Skin & Soft Tissue Infections
And Management of Animal Bites
David H. Spach, MD
Professor of Medicine
Division of Infectious Diseases
University of Washington, Seattle
Case History
• Which of the following is true regarding impetigo?
1.
2.
3.
4.
Penicillin is the optimal oral therapy
Group A Streptococcus alone causes more than 90% of cases
Amoxacillin is the optimal oral therapy
If localized, Mupirocin is an effective therapy
Impetigo (Pyoderma)

Cause
- Staphylococcus aureus & Streptococcus pyogenes
 Risk factors
- Economically disadvantaged
- Young children
 Clinical Manifestations
- Typically located on face and extremities
- Vesicles  Pustules  Honey-colored crusts
From: Bisno AL, Stevens DL. N Engl J Med 1996;334:240-6.
IDSA 2014 SSTI Guidelines
Treatment of Impetigo


Topical (for limited number of lesions): 7-day Rx
- Mupirocin ointment bid x 7d
- Retapamulin ointment x 7d
Oral: 7-day Rx
- Dicloxacillin
- Cephalexin
- Erythromycin
- Clindamycin
- Amoxicillin-CA
Source: Stevens DL, et al. Clin Infect Dis. 2014;59:e10-52.
Skin Lesions
IDSA 2014 SSTI Guidelines
Treatment of Ecthyma


Empiric Therapy
- Cephalexin x 7d
- Dicloxacillin x 7d
Suspected or Confirmed MRSA
- Doxycycline
- Clindamycin
- TMP-SMX
Source: Stevens DL, et al. Clin Infect Dis. 2014;59:e10-52.
Case History: Skin & Soft Tissue
Cellulitis


Cause
- Common: Streptococcus sp.& Staphylococcus aureus
- Less common: H. influenzae, S. pneumoniae, gram- bacilli
Risk Factors
- Local trauma, abrasion, or skin lesion
- Impaired lymphatic drainage of extremity
 Clinical Manifestations
- Typically located on extremities
- Local (tenderness, erythema, & warmth), fever, chills, leukocytosis
From: Bisno AL, Stevens DL. N Engl J Med 1996;334:240-6.
Sachs MK. Arch Dermatol 1991;127:493-6.
IDSA 2014 SSTI Guidelines
Treatment of Cellulitis


Oral Therapy
- Cephalexin
- Penicillin
Intravenous Therapy
- Penicillin
- Clindamycin
- Nafcillin
- Cephazolin
Source: Stevens DL, et al. Clin Infect Dis. 2014;59:e10-52.
Case History: Skin & Soft Tissue
From: Bisno AL, Stevens DL.
N Engl J Med 1996;334:240-6.
Erysipelas



Cause
- Common: Streptococcus pyogenes (Group A)
- Less common: Groups G, C, and B streptococci, S. aureus
Risk factors
- Local trauma, abrasions, impaired lymphatic drainage
Clinical Manifestations
- Superficial (raised) cellulitis with sharply demarcated border
- Involvement of lower extremities more common than face
- Blood cultures positive in only 5%
From: Chartier C et al. Int J Dermatol 1990;29:459-67.
Bisno AL, Stevens DL. N Engl J Med 1996;334:240-6.
Hand Cellulitis
Case History

A 62-year-old man is admitted to the hospital with cellulitis. Four
hours after admission he develops severe hypotension,
increased creatinine, and a rapidly advancing cellulitis.
Case History

A 56-year-old man with diabetes undergoes bone marrow
transplantation and has neutropenia. He develops a painful skin
lesion on his right 5th toe.
Necrotizing Skin & Soft Tissue Infections
Diagnostic Clues
 Bullous lesions
 Dark discoloration (blue/purple/grey)
 Subcutaneous gas
 Painful area that becomes anesthetic
 Systemic toxicity
 Rapidly advancing lesion
IDSA 2014 SSTI Guidelines
Treatment of Necrotizing Fasciitis


