IC14 SSTI Flashcards by peepoo heh

How do SSTIs come about? (Pathogenesis)

Disruption of normal host cell defenses (eg. skin break) –> allows overgrowth & invasion of skin and soft tissue by pathogenic microorganisms

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What are the risk factors for SSTIs?

disruption of skin barrier
- traumatic causes (lesions, abrasions, burns, surgery, bites from humans/animals/insects, IV drug use)
- nontraumatic causes (ulcers, tinea pedis, dermatitis, chemical irritants)
- impaired venous & lymphatic drainage
- peripheral artery disease
conditions that predispose to infection
- DM, cirrhosis, neutropenia, HIV, transplant, immunosuppression
history of cellulitis

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How do you prevent SSTIs?

management of risk factors
good wound care
treat tinea pedis
prevent dry, cracked skin
good foot care for DM patients to prevent wounds & ulcers
removal of foreign objects, irrigation, tissue debridement

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How do you diagnose a SSTI?

physical exam & patient history

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Where should you and should you NOT take samples for cultures for SSTIs from?

do NOT take cultures from:
- open, draining wounds (v likely contaminated)
- wound swabs

take cultures from:
- deep in the wound after surface cleansed
- base of closed abscess
- curettage > wound swab/irrigation (debridement of top layers before taking tissue sample)

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Do you need to take blood samples for SSTIs?

Only for severe SSTI or immunocompromised patients

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Describe impetigo

erythematous papules that develop into vesicles and pustules that rupture, with the dried discharge forming a honey-colored crust on a erythematous base

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Describe ecthyma

ulcerative form of impetigo that occurs in deeper skin layers (not a progression of impetigo; they are diff SSTIs)

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Describe furuncles and carbuncles

furuncle (boil) - infection of hair follicle
carbuncle - group of furuncles

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Describe skin abscesses

collection of pus within dermis and deeper skin tissue; painful, tender and red nodules

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Describe erysipelas

fiery red painful plaque (raised above surrounding skin) with well-demarcated edges; common on face and lower extremities

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Describe cellulitis

involves deeper and subq fats; acute, diffuse, spreading, non-elevated, poorly demarcated area of erythema, mostly unilateral (on one limb); typically in lower extremities

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What are the likely pathogens for each SSTI?

impetigo: Staph, strep pyogenes
ecthyma: Strep pyogenes (GAS)
nonpurulent (cellulitis, erysipelas): Strep pyogenes
purulent (purulent cellulitis, furuncles, carbuncles, skin abscesses): Staph aureus, Strep pyogenes

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What are the two kinds of MRSA that can cause SSTIs?

community-acquired MRSA
healthcare-associated MRSA

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How are the two MRSAs different?

CA-MRSA and HA-MRSA are genetically different
1. PVL (Panton-Valentine leucocidin) [cytotoxin]
2. SCCmec (CA: IV, HA: II) [mobile genetic element for novel specific PBP2a]

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Describe the prevalence of the two MRSAs involved in SSTIs

CA-MRSA: More common in USA
HA-MRSA: Usually almost always HA-MRSA in SG, so have to treat as long as patient has MRSA risk factors

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Define HA-MRSA

patient develops MRSA infection within
1. 2 days of being in hospital
2. 12 months of being discharged from hospital

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What are the risk factors for HA-MRSA?

antibiotic use
recent hospitalization/surgery (for a decent duration; doesn’t count if just visiting etc)
prolonged hospitalization
ICU
hemodialysis
MRSA colonization
close proximity to MRSA colonized/infected people

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Describe the treatment for mild impetigo (limited lesions)

Likely pathogen: Staph (MSSA), strep

THEORY: Topical mupirocin BD x 5/7
NOT recommended; reserved for MRSA decolonization in hospitals

IN PRACTICE: no need to treat as self-limiting

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Describe the EMPIRIC treatment for impetigo/ecthyma (multiple lesions)

Likely pathogens:
impetigo: Staph (MSSA), strep
ecthyma: grp A strep

PO beta lactams
- Cloxacillin
- Cephalexin
PO Clindamycin (penicillin allergy)

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Describe the CULTURE-DIRECTED treatment for impetigo/ecthyma (multiple lesions) if it is caused by
1. Strep pyogenes (Grp A strep)
2. MSSA

Strep pyogenes:
1. PO penicillins
- Pen V
- Amoxicillin

MSSA:
1. PO beta lactams
- Cloxacillin
- Cephalexin

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What is the typical treatment duration of impetigo & ecthyma for
1. mild infection
2. moderate to severe infection

5-7 days
moderate to severe: 10-14 days

What is the main treatment for purulent SSTIs (purulent cellulitis, furuncles, carbuncles, skin abscesses)?

incision & drainage (source control)

When do we use antibiotics for purulent SSTIs?

unable to drain completely
lack of response to I&D
extensive disease involving many sites
extreme ages (v young/old)
immunosuppressed
signs of systemic illness (2/4 of SIRS criteria)
IV abx for severe disease state

Describe the SIRS criteria

SIRS = systemic inflammatory response syndrome 1. temp (>38 or <36) 2. WBC (>12 or <4) 3. HR (>90) 4. RR (>24)

Describe the treatment to be given for purulent SSTIs that are 1. mild 2. moderate 3. severe

Likely pathogens: Staph aureus (MSSA) 1. I&D + warm compress 2. I&D + PO abx - Cloxacillin - Cephalexin - Clindamycin (Penicillin allergy) 3. I&D + IV abx - Cloxacillin - Cefazolin - Clindamycin - Vanco

Describe the empiric treatment to be given for purulent SSTIs that involve MRSA

PO - co-trimoxazole - doxycyline - clindamycin IV - vanco - daptomycin - linezolid (daptomycin & linezolid reserved for VRE/vanco allergy)

What happens if purulent SSTI occurs near perioral/perirectal/ vulvovaginal areas?

add G(-) anaerobic coverage

Describe the empiric treatment to be given for purulent SSTIs that involve G(-) anaerobes

amoxicillin-clavulanate (Augmentin) pip-tazo (if risk of resistant strain) carbapenem (if super duper sick)

What is the typical treatment duration for purulent SSTIs?

