Derm - Infections + Infestations Flashcards
What is staphylococcus aureus and how does it infect the skin?
bacterium that has many virulence factors, e.g. receptord that allow it to bind to fibrin
fibrin is in abundance on wound surfaces etc.
What can Staph infections result in?
→ ecthyma (deep dermis skin infetion where ulcers form under crusted sores)
→ impetigo (superficial skin infection)
→ cellulitis
→ folliculitis
→ furunculosis (deep infection of the hair follicle leading to abscess formation)
→ carbuncles (cluster of boils — painful, pus-filled bumps)
→ SSSS (staphylococcal scalded skin syndrome)
→ superinfects other dermatoses (e.g. atopic eczema, HSV, leg ulcers)
How does streptococcus cause skin infections?
→ virulence factors that allow it to attach to the epithelial surfaces via the lipoteichoic acid portion of fimbriae
→ has M protein (anti-phagocytic) + hyaluronic acid capsule
→ produces erythrogenic exotoxins
→ produces streptolysins S and O
What can a Stretococcus infection result in?
→ ecthyma
→ cellulitis
→ impetigo
→ erysipelas (an infection of the upper layers of the skin +
→ scarlet fever
→ necrotizing fascitis
→ superinfects other dermatsoses (e.g. leg ulcers)
What is folliculitis?
→ folliculitis
→ follicular erythema, sometimes pustular
→ maybe non-infectious or infectious
What kind of folliculitis is associated with HIV?
eosinophillic (non-infectious) folliculitis
What can give you recurrent folliculitis?
nasal carriage of staphylococcus aureus, especially strains expressing Panton-Valentine leukocidin (PVL)
How is folliculitis treated?
→ antibiotics (usually flucloxacillin or erythromycin) (depends after a swab)
→ incision + drainage is required for furunculosis
What is the difference between a furuncle + carbuncle?
→ furuncle = deep follicular abscess
→ carbuncle = deep follicular abcess that involves adjacent connected follicles
→ carbuncle more likely to lead to complications such as cellulitis + septicaemia
What is this?
furuncle
What is this?
carbuncle
Why do some patients develop recurrent staphylococcal impetigo or recurrent furunculosis?
• Establishment as a part of the resident microbial flora :
- Abundant in nasal flora
•Immune deficiency :
- Hypogammaglobulinaemia
- HyperIgE syndrome – deficiency - Chronic granulomatous disease
- AIDS
- Diabetes Mellitus
What is PVL?
→ Panton-Valentine Leukocidin
→ β-pore-forming exotoxin
What does PVL allow staphylococcus aureus to do?
→ Leukocyte destruction and tissue necrosis
→ Higher morbidity, mortality and transmissibility
How does PVL staph. aureus manifest in the skin?
→ recurrent + painful abcesses
→ folliculitis
→ cellulitis
→ often in more than one site, recurrent + present in contacts
How does PVL staph. aureus manifest extracutaneously?
→ necrotising pneumonia
→ necrotising fascitis
→ purpura fulminans
What are the 5 risks or ways in which PVL staph. aureus can be acquired?
Close contact (hugging, contact sports)
Contaminted items (gym equipment, towels, razors)
Crowding (crowded living conditions)
Cleanliness of environement (unclean = more risk)
Cuts + grazes (allows bacteria to enter the body)
What is the treatement protocol for PVL staph. aureus infection?
→ consult local microbiologist
→ antibiotics (usually tetracycline)
→ decolonisation (e.g. chlorhexidine body wash for 7 days or nasal application of mupirocin ointment, 5 days)
→ treatment of close contacts
What is pseudomonal folliculitis?
an infection of the hair follicle with Pseudomonas bacteria
What causes pseudomonal folliculitis?
associated with hot tub use, swimming pools, depilatories + wet suits
How does pseudomonal folliculitis progress?
appears 1-3 days after exposure, as a diffuse truncal eruption or follicular erythmatous papule
rarely can progress to abcesses, lymphangitis + fever
How is pseudomonal folliculitis treated?
most cases self-limited, no treatement required
severe or recurrent cases can be treated with oral ciprofloxacin
What is this?
cellulitis - infections of lower dermis + subcutaneous tissue
What is the main symptom of cellulitis?
tender swelling with ill-defined blanching erythema or oedema
What causes cellulitis?
→ streptococcus pyogenes
→ staphylococcus aureus
What is a pre-disposing factor for cellulitis?
oedema
What is the treatment for cellulitis?
systemic antibiotics
What is this?
impetigo
What is impetigo?
Superficial bacterial infection, stuck-on, honey-coloured crusts overlying an erosion, often affects face (perioral, ears, nasal)
What can cause impetigo?
streptococci (non-bullous or non-blistering)
staphylococci (bullous or blistering)
How do you tell the difference between staph + strep impetigo?
strep = non-blistering or non-bullous
staph = bullous or blistering
Why does staph cause blistering or bullous in impetigo?
