Skin infections Flashcards
What are the possible manifestations of S. aureus skin infection?
Impetigo Folliculitis Ecthyma Boil Carbuncle
What is impetigo?
Infection of subcorneal layer of epidermis.
Staphylococcal infection of the surface of the epidermis.
Honey-coloured, yellowish golden crust on eroded base.
Nose and mouth mainly affected, but can occur anywhere.
What is folliculitis?
Infection of mouth of hair follicle- can progress into boil.
What is ecthyma?
Infection of full thickness of epidermis.
Firmly adherent crust, on background erythema.
Surface of the skin is necrosing.
Commonly occurs after infected insect bites.
What is a boil?
Abscess of hair follicle.
What is a carbuncle?
Abscess of several adjacent hair follicles.
What is bullous impetigo?
Blister formation- superficial, easily broken, cause erosions.
S. aureus makes exfoliative toxin.
Causes cleavage of epidermis.
What is an abscess?
Might start off as an infected follicle which then expands.
Cavity formation with pus within it.
Best treatment is excision to let out pus.
What is staphylococcal scalded skin syndrome?
Caused by exfoliative toxin released into the bloodstream, has an effect on the skin distant to the site of the S. aureus infection.
Cleavage of epidermis, desquamating of epidermis.
Systemic .
Children < 5 years- immature immune system that can’t clear the toxin.
Erythema and desquamation (superficial).
Treat with antibiotics and emollients.
Does not affect mucous membranes, only skin.
What is treponema pallidum?
Gram negative spirochete. Cause of syphilis. Sexually transmitted disease. 12 million new cases per year worldwide. Increases transmission of HIV.
What percentage of GP consultations are skin related?
15%
What percentage of hospital outpatient attendances are skin related?
6%
What percentage of the population in Europe is referred to a dermatologist per year?
1%
What percentage of the population in Europe have a skin disease requiring medical intervention?
20%
What percentage of GP skin consultations in the UK are skin infections?
25%
What percentage of dermatologist consultations in the UK are skin infections?
5%
What conditions give rise to high rates of skin infections?
Hot, humid conditions and poor populations.
What is Staphylococcus aureus?
Gram positive coccus.
Bacteria have cell walls.
Produce toxins- exfoliative toxin, toxic shock toxin and enterotoxins.
What are the medical considerations that need to be made regarding Staphylococcus aureus?
Commensal- 30% of the population carry S. aureus, in the nostrils, on the skin under the arms or in the groin- asymptomatic.
Skin infections- significant proportion.
MRSA.
Toxin production.
Bone (osteomyelitis), joint (septic arthritis), lung infections (pneumonia).
Sepsis.
What toxins does Staphylococcus aureus produce?
Panton Valentine Leuocidin- virulence factor, necrotising infection).
Exfoliative toxin- blisters, cleavage of epidermis.
Toxic shock syndrome toxin 1 (TSST-1)- fever, malaise, hypotension, tachycardia seizures, rash, organ failure, related to tampons.
Enterotoxin- food handlers, diarrhoea and vomiting.
What are the features of the primary phase of syphilis infection?
At 3-8 weeks.
Painless ulcer (chancre) at inoculation site (genital or oral).
Lasts a few weeks, then heals.
What are the features of the secondary phase of syphilis infection?
At 6-12 weeks. Disseminated infection. Generalised widespread rash and lymphadenopathy. Flu-like illness. Lasts a few weeks, then gets better.
What are the features of tertiary syphilis infection?
Usually years later, without treatment.
Skin, neurological, and vascular manifestations (e.g. thoracic aneurysm- dilatation of thoracic aorta, causing aortic regurgitation, etc).
Bone lesions.
Gummatous skin lesions.
What are the features of congenital syphilis infection?
Acquired perinatally.
Early and late manifestations.
Placental transmission to baby from mother.
How can treponema pallidum spirochetes be identified in the laboratory?
Dark field microscopy of sample from a chancre.
What are the features of the rash of secondary syphilis?
Maculopapular, widespread.
Palms and soles involved.
What is condyloma lata?
Feature of secondary syphillis.
Warty lesions around perineum, axillae and groin.
What are some consequences of neurosyphilis?
Dementia Depression Psychoses Peripheral neuropathies Headaches
What are some consequences of congenital syphilis?
Miscarriage Still birth Prematurity Rashes Brain and neurological problems Bone disease
What is the site of latency of human herpes viruses?
Neuron.
What is the target cell of human herpes viruses?
Muco-epithelial.
