skin infections Flashcards
skin infections: summarise the epidemiology of organisms that commonly cause skin infections, and recall the biology and main clinical features of common skin infections and infestations, including Staphylococcus aureus, Treponema pallidum, herpes simplex, varicella zoster, Trichophytum rubrum and Sarcoptes scabei
epidemiology of skin disease
skin disease common, with skin high infection rates in hot humid conditions and poor populations
skin disease due to infection in GP vs hospital
more infection % in GP than hospitals
prevalence of skin infection by geographical infection
malignant tumours higher in white areas; bacterial, fungal, eczema/dermatitis higher in developing countries
describe appearance of Staph. aureus
“bundles of grapes” with a capsule
commensal Staph. aureus location (but can become skin infection)
nose, armpits and groin
resistant Staph. aureus
MRSA (not worse just harder to treat)
4 toxins produced by Staph. aureus and what they cause
panton valentine leucocidin (aggressive soft tissue infection), exfoliative toxin (blisters), TSST-1 (septicaemic features), enterotoxin (causes diarrhoea from contamination of food)
besides skin infection, what else can it infect (can go on and cause sepsis)
bone, joint and lung (lung particularly after flu)
infection of Staph. aureus in subcorneal layer of epidermis
impetigo (honey-coloured crustic erosion; can produce exfoliative toxin causing splitting of skin to form bullous - blisters containing bacteria which cause puss)
infection of Staph. aureus of mouth of hair follicle
folliculitits
infection of Staph. aureus of full thickness of epidermis
ecythma (crusted thick lesion with necrotic surface of skin, forming thick scar; caused by infected insect bite)
infection of Staph. aureus causing abscess of puss of hair follicle
boil (same as abscess)
infection of Staph. aureus causing multiple abscesses of several adjacent hair follicle
carbuncle
who is affected by staphylococccal scalded skin syndrome
children under 5 (Staph. aureus causing superficial cleavage of skin)
how is staphylococccal scalded skin syndrome treated
antibiotics
key features of Staph. auereus
variety of presentations, golden crust, diagnosed by swab, determine which antibiotics it will respond to
what is Treponema pallidum
spiral gram -ve bacteria causing syphilis (STD)
3 phases of syphilis
primary, secondary, latent syphilis, tertiary syphilis
describe primary stage of syphilis
3-8 weeks after inoculation, causing painless ulcer (weepy ulcer on genitals or mouth)
describe secondary stage of syphilis
6-12 weeks after inoculation, disseminated infection, generalised rash and lymphadenopathy. with ondyloma lata “warty” regions present too
describe tertiary stage of syphilis
years later, causing inflammatory lesions affecting skin, neurological and vascular (can also cause thoracic aneurysms)
describe congenital syphilis
acquired perinatally with early and late manifestations
what can neurosyphilis cause
dementia
pregnancy risks of congenital syphilis
miscarriage, still birth, prematurity, rashes, brain and neurological problems, bone disease
diagnosis of primary syphilis
swab, blood test (may or may not be positive)
diagnosis of secondary and later syphilis
serology positive; can be made by rash and biopsy (plasma cells present)
treatment of syphilis
antibiotics
3 members of human herpes virus family ( with latency site of neurones (can reactivate)
HSV-1 (affects around mouth), HSV-2 (affects around genitals), VZV (causes chickenpox and shingles)
presentation of herpes simplex (HSV-1 and 2)
vesicular rash (present on mouth, genitals or anywhere else but heal after 2 weeks; with HSV-2 can form crusty blisters); at stress/illness can reactivate
eczema risk and what herpes infection causes in patients with eczema
defective barrier function so susceptible to skin infection (with herpes, causes eczema herpeticum)
diagnosis of herpes simplex
clinical, swab for PCR
treatment of herpes simplex
acyclovir
VZV (herpes varicella zoster, chickenpox or shingles) virus incubation
incubation after 1 week: malaise, fever, sore throat, lethargic -> rash with groups of vesicles on erythematous base, concentrated centripetally (face and trunk)
complications of VZV
encephalitis (inflammation of brain), pneumonia in elderly
describe reactivation of latent VZV
latent in dorsal root ganglion but reactivates in stress/illness (only down one dermatome)
symptoms of VZV if effects V1 nerve
facial VZV, causing pain and potentially causing blindness
vaccine for chickenpox and shingles
no vaccine for children with chickenpox, vaccine for elderly with shingles
2 types of superficial skin fungal infections
dermatophytes (mould), yeasts
where are dermatophytes present
grows in keratin so affects skin, hair and nails
where are yeast (e.g. candida) present
grow on warm, wet surfaces in body folds
what happens to nails in Tinea unguium (dermatophyte)
become yellow and crumbly
who are affected by Tinea capitis (dermatophyte)
affect prepubertal children
presentation of Tinea capitis (dermatophyte)
crusty lesion on scalp or kerion (boggy mass with pustules) - affects Afrocaribbean children more
location of Tinea manuum
affects hands
location of Tinea pedis
affects toes
location of Tinea cruris
affects skin of inner thigh
location of Tinea facei
affects face
how can Tinea dermatophytes be transmitted
via pets
candida presentation
red, sore, spotty
diagnosis of superficial skin fungal infections
scrapings of rash, clippings of nail or pluckings of hair -> cultured/PCR
treatment of dermatophytes
terbinafine (cream if skin, tablets if not)
treatment of candida
antifungal cream
what causes scabies
mites (female burrows into stratum cornea and lays eggs)
diagnosis of scabies
look for burrow (4mm long squiggle with black dot (head of mite) at one end)
common sites of scabies burrows
finger webs, toe webs, genital area (inflammatory lumps), axilla
describe reaction to scabies mites
initial infection is asymptomatic, but after 4 weeks develop immune reaction to cause widespread eczema
treatment for scabies
insecticide cream
transmission of scabies
direct contact for many minutes
consequences of secondary bacterial infections following chronic scabies
cause renal failure due to skin infections of Streptococcus
