Skin and Soft Tissue Infections

Question 1

Skin and Soft Tissue Infections

types

Answer 1

The location of the infection the depth of the infection the idea logic cause or which bacteria is may be causing it the clinical setting

• Impetigo
• Folliculitis, Furuncles, andCarbuncles
• Erysipelas
• Cellulitis
• NecrotizingFasciitis

Question 2

which infections in:
epidermis
dermis
superficial fascia
subq tissue
muscle

read

Answer 2

epi: erysipelas, impetigo, folliculitis
dermis: ecthyma, furunculosis, carbunculosis

superficial fascia: cellulitis
subq tissue: necrotizing fascitis
muscle: nyonecrosis

Question 3

Epidemiology

Answer 3

• Skin and soft tissue infections (SSTIs) are among the most
common types of infection seen in ambulatory and
hospital settings
• Significant infection may occur at any age
▫ But more common in those ≥ 50 years old
• Minor local trauma as the initial pathogenic event is
common

Question 4

Cellulitis and Erysipelas

signs and minimum criteria

Answer 4

Rapidly spreading, diffuse skin infection including the
dermis and subcutaneous tissues
Signs - erythema, edema, and heat
• occasionally accompanied by lymphangitis and inflammation of the regional lymph nodes
• (excluding infections with underlying foci or collection of pus e.g., Abscesses, necrotizing fasciitis, or osteomyelitis)
• Skin surface may resemble an orange peel due to edemasurrounding hair follicles
• Systemic symptoms usually mild but may have fever,
tachycardia, confusion, hypotension, and leukocytosis even before skin symptoms appear

needs to have: redness warmth swelling and pain and typically unilateral involvement (extremities, one leg only)

Question 5

Cellulitis and Erysipelas
Infection arises through breaks in skin, often imperceptible
Predisposing factors are those that make skin more fragile or local host defenses less effective

Answer 5

Predisposing factors are those that make skin more fragile or
local host defenses less effective
• edema from venous insufficiency or lymphatic
obstruction
• previous cutaneous damage or cellulitis
• Pre-existing skin infections (impetigo, ulceration, fissured toe webs, eczema)
• Obesity

Question 6

• Erysipelas has 2 distinguishing features

Answer 6

• Erysipelas affects the upper dermis including the superficial lymphatics (usually S. pyogenes, group A diff serotype than ones for pharyngitis)
• Cellulitis involves the deeper dermis and subcutaneous fat

• Erysipelas has 2 distinguishing features
• Lesions are raised above the level of the surrounding
skin
• There is a clear demarcation between involved
and uninvolved tissue

Question 7

Erysipelas

likely pathogen

Answer 7

• More common in infants, young children, and older adults
• Almost always caused by Grp A b-hemolytic streptococci pyogenes
(some Grp B, C, F or G)
• Rarely S. aureus (MSSA or MRSA)
• In past, erysipelas referred to butterfly distribution on
face; now found more often on lower extremities

Question 8

Cellulitis/Erysipelas Treatment

Answer 8

• With early diagnosis and treatment, prognosis is excellent
• Infection may extend to deeper levels of skin and soft tissues
• Cultures of blood, tissue aspirates, or skin biopsies not normally necessary unless severely ill, immunocompromised, malignancy, animal bites etc.
• Blood cultures only positive in < 5% patients,
• needle aspirations positive in 5 - 40%,
• punch biopsy positive 20 – 30%

skin swabs not useful as they tell yu waht’s going on the surface

Question 9

Erysipelas Treatment

general

Answer 9

• Most patients can receive oral treatment x 5 days*
• An agent active against Grp A streptococci should be treatment of choice (strong)
• Some clinicians may choose to add coverage against MSSA(weak)
• Many would cover for MRSA if (nasal carriage, purulent drainage, injection drug use, SIRS)
• In severely compromised patients with severe infection, broad spectrum coverage can be used
• e.g., Vancomycin plus either piperacillin/tazobactam or
imipenem or meropenem

Question 10

Erysipelas Treatment
No/Mild systemic symptoms

Extremities: elevation of affected limb very important
→ leg, elevate higher than hip; arm, elevate higher than shoulder

Answer 10

No/Mild systemic symptoms
• Penicillin VK 250-500 mg PO QID
• Amoxicillin 500 mg PO TID
• If penicillin/amoxicillin allergy^: Cefuroxime 500 mg PO BID
• If cefuroxime allergy^: Clindamycin 300 mg PO QID

last 3 options for 5 days*
* If minimal response at 3 days, treatment duration = 7-10 days total extended