Caused by exfoliative toxins A & B, split epidermis by targeting desmoglein I
How is impetigo treated?
topical +/- systemic antibiotics
What is impetiginastion?
superficial impetigo in the context of atopic dermatitis
caused by staph
characteristic gold crust
What is this?
impetiginisation
What is ecthyma?
severe form of streptococcal impetigo
thich crust overlying a punch out ulceration surrounded by erythema
usually on lower extremities
What is SSSS?
staphylococcal scalded skin syndrome
Who usually gets SSSS?
neonates, infants, immunocompromised adults
What causes SSSS?
the exfoliative toxins of staph
Why can’t the staph organism be cultured from the scalded skin in SSSS?
infection occurs at a distant site from the SSSS
Why does SSSS often manifest in neonates, infants or immunocompromised adults?
→ kidneys cannot excrete the exfoliative toxin quickly
→ Diffuse tender erythema that rapidly progresses to flaccid bullae
→ Wrinkle and exfoliate, leaving oozing erythematous base
What can SSSS clinically resemble?
Stevens-Johnson syndrome / toxic epidermal necrolysis
What is Toxic Shock Syndrome?
febrile illness due to group A staph. aureus strain that produces pyrogenic exotoxin TSST-1
What are the symptoms + signs of Toxic Shock Syndrome?
- fever > 38.9
- Hypotension
- Diffuse erythema
- Involvement of ≥ systems:
– Gastrointestinal
– Muscular
– CNS
- Renal
- Hepatic
- Mucous membranes (erythema)
- Hematologic (platelets <100 000/mm3)
- Desquamation predominantly of palms and soles 1-2 weeks after resolution of erythema
What is this?
toxic shock syndrome
What is erythrasma?
infection of Corynebacterium minutissimum
What are the symptoms + signs of erythrasma?
well demarcated patches in intertriginous areas
intially pink
become brown + scaly
What is this?
erythrasma
What is pitted keratolysis?
pitted erosions of soles
What is pitted keratolysis caused by?
corynebacteria
What is the treatment for pitted keratolysis?
topical clindamycin
What is erysipeloid?
erythema + oedema of the hand after handling contaminated raw fish or meat
extends slowly over weeks
What bacteria causes erysipeloid?
erysipelothrix rhusiopathiae
What is this?
erysipeloid
What is anthrax?
Painless necrotic ulcer with surrounding oedema and regional lymphadenopathy (with pain in lymph nodes) at the site of contact with hides, bone meal or wool infected with Bacillus anthracis
What causes anthrax?
Bacillus anthracis
What is this?
anthrax
What is blistering distal dactylitis?
Rare infection
Typically - young children
1 or more tender superficial bullae on erythematous base on the volar fat pad of a finger
Toes may rarely be affected
What can cause blistering distal dactylitis?
streptococcus pyogenes and staphylococcus aureus
What is this?
blisteirng distal dactylitis
What is erysipelas?
infection of deep demris + subcutis
What causes erysipelas?
β-haemolytic streptococci or Staphylococcus aureus
What are the symptoms + signs of erysipelas?
Painful
Prodrome of malaise, fever, headache.
Presents as erythematous indurated plaque with a sharply demarcated border and a cliff-drop edge (+/- blistering)
Face or limb (+/- red streak of lymphangitis and local lymphadenopathy)
Portal of entry must be sought (e.g. tinea pedis).
Systemic symptoms (fever, malaise).
What is the treatment for erysipelas?
Treated with intravenous antibiotics
What is scarlet fever?
bacterial illness that develops in some people who have strep throat
primarily a disease of children
What is scarlet fever caused by?
Caused by upper respiratory tract infection with erythrogenic toxin-producing Streptococcus pyogenes
What are the symptoms + progression of scarlet fever?
- Preceded by sore throat, headache, malaise, chills, anorexia and fever
- Eruption begins 12-48 hours later
- Blanchable tiny pinkish-red spots on chest, neck and axillae
- Spread to whole body within 12 hours
- Sandpaper-like texture
What are some complications of scarlet fever?
otitis, mastoiditis, sinusitis, pneumonia, myocarditis, hepatitis, meningitis, rheumatic fever, acute glomerulonephritis
What is this?
scarlet fever
What is necrotising fasciitis?
Initial dusky induration (usually of a limb), followed by rapid painful necrosis of skin, connective tissue and muscle
What causes necrotising fasciitis?
streptococci
staphylococci
enterobacteria
anaerobes
What is the mortality of necrotising faciitis?
potentially fatal
high mortality
What is the diagnostic procedure for necrotising fasciitis?
- Prompt diagnosis essential (requires high index of suspicion)
- MRI can aid diagnosis.
- Blood and tissue cultures can determine organisms and sensitivities.
How is necrotising fasciitis treated?
broad-spectrum parenteral antibiotics and surgical debridement
What is atypical mycobacterial infection?
important cause of infection in immunosupressed states
What can cause atypical mycobacterial infection?
mycobacterium marinum
mycobacterium chelonae
mycobacterium ulcerans
What type of infection does mycobacterium marinum cause?
indolent granulomatous ulcers (fish-tank granuloma) in healthy people (Sporotrichoid spread)