Skin and Soft Tissue Infections

What are risk factors for community acquired MRSA infections?

children, health care professional, and military personnel

What are risk factors for hospital required MRSA?

diabetes mellitus, dialysis (peritoneal, hemodialysis), long term care, long term IV access, and prolonged hospitalizations

What are predisposing factors for necrotizing fasciitis?

alcohol abuse, diabetes mellitus, poor nutrition, sports participation, and trauma

What bacteria most commonly cause SSTIs?

S. aureus and beta-hemolytic streptococci

What bacteria less frequently cause SSTIs?

gram negative organisms, anaerobes, yeast and mixed infections

What conditions effect the epidermis?

erysipelas, impetigo, and folliculitis

What conditions effect the dermis?

ecthyma, furunculosis, and carbunculosis

What conditions effect the superficial fascia?

cellulitis

What conditions effect the subcutaneous tissue?

necrotizing fasciitis

What conditions effect the muscle tissue in the deep fascia?

myonecrosis (clostridial and nonclostridial)

What are the clinical presentation of SSTIs?

erythema, swelling, warmth, induration, pain/tenderness to palpation, draining wound

What signs and symptoms of systemic illness may accompany skin symptoms?

fever/chills, diaphoresis, malaise, and elements of SIRS criteria

What conditions are purulent SSTIs?

furuncles, carbuncles, and cutaneous abscesses

What is a cutaneous abscess?

collection of pus within the dermis and deeper skin tissues; painful, fluctuant red nodules, often topped with pustule, rim of erythematous swelling

What is a furuncle?

boils; infection of single hair follicle

What is a carbuncle?

collection of infected follicles

What layers of the skin do purulent SSTIs effect?

the epidermis and dermis

How do you diagnosis purulent SSTIs?

gram stain and culture of pus/exudates are recommended but not required (except in impetigo its highly recommended)

Majority of purulent SSTIs are caused by which bacteria?

staphylococcus aureus

What is the overall treatment plan for purulent SSTIs?

drainage ± antibiotics

Why is incision and drainage (I&D) a MUST for purulent SSTIs?

• furuncles may spontaneously rupture and drain

  • gram stain and culture of pus is recommended and easier if drained (except cysts)

When would you add an antibiotic to the treatment of purulent SSTIs?

if patient has systemic signs of infection, is immunocompromised, has multiple abscess, or doesn’t respond to I&D

What is the duration of therapy for purulent SSTIs?

5-10 days of therapy following I&D

What is a mild SSTI?

no systemic signs of infection

What is a moderate SSTI?

systemic signs of infection but hemodynamically stable

What is a severe purulent SSTI?

failed I&D + antibiotics OR multiple systemic signs + acute hypotension/organ dysfunction OR immunocomprimised

What are the SIRS criteria? (systemic inflammatory response syndrome)

elevated temp (>38), tachycardia (>90), tachypnea (>24), abnormal WBC (>12,000 or <400)

What are the empiric drug choices for severe purulent SSTIs?

vancomycin, daptomycin, linezolid, telavancin, or ceftaroline

What are the empiric drug choices for moderate purulent SSTIs?

TMP/SMX or doxycycline

What specific bacteria do the empiric drug choices for purulent SSTIs cover?

MRSA

What are the defined MSSA drug choices for severe purulent SSTIs?

nafcillin, cefazolin, or clindamycin

What are the defined MSSA drug choices for moderate purulent SSTIs?

dicloxacilllin or cephalexin

What conditions are non-purulent SSTIs?

cellulitis and erysipelas

What layer of the skin do non-purulent SSTIs effect?

superficial fascia

What are the classic signs of cellulitis/ erysipelas?

“rubor, calor, tumor, dolor” → red, warm, swollen, and painful

What are the risk factors for non-purulent SSTIs?

dry skin, fragile skin, obesity, previous skin trauma, previous cellulitis, edema from venous insufficiency, tinea pedis (athlete’s foot)

Majority of non-purulent SSTIs are caused by which bacteria?

streptococcus species

What is the general treatment plan for non-purulent SSTIs?

antibiotics

Although drainage and cultures are not recommended for typical non-purulent SSTIs, when would they be?

immunodeficiency, cancer/chemotherapy

What is a severe non-purulent SSTI?

failed PO antibiotics OR multiple systemic signs + acute hypotension or organ dysfunction OR immunocompromised OR signs of deeper infection (such as bullae, skin sloughing)

What is the duration of therapy for mild cellulitis?

5 days usually sufficient as long as patient responds

What is the duration of therapy for moderate to severe cellulitis (hospitalized)?

10 to 14 days; possibly longer in difficult to treat cases

What is the pathophysiology of necrotizing fascitis?

deep infection involving the superficial fascia comprising all tissue between skin and muscles

What is Fournier’s Gangrene?

necrotizing infection of genitalia; involves the scrotum and penis or vulva; diabetes strong risk factor

True or False: necrotizing fasciitis is associated with a high mortality in the past decade (15% to 45%)

true

What monomicrobial bacteria cause necrotizing fasciitis?

streptococcus pyogenes, staphylococcus aureus, clostridium spp.