Question 11

Erysipelas Treatment

Moderate-Severe systemic symptoms

Answer 11

• Penicillin G 2-4 MU IV q4-6h
• Ampicillin 2 g IV q6h
• If penicillin/ampicillin allergy^: Cefazolin 2 g IV q8h
• If cefazolin allergy^: Ceftriaxone 1 g IV daily
• If cefazolin and ceftriaxone allergy^: Clindamycin 600 mg IV q8h
or Vancomycin (dosed to target trough 10-20 mg/L)

x 5-10 days # Total duration depends on response to therapy. Reassess at 3 days for potential
switch to oral therapy. Treat for 10 days if risk of treatment failure
eg. if infection is overlying a joint, chronic leg ulcers, same area b4

Question 12

Cellulitis

gneral

Answer 12

• Acute spreading of skin that extends deeper than erysipelas
• Involves the subcutaneous tissues
• Group A Streptococcus, other -hemolytic streptococci, and
Staphylococcus aureus are most common causes
• Involved area is often extensive, with marked erythema, warmth, and swelling.
• In contrast to erysipelas, borders of cellulitic area are not elevated and sharply demarcated.
• Regional lymphadenopathy is common and bacteremia can occur
▫ Serious because of propensity of infection to spread via lymphatics and bloodstream

Question 13

Cellulitis Treatment

Mild

Answer 13

• Cloxacillin 500 mg PO QID
• Cephalexin 500-1000 mg PO QID
• If penicillin and cephalexin allergy^: Cefuroxime 500 mg PO BID
• If cefuroxime allergy^: Clindamycin 300 mg PO QID

x 5 days* If minimal response at 3 days, treatment duration = 7-10 days total

Question 14

Moderate-Severe cellulitis

Answer 14

• Cloxacillin 1-2 g IV q6h x 5-10 days
• Cefazolin 1-2 g IV q8h x 5-10 days
• If penicillin and cefazolin allergy^: Ceftriaxone 2 g IV daily
• If ceftriaxone allergy^: Clindamycin 600 mg IV q8h or 300 mg PO QID

x 5-10 days#
Total duration depends on response to therapy. Reassess at 3 days for potential
switch to oral therapy. Treat for 10 days if risk of treatment failure

Question 15

Recurrent Cellulitis

Answer 15

• Patients with previous attack of cellulitis, especially
involving the legs have recurrence rates of 8 - 20%/yr
• Usually in the same area
• Attempt to resolve predisposing factors – edema,
obesity, toe fissures, venous insufficiency

• Prophylactic antibacterials may be considered if 3 - 4
episodes of cellulitis per yr despite attempt to treat
predisposing factors (weak, moderate)
• Oral penicillin VK 250 mg bid x 4 - 52 wks
• IM benzathine penicillin 1.2 MU q 4 wks
• If penicillin allergy: azithromycin 250 mg po daily
clarithromycin 500 mg po daily

Question 16

purulent vs nonpurulent classification (mild, moderate, severe)

read

Answer 16

Mild infection: for purulent SSTI,
incision and drainage is indicated. Moderate infection: patients with purulent infection with
systemic signs of infection. Severe infection: patients who have failed incision and drainage plus
oral antibiotics or those with systemic signs of infection such as temperature >38°C, tachycardia
(heart rate >90 beats per minute), tachypnea (respiratory rate >24 breaths per minute) or
abnormal white blood cell count (<12 000 or <400 cells/µL), or immunocompromised patients.

Nonpurulent SSTIs. Mild infection: typical cellulitis/erysipelas with no focus of purulence.
Moderate infection: typical cellulitis/erysipelas with systemic signs of infection. Severe infection:
patients who have failed oral antibiotic treatment or those with systemic signs of infection (as
defined above under purulent infection), or those who are immunocom- promised, or those with
clinical signs of deeper infection such as bullae, skin sloughing, hypotension, or evidence of
organ dysfunction.

Question 17

Risk Factors for MRSA

Answer 17

• Previous colonization or infection with MRSA (means lower threshold fro covering MRSA as stakes are higher)
• Recent hospitalization (particularly if received IV antibacterials)
• Rapid onset/progression
• Injection (IV) drug use

Question 18

When to Suspect MRSA

Answer 18

• Severe infections compatible with S. aureus
• When risk factors for MRSA are present
• When poor response to b-lactam therapy in
individuals with presumed staphylococcal infection

Question 19

Treatment of MRSA in SSTI - mild

Answer 19

Mild (Infected scratches, insect bites, furuncles,
small abscesses, not systemically ill)
• Cover draining lesions
• No antibacterials recommended (unless
immunocompromised or young infant)
• Emphasize personal hygiene
• Close follow-up (Return if worsening)

Question 20

Treatment of MRSA in SSTI - mild-moderate

Answer 20

• Cellulitis, moderate abscesses, minimal/no systemic features
• Culture (blood if febrile)
• Drainage or needle aspiration
• Oral therapy - older child or adult (parenteral if young)
• Infection Control
• Follow-up
• Clindamycin 150-450 mg q6h po (83% S Edmonton 2020) or
• TMP/SMX i-ii DS tab bid (94% S) (± Group A Strep coverage) or
• Doxycycline 100 mg q12h (94% S) (± Group A Strep coverage) or
• Linezolid 600mg q12h

