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Chapter: Medicine Study Notes : Skin

Bacterial infections of skin and soft tissue

Impetigo (School Sores) : Superficial infection involving the epidermis

Skin Infections


Bacterial infections of skin and soft tissue


Impetigo (School Sores)


·        = Superficial infection involving the epidermis

·        Most common in children during summer months

·        Non-bullous impetigo:

o  = Streptococcal impetigo 

o  Vesicles on erythematous base ® pustules (highly contagious) ® yellow-brown scabs (CRUSTY), associated with regional lymphadenopathy 

o  Ecthyma is deeper version – cut out edge 

o  Commonly result of skin break such as insect bites or chicken pox. Especially if overcrowding and warmer climates 

o  Goes for limbs and face

o  Fever uncommon.  Check lymph nodes 

o  Caused by Streptococcus Pyogenes with or without co-infection with Staphlococcus Aureus (can ® Scalded Skin Syndrome)

o  Commonest cause of post-strep glomerulonephritis

·        Bullous impetigo:

o  Due to Staph aureus of phage II (usually type 71)

o  Usually younger children 

o  Lesions: begin as vesicles – turn into flaccid bullae in response to toxins. Following rupture of the bullae, a moist red surface remains and varnish like crust appears


·        Neonatal Impetigo: Staph Aureus. Can spread to deeper tissues, umbilicus, bone and joints. If only one site, antiseptic bath once a day. If > 1 site then systemic antibiotics


·        Treatment:


o  To relieve symptoms, stop new lesions, prevent complications (e.g. cellulitis, acute glomerulonephritis), and stop spread to others

o  Flucloxacillin, dicloxacillin, a cephalosporin, erythromycin or clindamycin are all effective 

o  If MRSA: usually susceptible to co-trimoxazole (although not so good against S Pyogenes). Resistance to fusidic acid is also growing

o  Resistance is growing to topical agents (e.g. Mupirocin)


Scalded Skin Syndrome


·        Due to staph aureus toxin (may be distant site)

·        Skin peels off with little pressure – skin looks abnormal – damage from within

·        Commonest in infancy

·        Treatment: flucloxacillin plus burn treatment (including fluid balance)



·        Pyoderma located within the hair follicle

·        Usually caused by S aureus

·        Responds well to topical antibacterial measures




·        = A „boil‟

·        A deep inflammatory nodule

·        In skin areas subject to friction and perspiration and containing hair follicles

·        Often drain spontaneously, especially with moist heat 

·        If recurrent, then ?nasal carriage of S aureus. Treat with topical intranasal mupirocin or systemic rifampicin 

·        May progress to a carbuncle: more extensive involving subcutaneous fat. If surrounding cellulitis or if on face then need iv antibiotics


Cellulitis and Erysipelas


·        Infection of subcutaneous layer by Strep Pyogenes

·        Symptoms: inflammation, warmth, erythema, pain, fever 

·        Can ® sepsis, bullae and small abscesses

·        Also erythema around anus with puss and blood in stool

·        May desquamate

·        Impaired lymphatic drainage predisposes to recurrent cellulitis (e.g. pelvic, joint, breast surgery) 

·        Erysipelas is a distinctive superficial cellulitis, primarily involves dermis. Raised and well demarcated. Prominent lymphatic involvement. May ® chills, fever and malaise

·        Treatment: S Pyogenes still very susceptible to penicillin


Diabetic Foot infections


·        Due to neuropathy, ischaemia, and infection

·        Causes: often S aureus, also coagulase negative staphylococci and streptococci

·        Often nasal carriage of S aureus

·        Treatment: anti-staphylococcal agents.  IV treatment if deep tissues or bone involvement


Deep Tissue Infections


·        Necrotising Fasciitis: See Streptococcus Pyogenes (Group A, b Haemolytic)

·        Superficial necrotising cellulitis or streptococcal gangrene (rare) 

·        Gas Gangrene (Clostridial myonecrosis): rapidly progressive and life threatening infection of muscle due to Clostridium Perfringens


Scarlet Fever



·        NB: Lancefield Groups only apply to b Haemolytic Streps

·        Causes:

o   Commonly: acute pharyngitis, cellulitis, impetigo (also caused by group C)


o   Uncommonly: necrotising fasciitis (haemolytic strep gangrene), strep toxic shock syndrome, scarlet fever, erysipelas (= contagious skin infection with strep pyogenes), acute otitis media

o   Rarely: pneumonia, infective endocarditis

·        Has remained sensitive to penicillin

·        Identical strep can lead to a variety of infections:

o   Sore throat

o   Impetigo/Cellulitis.

o   Toxic Shock Syndrome

o   Myositis

o   Necrotising Fasciitis

·        Infection via throat (mainly) or via skin (impetigo/wound infection):

o   Suppurative: tissue invasion

o   Non-suppurative (after 2 – 8 weeks):

§  Rheumatic Fever

§  Glomerulonephritis

o   Super antigens: pyogenic exotoxins – ability to avoid classical antigen processing by APCs




·        May require drainage.  Distinguish from lymphadenopathy

·        Usually Staph aureus, also TB

·        See Cervical Lumps


Toxic Shock Syndrome

·        Desquamation a week later characteristic


Dog Bites


·        Clean carefully (may need local anaesthetic) 

·        Treat with broad-spectrum antibiotic. Amoxycillin/clavulanate. NNT = 14. So limit to high risk of infection only. Consider anaerobe cover (eg metronidazole)

·        Screen for post-traumatic stress disorder afterwards

·        Report the dog


Lyme Disease


·        Tick borne spirochete (Borrelia burgdorferi)

·        Gives erythema migrans, headache, fever, myalgia, fatigue

·        Leads later to widespread systemic manifestations

·        Discovered in Connecticut, USA.  No in NZ


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