Empiric Therapy
Vancomycin or Linezolid
+
Piperacillin-tazobactam or Carbapenem
or
Ceftriaxone + Metronidazole
Confirmed Group A Streptococcus
- Clindamycin + Penicillin
Source: Stevens DL, et al. Clin Infect Dis. 2014;59:e10-52.
Case History: Skin & Soft Tissue
•
A 38-year-old man presents with fever and an abscess on his
right arm. The lesion is very firm and is surrounded by
erythema.
•
What would you recommend
- Do you need to I & D?
- Should you obtain cultures?
- Do you need antibiotics?
MRSA Soft Tissue Infection
MRSA Soft Tissue Infection
Structure of Gram-Positive Bacteria
Penicillin Binding Proteins
DNA
Cell Membrane
Cell Wall
Beta-Lactams: Mechanism of Action
Penicillin Binding Proteins
Beta-Lactam
Transpeptidation
Carboxypeptidation
DNA
Cell Membrane
Cell Wall
Methicillin-Susceptible Staphylococcus aureus
Beta-Lactam
Cell Wall Synthesis
DNA
Cell Membrane
Penicillin Binding Proteins
Cell Wall
Staphylococcus aureus: Methicillin Resistance
Penicillin Binding Proteins
Nafcillin
mecA
DNA
Cell Membrane
Cell Wall
Free Access
Source: Liu C, et al. Clin Infect Dis. 2011:52:1-38.
2010 IDSA Practice Guidelines
Therapy for CA-MRSA Skin & Soft Tissue Infection
• Simple Abscess or Boil
- Incision and Drainage
“For simple abscesses or boils, incision and drainage alone is
likely adequate, but additional data are needed to further define
the role of antibiotics, if any, in this setting.”
Source: Liu C, et al. Clin Infect Dis. 2011:52:1-38.
2010 IDSA Practice Guidelines
Therapy for CA-MRSA Skin & Soft Tissue Infection
• Simple Abscess or Boil
- Incision and Drainage
• Complicated Abscess
- Incision and drainage + antimicrobial therapy
Source: Liu C, et al. Clin Infect Dis. 2011:52:1-38.
2010 IDSA Practice Guidelines
Therapy for CA-MRSA Skin & Soft Tissue Infection
• Complicated Abscess
- Severe or extensive disease or rapid progression of cellulitis
- Signs and symptoms of systemic illness
- Associated comorbidities or immunosuppression
- Extremes of age
- Abscess in area difficult to drain (eg, face, hand, genitalia)
- Associated septic phlebitis
- Lack of response to incision and drainage alone
Source: Liu C, et al. Clin Infect Dis. 2011:52:1-38.
2010 IDSA Practice Guidelines
Therapy for CA-MRSA Skin & Soft Tissue Infection
• Empiric Therapy for Out-Patient Management
- TMP-SMX: 1-2 DS tabs PO BID
- Clindamycin: 300-450 mg PO TID
- Doxycycline: 100 mg PO BID
- Minocycline: 200 mg x1, then 100 mg PO BID
- Linezolid: 600 mg PO BID
• If Also Covering for Group A Streptococcus
- TMP-SMX + Amoxicillin: 500 mg PO TID
- Clindamycin
- Doxycycline/Minocycline + Amoxicillin: 500 mg PO TID
- Linezolid
Source: Liu C, et al. Clin Infect Dis. 2011:52:1-38.
Case History: Skin & Soft Tissue
• This rash began about 5 days after a skiing trip in Canada. The
rash itches. The patient is afebrile and otherwise doing well. In
exam, it appears the hair follicles are involved.
•
What do you think is going on?
Case History: Skin & Soft Tissue

A 28-year-old man presents with a 3-day history of sinusitis
symptoms and a 12-hour history of right eye swelling. He
has a temperature of 38.5°C, eyelid edema, and eyelid
erythema. He can not spontaneously open his right eyelid,
but his vision and extra-ocular movements are intact. The
most likely diagnosis is:
1.
2.
3.
4.
Blepharitis
Varicella-Zoster infection
Preseptal (periorbital) cellulitis
Postseptal (orbital) cellulitis
Case History: Skin & Soft Tissue

