline
Clindamycin
or
Vancomycin
What is the organism and associated treatment for cellulitis caused by cat/dog bite?
Pasteurella multocida
- co-amoxiclav
- doxycycline and
- metronidazole
What is the organism and associated treatment for cellulitis after fresh water exposure?
Aeromonas hydrophila
- ciprofloxacin
What is the organism and associated treatment for cellulitis after salt water exposure?
Vibrio vulnificus
- doxycycline
What is the organism and associated treatment for necrotising fasciitis?
C.perfringes/S.pyogenes
- flucloxacillin, clindamycin, gentamicin and metronidazole
What is the organism and associated treatment for cellulitis in butchers/fish handlers?
Erysipelothrix
- ciprofloaxacin
What are the differential diagnoses for cellulitis?
Stasis dermatitis - bilateral, circumfernetial
Acute arthritis - joint involvement
Pyoderma gangrenosum - ulceration on legs
Hypersensitivity - exposure to allergens, no fever or pain
DVT - no skin changes or fever
Necrotising fasciitis - severe pain, swelling, fever, rapid progression
What things should you consider when someone with cellulitis isn’t improving after treatment?
Resistance
Admission to hospital
Underlying conditions (bone infection, abscess, PVD)
Incorrect diagnosis (DVT, abscess, chronic changes)
What is the difference between cellulitis and erysipelas?
Cellulitis - bacterial infection of the lower layers of the skin
Erysipelas - bacterial infection of the upper layers of the skin, and superficial lymphatics
- raised lesion with clear line of demarcation
Describe what parts of the body erysipelas involves
Classically butterfly involvement of the face (20% of cases)
Legs are affected (80% of cases)
Can also involve the ear
What are the most common causative organisms of erysipelas?
Group A strep
- more rarely you can get B, C and G as well
- staph aureus also a rare cause
How is erysipelas diagnosed?
Elevated ASOT for 10 days
Mainly a clinical diagnosis, based on how the skin looks
Describe the appearance of an impetigo skin infection.
Sores and blisters, commonly in a perioral location
- honey coloured
What causes an impetigo skin infection?
Highly transmissible staphylococcus infection of the epidermis
Who would an impetigo infection most commonly affect?
Children
Sports people
What is the treatment for an impetigo skin infection?
Gently remove the crust
Treat with flucloxacillin
- be aware of the risk of a secondary infection (e.g. HSV)
What is the definition of necrotising fasciitis?
Severe inflammation of the muscle sheath that leads to necrosis of the subcutaneous tissue and adjacent fascia
What bacteria (and virulence factors) cause necrotising fasciitis?
Most commonly a mixed infection (aerobes and anaerobes)
Toxin mediated - superantigens and cytokine release
What are the important differentiating factors between cellulitis and necrotising fasciitis?
Initial pain becomes painless Rapid spread Systematically unwell Dusky skin and necrosis May have skin crepitus
What are the clinical manifestations of necrotising fasciitis?
Rapid progression
Most common on the extremities
Initially erythema and swelling without shapr margins
Pain and tenderness
Lymphatic involvement is rare
Colour change from red-purple to blue-grey
Skin breakdown and bullae with development of anaethesia
Probing of the lesion reveals easy through the tissues
Describe the management of necrotising fasciits.
Surgical debridement
Antibiotics
Activated protein C (evidence is limited and can’t b used within 24 hours of surgery)
Which antibiotics are used in the management of necrotising fasciitis?
Penicillin Flucloxacillin Clindamycin Gentamicin Metronidazole
When is prophylactic treatment for bites needed?
If the bite is deep, on the hands or the patient is immunocompromised/ splenectomised
What is the treatment for a bite?
Gram stain of the wound and blood cultures
Debridement and abscess drainage
Antibiotics
- cover staph, anaerobes, pasteurella and capnocytophaga
Rabies immunoglobulin and vaccination is appropriate
Describe pasteurella and it’s associated treatments.
Gram negative bacteria Most common pathogen which infects bites Treated with - penicillins - cephalosporins - tetracyclines - quinolones - macrolides Co-amoxiclav, doxycycline and metronidazole
Aeromonas species are associated with what clinical syndrome?
- caught after exposure to fresh water
Rapidly developing infection with fever and sepsis
Edwardsiella tarda are associated with what clinical syndrome?
- caught after exposure to fresh water
Cellulitis, occasionally fulminant infection with bacterameia
Erysipelothrix rhusiopathiae are associated with what clinical syndrome?
- caught after puncture wounds from crabs
Indolent localised cutaneous eruption, erysipeloid
Vibrio vulnificus are associated with what clinical syndrome?
- caught after exposure to salt or brackish water
Rapidly progressive necrotising infection, bullous, cellulitis, sepsis
Mycobacterium marinum are associated with what clinical syndrome?
- caight after exposure to fresh or salt water
Indolent infection, papules to ulcers, ascending lesion may resemble sporotrichosis
What is tinea?
A superficial dermatophyte infections characterised by scaly, inflammatory or non-inflammatory patches
- generally limited to the epidermis and expands in a centrifungal pattern
What is classification of tinea based off?
The affect region
- tinea pedis for feet (athletes foot)
- tinea corporis for the body
- tinea capitis for head/scalp
- tinea curis for groin (jock itch)
What is tinea caused by?