What polymicrobial bacteria cause necrotizing fasciitis?

mixed aerobic/ anaerobic flora

What clinical settings are most often associated with necrotizing fasciitis?

abdominal trauma or surgery

decubitus ulcers

IVDU— injection sites

spread from genital site

How can microbial invasion of the subcutaneous tissues occur in necrotizing fasciitis?

external trauma

direct spread from a perforated viscus

from a hematogenous source

What is the most important factor impacting survival of necrotizing fasciitis?

early diagnosis and adequate debridement within 24 hours

What are the objective diagnostic clues to diagnose necrotizing fasciitis?

severe systemic symptoms— fever, altered mental status

fast temporal progression

What are the subjective diagnostic clues to diagnose necrotizing fasciitis?

pain out of proportion!

What are the physical exam diagnostic clues to diagnose necrotizing fasciitis?

edema and tenderness beyond the redness, wood-hard induration of subcutaneous tissue, crepitus, skin necrosis

What imaging can be done for necrotizing fasciitis?

CT scan or MRI; may show gas in soft tissues, edema along fascia

True or False: necrotizing fasciitis is a surgical emergency

true

True or False: multiple surgical interventions are often required for necrotizing fasciitis

true

What kind of cultures should be taken for necrotizing fasciitis?

blood cultures and deep tissue cultures

What is the empirical treatment for necrotizing fasciitis?

vancomycin + one of the following:

P/T

a carbapenem

cefepime + metronidazole or clindamycin

ciprofloxacin + metronidazole or clindamycin

What is the duration of therapy for necrotizing fasciitis?

until debridement is no longer needed, patient clinically improved, or afebrile for 48-72 hours

What kind of bite wounds have the highest risk of infection?

ones to the hand and face

What needs to be considered when looking at a bite wound?

circumstantial source, magnitude of injury, magnitude of inflammation, and patient factors

What is the treatment for a bite wound?

pre-emptive treatment for 3-5 days for certain populations, otherwise prophylaxis is not generally recommended

What patients have an indication for prophylaxis antibiotics for a bite wound?

immunocompromised, advanced liver disease, significant edema in the affected area, moderate-severe injury (face), and penetration of periosteum or joint capsule

What kind of microbials are present in dog bites?

staph, strep, and pasturella

What antibiotics would you chose for a dog bite?

PO: amox/clauv 875/125 PO Q12h

IV: 2nd gen cephalosporin PLUS clindamycin or metronidazole

(alt: bactrim(preg), FQ, doxycycline, avoid macrolides)

What bacteria are present in human bites?

aerobic bacteria— strep, s. aures, elkenella, and anaerobes (fusobacterium, peptostrep, provotella

What antibiotics would you use for a human bite?

amox/clav (PO)

amp/sul (IV)

beta-lacta allergy: ertapenem (IV), FQ PLUS metronidazole

What is DFI?

diabetic foot infection

What is DFU?

diabetic foot ulcer

What two etiologies play a role in diabetic foot infections

peripheral arterial disease and peripheral neuropathy

What are some causes of diabetic foot infection?

polyneuropathy, peripheral artery disease, hyperglycemia

What is the clinical presentation of a diabetic foot infection?

arise from an ulcer or from wound caused by trauma; redness, warmth, swelling, tenderness, pain, purulent drainage

True or false: x-ray is recommended for all diabetic foot infections

true

What are signs of a more serious diabetic foot infection?

systemic signs, laboratory tests, complicating features, and current treatment

What is osteomyelitis?

bone sample with positive microbial histology

Should you culture a clinically uninfected wound?

no! its not necessary

When are cultures essential in diabetic foot infections?

in moderate and severe infections, multiple organisms are likely and multi-drug resistant organisms may be possible

Why shouldn’t you swab diabetic foot infections?

superficial swabs much less helpful than deeper tissue cultures or aspirates of purulent secretions

What aerobic gram-positive cocci is common in diabetic foot infection?

staphylococcus and streptococcus are most common, sometimes can be MRSA

What aerobic gram-negative bacilli is common in diabetic foot infection?

sometimes can be pseudomonas

What anaerobes are common in diabetic foot infection?

not many; play more of a role in moderate to severe infections

What are risk factors for MRSA in DFI?

history of MRSA colonization, severe infection, or extensive surgical procedures

What are risk factors for pseudomonas in DFI?

warm climate, frequent exposure to water

What are risk factors for MRSA or pseudomonas in DFI?

extensive antimicrobial use in past 30-60 days, history of infections for each, high local prevalence

What is empiric therapy for mild DFIs?

TMP/SMX or doxycycline (covers MRSA)

MSSA: cephalexin, amox/clauv, clinda

What is empiric therapy for moderate or severe DFIs?

MSSA: amp/sub, cefoxitin, ceftriaxone + metro, cipro + clinda, moxi, or ertapenem

MRSA: vanco, linezolid, dapto

Pseudomonas: P/T, cefepime

What is the route and duration of therapy for mild DFI?

oral; 1-2 weeks

What is the route and duration of therapy for moderate DFI?

oral or IV; 1-3 weeks

What is the route and duration of therapy for severe DFI?

IV; 2-4 weeks

When should you discontinue antibiotics for DFIs?

once clinical signs and symptoms of infection have resolved (NOT until the wound is healed)