Skin and Soft Tissue (SST) Infections Michael J. Tan, MD, FACP, FIDSA Associate Professor of Internal Medicine Northeastern Ohio Universities Colleges.

Skin and Soft Tissue (SST) Infections

Michael J. Tan, MD, FACP, FIDSAAssociate Professor of Internal Medicine

Northeastern Ohio Universities Colleges of Medicine and Pharmacy

Summa Health System, Akron, OH

A 47 year old known IV drug abuser presents to the ED with a painful swollen arm of 8 hours duration. Swelling has extended from the antecubital area to the entire arm in 2 hours. Which of the following is appropriate therapy?

A. Initiate vancomycin alone B. Call the surgeon for immediate

debridement C. Treat with IVIG alone D. Aspirate the antecubital area E. None of these is appropriate

Objectives Review types of common skin and soft tissue

infections Recite common pathogens associated with

these infections Review diabetic foot infections Understand treatment modalities and

antimicrobials used for these infections

Bacterial Skin and Soft Tissues Infections Primary Pyoderma

Impetigo, erysipelas, folliculitis, carbuncles Infections secondary to pre-existing conditions

Surgical wounds, trauma, bites, decubitus infections, diabetic foot infections

Necrotizing infections Polymicrobial Monomicrobial (Gp A. Strep; Clostridium)

Bacterial SST Infections General Approach to therapy

Antimicrobial therapy Directed against likely pathogens Common organisms Specific pathogens based on epidemiology Emerging antimicrobial resistance

Community-Onset MRSA, macrolide resistant S pyogenes Healthcare-associated pathogens

Surgical Incision and drainage, debridement, excision

Bacterial SST Infections Practice Guidelines for the Diagnosis and

Management of Skin and Soft-Tissue Infections

Infectious Diseases Society of America (IDSA)

IDSA Guidelines. Stevens D et al. Clin Infect Dis 2005;42:1379-406

Bacterial SST Infections General Considerations

Diverse Etiologies Depends on epidemiological setting

Immune status Geographical locale Trauma or Surgery Prior antimicrobials (resistance) Lifestyle Animal exposure


Bacterial SST Infections Management

Diagnosis Clinical findings Biopsy

Assessment of severity of infection Therapy

Antimicrobial therapy Surgical debridement/excision


Bacterial SST Infections Severity of Infection

Evaluate for systemic toxicity Fever, tachycardia, hypotension Consider need for hospitalization if:

Hypotension, increased creatinine or CPK, decreased bicarbonate (acidosis), CBC with left shift

Severe, deep infection, or necrotic infection


Mimics of Material Skin and Soft Tissue Infections Acute allergic reaction

Contact dermatitis Toxin (eg chemical) Trauma Thermal reaction (hyper-, hypo-) Acute gout

Common Skin Infections (Primary Pyoderma)

Infection Common Pathogens

Folliculitis Staphylococcus aureus

Whirlpool folliculitis Pseudomonas aeruginosa (usually self-limited)

Abscess Staphylococcus aureus

Impetigo Streptococcus pyogenes, and Staphylococcus aureus

Erysipelas Staphylococcus aureus, and Streptococcus pyogenes

Cellulitis Streptococcus pyogenes, and Staphylococcus aureus

Lymphangitis Streptococcus pyogenes

Community-associated MRSA

65 y/o female with a boil unresponsive to 3 days of cephalexin

Photo courtesy of T. File MD

CDC Definition of CA-MRSA Diagnosis of MRSA made in the outpatient setting

or by a culture positive for MRSA within 48h of hospital admission

Patient has no medical history of MRSA colonization or infection

Patient has no medical history in the past year of: Hospitalization Admission to a nursing home, skilled nursing facility

or hospice Dialysis Surgery

The patient has no indwelling catheters or medical devices that pass through the skin

www.cdc.gov

Community-Associated (CA) MRSA Increasing cause of community skin infections Genotypically and phenotypically unique from

nosocomial MRSA Less resistant to non-beta-lactam agents Often susceptible to TMP-SMX, clinda, tetracyclines,

+/- fluoroquinolones Panton-Valentine leukocidin (PVL) – virulence factor

Risk Factors Athletes, inmates, military recruits, men who have

sex with men, injection drug user, prior antibiotic use Increases need to culture.

18 y/o male treated with amox/clav for ‘spider’ bite at local urgent care center.