Question 21

UAH and Community 2020 – % MRSA susceptible

Answer 21

UAH Community Edmonton
q Tetracycyline 94% 94%
q TMP/SMX 93% 94%
q Clindamycin 77% 83% (was 88% in 2007) (dont rely if you have other options unless you know susceptible)
q Linezolid 100%
q Vancomycin 100% 100%

Question 22

Treatment of MRSA in SSTI - severe

Answer 22

Extensive cellulits, large or multiple abscesses,
systemic symptoms
• Culture (blood if febrile)
• Drainage of abscess
• Hospitalize
• Parenteral Therapy
• Infection Control
• Infectious Disease Consult
• Imaging for extent

• Vancomycin ± [cloxacillin or 1st generation cephalosporin] –> if it comes back as MSSA or MRSA stop whichever is not necessary (if MRSA stop cefazolin, MSSA stop vanco not as good as b-lactam)
• Clindamycin may be added if toxin-mediated syndrome

Question 23

Diabetic Foot Infection

Answer 23

Complicate initially uninfected ulcerations that follow minor trauma, particularly when peripheral neuropathy, chronic neuropathic ulcers, or vascular insufficiency.
• May become cellulitis, soft tissue necrosis, or osteomyelitis with a draining sinus
• Prevention is very important – proper foot care, glycemic control

Question 24

Diabetic Foot Infection

common pathogens

Answer 24

S. aureus and -hemolytic strep frequently causative for cellulitis or mildly infected ulcers
• More chronic lesions and those previously treated with antibacterials may also have Enterobacterales; macerated lesions may contain
non-enteric Gram-negative bacilli (i.e., Pseudomonas aeruginosa)
• Chronic refractory ulcers (especially if gangrenous) can have a wide variety of organisms, including the above and enterococci, anaerobes,nand sometimes fungi

Question 25

Diabetic Foot Infection - Management

Answer 25

• Surgical debridement (necrotic tissue) and drainage so abx gets into crhonic tissue
• Wound care

• Antibacterial therapy:
▫ Antipseudomonal coverage not always necessary (P. aeruginosa often a non-pathogenic colonizer). Empiric coverage considered if:
 Tropical/warm climate
 Soaking of feet
 Failed non-antipseudomonal therapy
 Limb-threatening infection

▫ MRSA coverage if:
 Current or previous (within 12 months) colonization/infection with MRSA
 Recent antibacterial use
 Recent hospitalization

Question 26

Diabetic Foot Infection – Antibacterial Management

Mild or simple cellulitis

Answer 26

Treat as per cellulitis → coverage for S. aureus and GAS (group A strep)

Question 27

Diabetic Foot Infection – Antibacterial Management
Ulcer, drainage, fistula

Usual pathogens (often polymicrobial):
S. aureus/MRSA, other Staphylococci
-hemolytic Streptococci
Enterococcus spp
Enterobacterales
Pseudomonas spp
Anaerobes
mild

Answer 27

Mild*
• Amoxicillin-clavulanate 875 mg PO BID
• If penicillin/amoxicillin allergy^: Cefuroxime 500 mg PO BID
+ Metronidazole 500 mg PO BID
• If cefuroxime allergy^: Doxycycline 100 mg PO BID + Metronidazole

x 7-14
days (dependent on clinical response)

Question 28

Diabetic Foot Infection – Antibacterial Management
Ulcer, drainage, fistula - mod-severe

Usual pathogens (often polymicrobial):
S. aureus/MRSA, other Staphylococci
-hemolytic Streptococci
Enterococcus spp
Enterobacterales
Pseudomonas spp
Anaerobes

Answer 28

• Cefazolin 2g IV q8h + Metronidazole 500 mg PO BID
• If cefazolin allergy^: Ceftriaxone 2 g IV daily + Metronidazole

x 7-14
days (dependent on clinical response)

*If MRSA suspected: add MRSA-active agent

Question 29

Diabetic Foot Infection – Antibacterial Management

Limb-threatening

Answer 29

• Piperacillin-tazobactam 3.375g IV q6h + Vancomycin (dosed to target trough 10-20 mg/L)
• If penicillin allergy^: Imipenem 500 mg IV Q6H + Vancomycin

Question 30

Necrotizing Fasciitis

symptims
progression

Answer 30

• Rare aggressive subcutaneous infection that tracks along fascial planes and extends well beyond the superficial signs of infection
• Name ‘fasciitis’ sometimes leads to the mistaken impression that the muscular fascia is involved (occurs above it)
• However, fascia referred to is the ‘superficial fascia’ comprised of all of the tissue between the skin and underlying muscles (subcutaneous tissue)
• Extension from a skin infection in 80% of cases
• Usually, initial lesion is trivial – mild abrasion, insect bite,injection site, boil
• 20% have no visible skin lesion
• Initially pain may be out of proportion to apparent skin lesion