A 33-year-old man cut his hand on a piece of broken glass
while cleaning out an aquarium. Several weeks later he noted
a painful, draining nodule on his hand. He now has several
more nodules proximal to the first nodule. The most likely
diagnosis is:
1.
2.
3.
4.
Mycobacterium marinum
Sporotrichosis
Aeromonas hydrophilia
Pseudomonas aeruginosa
Nodular Lymphangitis
 Mycobacterium marinum
 Sporotrichosis
 Cutaneous Nocardia
Case History


A 28-year-old man presented to clinic with a 16 cm
erythematous, annular skin lesion on his right flank and flu-like
symptoms. He spent the past 30 days hiking in the mountains.
The most appropriate course of action is:
1. Reassure and don’t give antibiotics
2. Draw serology and treat if positive
3. Give PO Doxycycline for 14-21 days
4. Give IV Ceftriaxone for 14-21 days
Important North American Ticks
Ixodes Female (Adult)
Ixodes Male (Adult)
Ixodes Nymph
Amblyomma Female (Adult)
Dermacentor Female (Adult)
Ornithodoros (Adult)
From: Spach DH, et al. N Engl J Med 1993;329:936-47.
Ixodes scapularis
Blacklegged Tick
Source: CDC Control and Prevention.
Ixodes pacificus
Western Blacklegged Tick
Source: CDC Control and Prevention.
Distribution of Tick Species in Washington State, 1989
Source: Washington Department of Health.
Distribution of Tick Species in Washington State, 1989
Source: Washington Department of Health.
Erythema Migrans Rash
From: Steere AC. N Engl J Med. 2001;345:115-25.
Lyme Disease: General Approach to Treatment


Early Disease (Absence of serious Neurologic/Cardiac)
- Doxycycline
- Amoxicillin
Late Disease or Serious Neurologic/Cardiac Disease
- Ceftriaxone
Case History: Animal Bite

A 33-year-old woman living in Washington State is bitten on her
hand by her cat while trying to break up a fight between her cat
and dog. One day later her wound is red and painful and she
comes to the ER for evaluation. Which of the following is TRUE?
1. Her risk of getting rabies from this cat bite is about 2%
2. Cat bites become infected more often than dog bites
3. Bartonella is the most likely cause of the infection
4. Pseudomonas is the most likely cause of the infection
Microbiology of Infected Cat Bites
From: Talan DA, et al. NEJM 1999;340:85-92.
Case History: Question
• A 29-year-old is bitten by a dog on his hand while trying to break
up a dog fight between 2 pets. This took place in Seattle.
• Which of the following is TRUE regarding dog bites and
infection?
1.
2.
3.
4.
His risk of getting rabies from this dog bite is about 5%
Pseudomonas cani is a common pathogen
Optimal prophylaxis is Amoxicillin
Pasturella is one of the most commonly
isolated organisms
Microbiology of Infected Dog Bites
From: Talan DA, et al. NEJM 1999;340:85-92.
Dog & Cat Bites Wound Infections: Therapy



Therapy (Oral)
- Amoxicillin-CA x 7-14 days
Therapy (Intravenous
- Ampicillin-sulbactam
- Ertapenem
Therapy (Penicillin-Allergic)
- Clindamycin plus Fluoroquinolone
Case History: Skin & Soft Tissue


This 36-year-old man is admitted to intensive care unit 3 days
after suffering a dog bite on his right knee. He has a BP = 85/60,
he has diffuse purpura, and lab studies that show evidence of
DIC. Tragically, he died 6 hours after admission to the ICU.
Which organism most likely caused this infection?
1. Moraxella catarrhalis
2. Pasteurella canis
3. Capnocytophaga canimorus (DF-2)
4. Pseudomonas aeruginosa
Cat Scratch Disease: Bartonella henselae
Cat Scratch Disease: Azithromycin Therapy
From: Bass JW et al. Pediatr Infect Dis 1998;17:447-52.
Questions?