What disease do HHV-1 and HHV-2 cause?
Oro-genital herpes.
Type 1- mostly oral.
Type 2- mostly genital.
a.k.a. herpes simplex viruses.
What disease does HHV-3 cause?
a.k.a. varicella zoster virus.
Chickenpox and shingles.
What are the possible clinical presentations of herpes simplex virus infection (HHV-1 and HHV-2)?
Vesicular rash- 2 weeks, vesicles on erythematous base, prodromal feeling of burning or stinging sensation.
Eczema herpeticum.
Herpes encephalitis.
First presentation may be with stomatitis: inflammation of the whole mouth.
How is varicella zoster virus (HHV-3) spread?
Inhalation or contact.
What is the incubation period of varicella zoster virus (HHV-3)?
About 12 days.
What are the signs and symptoms of varicella zoster virus (HHV-3) infection?
Feel unwell- sore throat, fever, malaise, headache, then break out in a rash about a day later.
Crops of vesicles on erythematous base- most concentrated on base, less on body and even less on arms and legs, involvement on the mouth but virtually none on hands and feet.
Vesicles progress into pustules, break down to form ulcers, then heal within about 2 weeks.
How can a person develop shingles?
Period of dormancy of varicella zoster virus (HHV-3) from previous chicken pox infection- lives in dorsal root ganglions of associated sensory cutaneous nerves, then can reactivate- shingles (herpes zoster) preceded by pain and stinging, dermatomal rash.
Can be bullous.
What is the treatment for shingles?
Acyclovir- get better over 2-3 weeks.
What are the different types of superficial skin fungal infections?
Dermatophytes (type of mould)
Yeasts
What are dermatophytes?
Type of mould (fungus), e.g. trichophyton rubrum.
Grow in keratin.
Long hyphae, grow from tip.
What are yeasts?
Fungus, e.g. candida.
Grow on warm wet surfaces.
Single cell and bud.
What causes tinea?
Dermatophytes.
What is tinea unguium?
Yellow, crumbly nail, can be quite destructive.
Caused by tinea (dermatophyte) fungus.
How is the diagnosis of tinea unguium dermatophyte infection confirmed?
Nail clippings sent to culture- 4-6 weeks.
How is tinea unguium dermatophyte infection treated?
3 month course of antifungal tablets- oral because current creams/topical agents can’t penetrate deep enough into nail or nail matrix to have activity against the fungal infection.
What is tinea capitis?
Dermatophyte infection of the scalp.
Children affected- adults have antifungal chemicals in sebum of their hair.
Diffusely scaly, or localised.
What is kerion?
Type of tinea capitis.
Localised.
Boggy mass, bit like an abscess.
Common error: not S. aureus in children, assume fungal until proved otherwise.
How is kerion (dermatophyte infection) diagnosed?
Take clippings/pluckings of hair, scrape the base of the lesion, and culture, result 4-6 weeks later, microscopy within 48 hours if there are fungal elements.
How is kerion (dermatophyte infection) treated?
Start on antifungal agent like terbinafine.
Fungus is too deep in the hair follicle for a cream/topical agent to work- give oral tablets.
What is tinea mannum?
Fungal infection on the hand.
Ringworm.
Round lesion with advancing edge.
What are the different types of tinea infection?
Tinea unguium (nails) Tinea capitis (scalp) Tinea mannum (hands) Tinea pedis (feet) Tinea cruris (groin) Tinea facei (face)
What is candida intertrigo and how is it treated?
Yeast.
Warm, moist environment.
Mouth, genital area, under breasts, axillae.
Intertrigo = wet, eczema-like fungal infection- inflammatory candida infection with satellites around it.
Treated with topical antifungal.
What is scabies (sarcoptes scabei)
Caused by a mite.
Human disease, spread by direct contact.
Crusted scabies- immunosuppressed patients, thousands of mites as opposed to around 20.
Patient picks up infection, female mite makes burrows just under the stratum corneum of the epidermis.
First 4 weeks or so, patient is asymptomatic.
Develop type 4 hypersensitivity reaction to mite and its faeces.
Develop very itchy erythematous rash.
Treat with insecticide cream,
What is a scabies burrow?
Typically, an infection will be 15-20 mites on the body.
Mites can be found by locating their burrows.
Burrows are about 0.5cm, with a black dot at one end (head of the mite), wiggly line.
What are the most common sites of burrows?
Axillae Groin Antecubital fossae Wrists Umbilicus Dorsum of the hands Insteps of the feet If these areas are clear of burrows, patient doesn’t have scabies