Dermatophytes
- trichophyton (most common)
- microsporum
- epidermophyton
How is a tinae infection diagnosed?
Potassium hydroxide (KOH) preparation from a skin scraping
How is erythema infectiosum caused?
Parvovirus B19
- transmission via respiratory droplets, blood or blood products
What are the symptoms of erythema infectiosum?
Fever
Headache
Runny nose
Pruritic rash on the face (slapped cheek), torso and extremities
What are the complications of persistent erythema infectiosum?
Persistent arthropathy Gloves-and-socks syndrome Papular, purpuric eruptions on the hands and feet Acute cessation of RBC production - transient aplastic crisis - chronic RBC aplasia - hydrops fetalis - congenital anaemia
What is hand-foot-and-mouth disease?
A viral illness with oral and sital-extremitry lesions
What is the cause of hand-and-foot-and-mouth disease?
Coxsackie virus A16
- typically affects children and infants
How can hand-foot-and-mouth disease cause and epidemic?
Highly contagious during the first week of the illness
- direct contact with nasal and oral secretions or faecal material
What are the symptoms of hand-foot-and-mouth disease?
Fever Rash Headache Sore throat Oropharyngeal ulcers Loss of appetite
How can herpes reoccur once it has been treated?
Virus doesn’t disappear from the body, lives latent in the sensory never ganglia
What is the diagnosis and treatment for herpes simplex?
Clinical diagnosis - blood or vesicle fluid for PCR - serology - be careful as 60% of cases are asymptomatic Treatment - acyclovir (topical, oral or IV)
What two conditions can the varicella zoster virsu cause?
Chickenpox
Shingles
How is chicken pox diagnosed?
PCR of vesicle fluid (or serology)
Chickenpox is self-limiting in children; how is it problematic in adults?
Can cause congenital abnormalities during pregnany
Pneumonitis
If an at risk adult (pregnant, immunocompromised or has contracted penumonitis) contracts chickenpox, how are they treated?
Need to be treated within 48 hours of symptoms
- acyclovir PO/IV
Describe shingles.
Reactivation of dormant VZV (dorsal root ganglia)
Dermatomal distribution
Highly contagious until all the vesicles have crusted over
How is shingles treated?
Only the immunocompromised patients and those with disseminated infection are treated
- acyclovir
NSAIDs and gabapneitn for the pain
Briefly describe burns.
Damage to the skin (Heat, chemical, radiation, cold) causing protein denaturing
What conditions can occur because a burn has compromised resistance to the environment?
Infection - must be diagnosed clinically (burn swabs are rarely sterile)
Hypothermia
Acid-base abnormalities
Dehydration
How are burns managed?
Dressings Topical antimicrobials (e.g. sulfadiazine, may delay re-epithelialisation) Topical antibiotics (bacitracin) Systemic antibiotics (directed by culture results) are required in invasive infection
What is staphylococcal scalded skin syndrome, and what are its symptoms?
Staph aureus strains producing an exfoliative exotoxin
Widespread bullae formation and exfoliation
- known as Ritter’s disease or Pehmphigus neonatorum in the neonate
Symptoms are fever, tenderness and a scarlatiniform rash
What is the causative pathogen and virulence factors for Scarlet fever?
Infections with a streptococcal strain that elaborates streptococcal exotoxins or erythrogenic toxins
- usually post-pharyngitis but may complicate wound infections and post-partum infections
Describe the signs and symptoms of Scarlet fever.
Diffuse red blush (2nd day of infection)
- becomes a deeper red blanch on pressure
- starts on upper chest and spreads to trunk, neck and extremities
Mild eosinophilia
Occlusion of sweat glands (skin feel like sandpaper)
Palms, soles and face are normally spared
Circum-oral pallor
White strawberry tongue followed by red strawberry tongue
High fever and systemic toxicity is severe cases
What are the major features of cutaneous anthrax?
Surrounded by extensive oedema
Painless and non-tender
What are the minor features of cutaneous anthrax?
Development of black eschar
Progresses over 2-6 days through papular, vesicular and ulcerated stages before eschar appears
- hands, forearm, face and neck are most common
Discharge of serous fluid
Local erythema and induration
Local lymphadenopathy
Systemical malaise (headache, chills and sore throat -> afebrile)
What are the specific risk factors for cutaneous anthrax?
Working with animals or animal hides
Making, owning or playing an animal hide drum
Drug use (particularly heroin)
Travel
Working in postal sorting office or handling large volumes of mail
Received threatening letter or package containing white powder
What are the antibiotics used for cutaneous anthrax treatment?
Penicillin Flucloxacillin Clindamycin Ciprofloxacin Metronidazole
Describe PVL producing Staph aureus.
PVL is a toxin which destroys white blood cells
Carried by less than 2% of S.aureus isolates (normally MSSA)
Community isolates are more likely to carry the toxin that hospital
What conditions are associated with PVL producing S.aureus?
Necrotising fasciitis
Pyogenic skin infections
Septic arthritis
Fulminant pneumonia
When should PVL producing S.aureus be suspected?
Recurrent/multiple boils
- especially those in close contact situations
What is the diagnosis and management plan for PVL producing S.aureus?
Screen nose, throat, axilla, perineum and skin lesions for carriage
PCR for toxin gene
Drainage and treatment according to sensitivity patterns
Decolonise using standard MRSA regimens