• Initial presentation is cellulitis which can advance
rapidly or slowly
• As progresses, high fevers with systemic toxicity,
disorientation, lethargy
• Subcutaneous tissues have a wooden-hard feel
• Often deep-seated and devastating resulting in major
tissue destruction and death

Question 31

Necrotizing Fasciitis

common pathogens

Answer 31

• Toxin producing S. pyogenes, S. aureus, are the major
pathogens and may occur simultaneously
• Most cases are community acquired and present in the limbs (2/3 in lower extremities)
• Often an underlying cause
• diabetes
• arteriosclerotic vascular disease
• venous insufficiency and
• edema
• venous stasis
• vascular insufficiency
• ulcer

Cases after trivial causes are often S. pyogenes (mortality rate in this group with hypotension and organ failure is high (50 - 70%))
• Occasionally polymicrobial with mixed aerobic/anaerobic infection mostly from bowel
• Following surgical procedures
• Decubitus ulcers
• Perianal abscess
• Bartholins gland abscess

Question 32

Diagnosis

Answer 32

• appearance of subcutaneous tissue and fascial planes
with surgery important in diagnosis
• Cellulitis, edema, skin discoloration
• Wooden-hard feel of subcutaneous tissues
• Appearance of fascia at surgery
• Swollen, dull grey, stringy areas of necrosis, thin brownish
exudate, no true pus
• Gram stain at surgery

Question 33

Necrotizing Fasciitis Treatment

Answer 33

• Surgical intervention and debridement the major
therapeutic modality (A-III)
• Unresponsive to antibacterials alone –> clean up any mess and prevent getting into blood
• Profound toxicity, fever, hypotension or advancement
• Any soft-tissue infection accompanied by gas suggests
necrotic tissue
• Surgery q24-36hr as necessary for debridement

Question 34

Necrotizing Fasciitis - Antibacterial Treatment

Community-acquired Necrotizing Fasciitis
• Caused by Grp A Streptococci and/or S. aureus
• May result in streptococcal toxic shock syndrome

Answer 34

Empiric Treatment
• Ceftriaxone 2 g IV daily x 10-14 days
+ Clindamycin 600-900 mg IV q8h

Treatment of documented GAS
• Penicillin 4 MU IV q4h plus Clindamycin 600-900 mg IV q8h (strong, low)
• Clindamycin added based on in vitro studies demonstrating both toxin suppression and modulation of TNF production

linezolid can also help with toxin pdtn

Question 35

Necrotizing Fasciitis

empiric treatment for Polymicrobial Infections (mostly from bowel)
• Following surgical procedures, decubitus ulcers, perianal abscess, Bartholins gland abscess

need broad coverage

Answer 35

• Should be broad polymicrobial (directed at aerobic and
anaerobic pathogens)
• Vancomycin plus [piperacillin/tazobactam or a carbapenem];
or plus [ceftriaxone and metronidazole] (strong,low)

Question 36

Prophylaxis of Group A Streptococcal Toxic Shock
Syndrome/Necrotizing Fasciitis

pt with close contact

Answer 36

• Prophylaxis recommended for contacts of Grp A
streptococcal toxic shock syndrome or necrotizing
fasciitis
• Cephalexin 250 mg po qid x 10 days
(or 500 mg bid x 10 days)
• 2nd line Erythromycin, Clarithromycin, or Clindamycin
x 10 days

Question 37

• Mr G. is a 65 year old ♂ who presents to your ambulatory clinic
complaining of redness and swelling of his left lower leg. On examination, the area in question is indeed erythematous, swollen, and warm and tender to the touch with borders that appear difficult to
demarcate. The right leg does not appear to have any erythematous or swollen lesions and is described as normal by the patient. He states that it started as a small lesion a couple weeks ago, that has progressively worsened. He denies any recent traum to the area and has never had a skin infection as extensive as this one (and not for many years, either).
The area now measures approximately 7 inches by 5 inches. His BP is 130/84, HR 70, RR 20, temperature 37.2ºC, and he weighs 110 kg. He states that he previously was very healthy and fairly active and only
takes candesartan for HTN (no other medications on Netcare going back two years).

Answer 37

inflamm, swelling, unilateral presentation, difficult to demarcate
cellulitis
normal bp, not febrile
severity: mild, not large area, slow progression, pt is helthy

more info: no to allergies, purulence, injectiond rug user

GroupA strep more likely, MSSA possible

Cephalexin 1g PO QID (1g because of weight of pt >100kg greater Vol of distibution) x 5days
f/u at 3 days to see respond and potentially extend