Soft Tissue + Anaerobic Infections

NORMAL FLORA: gram +ve (Staph epidermidis, diphterioids, anaerobic cocci). The problem is in moist areas the fluctuation of normal flora varies --> this fluctuation produces an infection (usually). 

SUPERFICIAL ERYTHEMATOUS LESIONS

1.	Impetigo: infection within epidermis. Seen in children.
	Types/Cause: bullous - relatively rare (S. aureus), non-bullous (Group A B haemolytic Strep pyogenes)
	At risk: children, poor people, crowding etc
	Features: looks like a burn. Glomerulonephritis & RF are important complications (if Strep).	
	Dx: swab culture & serologe (look for DNAase - Strep)
	Rx: penicillin/flucoxcacillin

2.	Erysepilas: Quite rare nowadays.
	Cause: Group A Strep (also BCD to a lesser extent)
	Clinical feature: well demarcated raised reddened painful lesion

3.	Cellulitis: Infection involves deeper layers of dermis. 
	Cause: Major: Group A B haemolytic Strep pyogenes, Staph aureus. Minor: Aeromonas spp, Vibrio spp (Gram -ve), Haemophilus influenzae (children). 
	Clinical features: diffuse spreading infection, oedema, erythema, lymphadenopathy, fevers, chills. 
	

	Erysipeloid: meat & fish handlers. This is a specialised version of cellulitis. 
	Cause: Erisipelothrix Rheusiopathiae (gram +ve bacillus)
	At risk: fish & meat handlers
	
	Dx of Cellulitis / Erysepeloid: Clinically + biopsy --> culture
	Rx: Strep (penicillin), Staph aureus (flucoxacillin), anaerobes (metronidazole + debridement), haemophilus (cefotaxime). 

4.	Folliculitis: infection + inflammation of hair follicle 2nd to blockage
	Cause: Major: Staph aureus, Minor: perianal lesions (E. coli, Strep milleri) Pseudomonas aeruginosa is often the cause in patients who have hx of swimming in pools with low chlorine. 
	Clinical features: papules pierced by hair with surrounding erythema, pain, oedema.
	Special terms: stye (eyelash) + sycosois barbae (beard)
	
	If the folliculitis expands further it may become a furuncle (boils). Boils can rupture (pus drains) or can grow large and become multi-loculated abscesses called carbuncles. Pts at risk are: obese, immunocompromised, DM. 
	Complications: Pus can enter blood and go to organs --> abscesses
	Dx: asirate the pus --> culture
	Rx: Staph aureus (flucoxacillin), anaerobes (metronidazole), surgical clearance (if large). 

SINUS TRACTS

1.	Sinus tracts are a communication between deep tissue infectionos (abscesses) and the skin surface. A fistula is a communication between two epithelialised structures. You must take a swab from the deep infection if you require the accurate cause of the deep infection, because the sinus tract itself may contain numerous colonising organisms. Common culprit: Staph aureus. 
	
	Actinomycosis: "lumpy jaw". The swelling around the jaw tracts and drains 'sulphur granules' (clumps of microbes). The tract originates from a deep infection of the oral cavity. 
	Madura foot: Nocardia spp, & fungi. Organisms penetrate skin and form multiple abscesses deep (i.e.: osteomyelitis) and then drain onto the skin. 

WOUND INFECTIONS

1.	Simple post-operative wound infections: 
	Cause: Staph epidermidis & aureus, E. coli, Klebsiella spp, Enterbacter spp, Bacteroides spp, Clostridium spp. Review properties of each organisms at this stage. 
	Rx: flucox (Staph), cephalosporins/gentamicin (gram -ve), metronidazole (anaerobic). 

2.	Complicated Infections: These have a very high mortality rate (kill in hours) and are rapid spreading. Post surgery or post-trauma. 

	a) Synergistic bacterial gangrene (Melaney's gangrene): This often occurs after abdominal surgery or genital surgery (Fournier's gangrene - testes melt away). It involves the subcutaneous fat (hypodermis) + fascia of the muscles. DOES NOT INVOLVE MUSCLE. 
	Cause: Mixed (Staph aureus, Strep, gram -ve anaerobes)
	Dx: swab --> culture
	Rx: surgical excision of affected areas (amputations in limbs etc) + antibiotic therapy (Staph: flucoxacillin, Anaerobes: metronidazole).
	
	b) Gas gangrene: There is gas evident in the wound infection. Can extend to muscle --> clostridial myonecrosis.
	Cause: Major: Clostridium perfringens, Minor: Aeromonas spp, Klebsiella, Vibrio, E. coli, Bacteroides spp, anaerobic cocci. 

	c) Necrotizing fasciitis: Involves deep fascia + muscles --> extensive myonecrosis. 
	Cause: Group A B Strep pyogenes, Mixed: Clostridium spp, anaerobic cocci, Bacteroides spp
	Dx: aspirate --> gram stain --> aerobic / anaerobic culture. 
	Rx: surgical excision/debridement + antibiotics (i.e.: penicillin, metronidazole, clindamycin: penicillin allergic). 

	Acute pyomyositis: Rare infection in Australia. Very common in developing countries. Infects the muscle, voluminous pus. Cause: Staph aureus. Rx: surgical drainage + debridement. 

VENOUS ULCERS / BEDSORES

1.	These occur because there is an area of poorly supplied blood. This causes necrosis and infection settles. Cause: Gp A B haemolytic Strep pyogenes, Staph aureus. Occurs in bony prominences: ankle, sacrum (bed sores) etc. 

BURNS

1.	Common colonies are: Staph aureus, Strep pyogenes. Always treat the infection before putting a graft on.

BITES

1.	Dog / Cat: Pasteurella multicida (Gram -ve enterobacteriaceae), Rochalimaea henselae (cat scratch disease --> lymphadenitis). Check for rabies virus. 
	Rats: Streptobacillus mondiformis, Spirullum minor
	Dx: aspirate from depth of wound --> culture
	Rx: surgical debridement + antibiotics (tetracycline/erythromycin - cat scratch disease).