5-10 days

Describe the treatment to be given for nonpurulent SSTIs that are 1. mild 2. moderate 3. severe

Likely pathogen: Grp A strep 1. PO abx - Pen V - Amoxicillin - Cloxacillin - Cephalexin - Clindamycin (penicillin allergy) 2. moderate = signs of systemic ifxn + some purulence; IV abx - Ampicillin - Cloxacillin - Cefazolin - Clindamycin (penicillin allergy) 3. severe = signs of systemic ifxn/failed oral therapy/immunocompromised; broader coverage + possibility of necrotizing fasciitis IV - Pip-tazo - Cefepime (4th gen) - Meropenem if MRSA risk factors - Vanco, daptomycin, linezolid

Describe the treatment to be given for non-purulent SSTI in a patient with a history of water exposure

+ Cipro to cover Aeromonas, Vibrio & Pseudomonas

What is the typical duration of treatment for nonpurulent SSTIs?

5-10 days 14 days for immunocompromised

What are some other things to do when treating nonpurulent SSTIs?

1. rest 2. limb elevation to promote drainage of edema 3. treat underlying conditions (eg. tinea pedis, skin dryness, limb edema)

What are the monitoring parameters when monitoring for therapeutic response of SSTI treatment?

- improvement within 2-3 days (won't resolve so fast) - no progression of lesions/development of complications - reassess indication/choice of abx if no improvement within 2-3 days

How do DFIs (diabetic foot infections) come about? (Pathogenesis)

1. risk factors - neuropathy (loss of sensation) - vasculopathy (poor circulation) - immunopathy 2. ulcer formation/wound 3. bacterial colonize, penetration, proliferation 4. DFIs

What constitutes DFIs?

- wounds - ulcers

When do we treat wounds and ulcers found in diabetic patients?

if infected (ie. true DFI) criteria for infection: 1. purulent discharge, or 2. at least 2 signs of inflammation - erythema - warmness - tender - pain - induration (thickening/hardening of skin)

What are the microbes involved in DFIs?

typically polymicrobial G(+) - Staph, Strep G(-) (for wet/chronic wounds) - Proteus, Klebsiella, E Coli Anaerobes (for deep/ischemic/necrotic wounds) - Peptostreptococcus (Finegolda magna in SOA table) - Veillonella - Bacteroides

When and how do we take cultures for DFIs?

no need for mild DFI need for moderate to severe DFI take deep tissue cultures after cleansing + before starting empiric abx - avoid skin swabs - do not culture uninfected wounds

What is the criteria for mild DFI?

- involves skin + SQ tissue, AND - erythema ≤2cm, AND - no signs of systemic infection

What are the organisms to cover for mild DFI?

- Staph aureus - Strep species

What are the antibiotics to use for mild DFI?

PO abx - Cloxacillin - Cephalexin - Clindamycin if MRSA risk factors (PO) - Co-trimoxazole - Doxycyline - Clindamycin

What is the criteria for moderate DFI?

- involves deeper tissues (eg. bones, joints), OR - erythema >2cm - no signs of systemic infection (compulsory)

What are the organisms to cover for moderate DFI?

G(+) - Staph - Strep G(-) - +/- PA anaerobes

What are the antibiotics to use for moderate DFI?

IV abx - Amox/clav (Augmentin) - Cefazolin/Ceftriaxone + Metronidazole if MRSA risk factors (IV) - Vanco - Daptomycin - Linezolid

What is the criteria for severe DFI?

- involves deeper tissues (eg. bones, joints) OR - erythema >2cm - signs of systemic infection (compulsory)

What are the organisms to cover for severe DFI?

G(+) - Staph, strep G(-) - PA anaerobes

What are the antibiotics to use for severe DFI?

IV abx - Pip-tazo - Cefepime + metronidazole - Meropenem - Cipro + clindamycin if MRSA risk factors (IV) - Vanco - Daptomycin - Linezolid

What is the recommended duration of therapy for DFIs 1. not involving bones (mild, moderate, severe) 2. involving bones A: surgery - infected tissue completely removed, residual infected tissue left, residual viable bone left B: no surgery

Not involving bones * mild: 1-2 wks * moderate: 1-3 wks * severe: 2-4 wks Involving bone * surgery, complete removal: 2-5 days * surgery, residual infected tissue: 1-3 wks * surgery, residual viable bone: 4-6 wks * no surgery: ≥3 months

What are some adjunctive measures for DFIs?

* wound care * foot care * glycemic control

What are some risk factors for pressure ulcers?

1. reduced mobility 2. impaired immunity

When do we treat pressure ulcers with antibiotics?

when it becomes infected, meaning 1. purulent discharge 2. ≥2 signs of inflammation (erythema, warmness, tender, pain, induration)

What are some adjunctive measures for pressure ulcers?

1. debridement of infected/necrotic tissue 2. local wound care 3. relief pressure