Cause:Streptococcus pyogenes, group A, ß-hemolytic or other types strep
Pathophys:
Erysipelas is mainly in lymphatics
Cellulitis, in subcutaneous tissues
NF, infections dissect along fascial planes, so skin is last to go, and look deceptively benign; 1/3 of the time NF is associated with anaerobic bacteria as well
Impetigo is a superficial skin infection, starts in a break in the skin
Erysipelas and cellulitis, common; necrotizing fasciitis (NF), rare, 1/yr in big hospital. Invasive strep infections in 1.5/100 000/yr in general population, 3/1000 of household contacts (Nejm 1996;335:547); but invasive cases are just the tip of the iceberg since same strain will be found causing much more pharyngitis in the community (Jama 1997;277:38)
Sx:Pain, fever, and rapid spreading in erysipelas, cellulitis, and NF; in impetigo, sx are of a weeping rash usually in a child
Si:
Erysipelas has sharp limits, symmetric swelling, usually across bridge of nose
Cellulitis has little edema and indistinct limits; may be perianal in children
NF has edema, fever, redness, gas crepitation (in 50%), anesthesia (nerve infarction), ecchymosis (thrombosis)
In impetigo, rash has bullae with honey yellow exudate
Toxic shock syndrome (Toxic Shock Syndrome) and acute glomerular nephritis can occur with all
Erysipelas: r/o ERYSIPELOID(hands, exposure to raw meat and animals, slower spread; gram-positive rod, culture skin biopsy; rx with penicillin, etc)
Cellulitis: erythema nodosum and endocarditis, r/o acute axillary lymphadenitis (Nejm 1990;323:655), vibrio saltwater infections, pasturella from animal bites, pseudomonas in diabetic feet, mouth anaerobes from human bites, aeromonas cellulitisfrom leeches or freshwater abrasions rx'd w cipro or imipenem/cilastin
NF: r/o gas gangrene
Lab:
Bact:In all, culture, and gram-positive cocci in chains on Gram stain
Path:For NF, frozen section biopsy
Serol:ASO titers elevated
Rx:
Prevention w bacitracin dressing no better than vaseline (Jama 1996;276:972)
for all, antibiotics like penicillin, erythromycin although 20-40% resistance now in Finland (Nejm 1992;326:292)
of impetigo, mupirocin (Bactroban) ointment (not cream) topically tid as good as po antibiotics; $10/15-gm tube (Med Let 1988;30:55); debated if need to cover for resistant staph, esp nonbullous type (Lancet 1991;338:803)
of NF, extensive surgical debridement 1st; clindamycin helps decr toxin production