Bacterial and Parasitic Infections of Skin

Question 1

Impeticgo: general presentation, etiology, diagnosis

Answer 1

General: Yellow crusted skin lesions (near nostrils and spread across face and appear on trunk and limbs); more common in children, very contagious, some cases with severe bullae;
Etiology: usually mix of strep and staph (30% of pop is Staph aureus carrier), carriers, maybe carriers suffer periodic infections, or infect others by contact or fomites
Diagnosis: clinically and history; smears from pus may show Gram + cocci in clumps or chains (gram+ either coagulase-positive, beta hemolytic, DNAse-positive, salt resistant vs. coag-negative, beta hemolytic, bacitrain-sens, reactive with Group A strep antiserum; bullous impetigo would be S aureus due to EXFOLIATIN)

Question 2

Treatment and Prevention of Impetigo:

Answer 2

Treat: keep area clean and dry; for MILD: mupirocin ointment topically (OTC antibiotic creams less likely to be effective); for SEVERE: penicillinase-resistant penicillins, or amoxicillin with penicillinase-inhibior, or cephalosporins; for EXTENSIVE OR DRUG-RESISTANT: sens test and prescribe appropriately, unlikely to need methicillin or vancomycin
Prevent: Cover lesions and discard dressing; isolate infected children; no sharing of towels, clothing; laundry for infected clothing; WASH HANDS; treat carriers TOPICALLY (nose with mupirocin)

Question 3

Infected piercings/catheters: etiology, diagnosis,

Answer 3

Etiology: entry site of foreign materials can be infected by biofilms (large numbers of bacteria); think attachment of low-grade pathogens from normal skin flora that stick to foreign material; infected sites: decorative piercings, or catheters, iv lines, shunts, and other med devices; think STAPH EPIDERMIDIS which attaches to nylon and plastic
Diagnosis: clinical features (lab culture probably shows gram + cocci growing in clumps, catalase-pos, coagulase neg, non-hemolytic

Question 4

Treatment, Prevention of infected piercings/catheters:

Answer 4

Treatment: remove infected piercing/device; eliminate biofilms by cleaning and antibiotics not likely to be effective
Prevent: change all indwelling catheters on a regular schedule; use gold or surgical stainless steel for decorative pierces, not plastic

Question 5

Scabies: etio, transmission, diagnosis, prevention, treatment:

Answer 5

Etio: Sarcoptes scabei, a mite, .5 mm long, eight legs; burrows into skin and lays eggs, makes linear lesions which itch severely (cell-mediated hypersens); itching worse at night, usually involves wrists or genitals
Transmission: personal contact or fomites
Diagnosis: clinical findings, plus observation of mites in skin scrapings
Prevention: Hygiene (change clothes regularly, discourage sharing of towels)
Treatment: topical steroids for itching, permethrin/malathion to kill mites

Question 6

Etiology of skin abscesses:

Answer 6

Localized collection of pus (liquified tissue). Abscesses may be deep or superficial, infected or sterile; forms of abscesses: 1. farunculitis (superficial sweat gland or follicle infection) 2. carbuncle (multiple abscesses fused sc) 3. Stye 4. Acne
Skin abscesses usually due to S aureus, and multiple non-pathogenic skin bacteria; in acne, P. acnes is anaerobic bacterium usually present simultaneously

Question 7

Diagnosis, Treatment, prevention of skin abscesses:

Answer 7

Diag: clinical appearance, history; smears from pus show mixed bacterial pops, including gram pos cocci, coag-pos, beta hemolytic, DNAse-positive, salt-resistant, other organisms
Treatment: drain abscesses (remove dead tissue, cover with dry dressing); mupirocin ointment for mild; systemic antibiotics if severe with nafcillin or oxacillin with cephalosporin as alternative;
drug sens testing might be needed (could be susceptible to clinda or methicillin, if not then vancomycin or linezolid, some MRSA are resistant to all antibiotics): need to multiple agents to reduce skin susceptibility and multiple empirical topical or systemic antibiotics for acne
Prevention: remove carriers from ICUs, operating rooms, newborn nurseries; carrier state can often be eliminated by topical Mupirocin ointment to nares

Question 8

For Scalded Skin Syndrome, what is this?

Answer 8

widespread exfoliation due to localized infection by S aureus; exfoliatin toxin causes separation b/w epidermal cells; usually seen in newborns

Question 9

Toxic shock syndrome is

Answer 9

systemic immune rxn to super-antigen TSST or strep TSST

Question 10

Erysipelas/cellulitis/necrotizing fasciitis etiology

Answer 10

Etiology: infections beneath skin surface that spread in diffuse manner, with erysipelas superficial, cellulitis deeper and associated with LAD, fever, and bacteremia;
necrotizing fasciitis: minor skin infection which becomes rapidly extensive, spreading through subcutaneous fascia with widespread necrosis and gangrene of extremities (no predisposing factors);
each of these conditions USUALLY DUE TO strep pyogenes (necrotizing fasciitis with potent protease enzyme)

Question 11

Diagnosis, treatment of erysipelas, cellulitis, NF?

Answer 11

Diagnosis: clinical features; cultures from tissue or blood often negative; strep is assumed
Treatment: erysipelas and cellulitis, use penicillin or cephalosporin; necrotizing fasciitis, rapid surgical intervention, including amputation of affected digits or limbs, culture and sens testing

Question 12

Surgical site infections:

Answer 12

approx 2.5% of surgical patients acquire infection of surgical site, usually strep or staph;
they come 5 days to 2 weeks after surgery;
strep appears similar to celluitis, staph can lead to toxic shock syndrome;
TREAT: local excision and drainage; try to eliminate Staph carrier state before surgery to reduce post-surgical infection

Question 13

S aureus virulence factors include:

Answer 13

Structural: protein A, capsule, coagulase;
Toxins: DNAse, enterotoxin, exfoliatin, leukocidin, TSST