3/21/05 3/22/05

Photos courtesy of T. File MD

Pyoderma-Antimicrobial Therapy S. pyogenes

Beta-lactams; Others: macrolides (resistance 5-10%), clindamycin, doxycycline, minocycline

S. aureus MSSA: antistaphylococcal penicillins (ie

dicloxacillin, nafcillin, oxacillin); cephalosporins; clindamycin; macrolides; doxycycline, minocycline, TMP-SMX

MRSA Hospital acquired: Vancomycin, linezolid, daptomycin Community-associated: Trimethoprim-

sulfamethoxazole; doxycycline/minocycline; clindamycin (if “D Test” negative)

Modified from IDSA Guidelines. Stevens D et al. Clin Infect Dis 2005;42:1379-406

INFECTIONS ASSOCIATED WITH UNDERLYING CONDTIONS

InfectionsPost Op wound infections Lower extremity cellulitisDiabetic foot ulcersDecubitus ulcersBite wound infectionsPost Trauma infectionsPerforated bowel


Bacteriology: SST Infections associated with underlying conditions Gram positive cocci

S aureus MSSA MRSA (Hospital-acquired; community-acquired) VIRSA, VRSA

Streptococcal spp (including GBS and other spp) Enterococci (VRE)

Gram negative bacilli Enterobacteriaciae Pseudomonas sp

Anaerobes

What can you expect?

superficial

Deep

Gram Positives

GNAnaerobes

ANTIMICROBIAL ACTIVITY

Agents Staph**/Strep GNB AnaerobesNafcillin/Cefazolin + 0 0Cefoxitin/ + +/-* + CefotetanAmp/sulb (amox/clav) + +/-*

+Pip/tazo; Ticar/C + + +Ertapenem + +* +Imipenem/Mero + + +FQ + Clinda (metronid) + + +

* not for Pseudomonas** If MRSA: Vancomycin (>99%), Linezolid (>99%), Daptomycin

(>99%), [Others: Trim/sulf (60-80%), Minocin (90%),

Diabetic Foot Infections

62 y/o postman with fever and draining foot ulcerPhoto courtesy of T. File MD

Diabetic Foot Infections Predisposing Factors

Peripheral Neuropathy Maldistribution of weight (trophic ulcers) Failure to sense problems (corns, calluses)

Vascular insufficiency Bacterial etiology

Early, superficial – Strep, Staph Late, deep – Mixed

Therapy – Surgery and antimicrobial agents Multi-disciplinary approach

Post-Op 6 Weeks later


Effect of Early Surgery on SubsequentAbove Ankle Amputation (Tan JS et al. Clin Infect Dis 1996;23:286-291)

Effect of Early Surgery on SubsequentAbove Ankle Amputation (Tan JS et al. Clin Infect Dis 1996;23:286-291)

Other Specific Skin InfectionsEpidemiology Common Pathgen(s) Therapy

Cat/Dog Bites P. multocida;

Capnocytophaga

Amox/clav (Doxy; FQ or SXT + Clinda)

Human bites Mixed flora Hand Surgeon; ATB as above

Fresh water injury Aeromonas FQ; Broad Spectrum Beta-lactam

Salt water injury

(warm)

Vibrio vulnificus FQ; Ceftazidime

Meat-packing Erysipelothrix Penicillin

Cat scratch Bartonella Azithromycin

IDSA Guidelines. Stevens D. et al. Clin Infect Dis 2005; 42:1379-406

Necrotizing Skin Infections Characteristics

Often perineal or lower extremity (especially for mixed infections)

Abnormal inflammatory response (less “purulent”) Often rapidly spreading Putrid discharge (what organisms?)/crepitance

often present Associated with

DM Vascular disease Trauma (bites included) Surgery

Necrotizing Skin Infections Pathophysiology

Mixed aerobic/anaerobic infection Synergistic infection Presence of facultative organisms creates better

anaerobic environment for anaerobes Virulence factors of one organism assists another

organism (anti-phagocytic effect of B. fragilis capsule) Growth factors

Monomicrobial (eg Strep, Staph, clostridia) Toxins Enzymes

S. aureus Polymicroibal

Necrotizing Skin Infections Manifestations

Tissue necrosis, spreading, bullae, severe pain, pain out of proportion, pain then no pain.

Often severe intensity of illness Requires EXPEDITIOUS SURGERY.

Several anatomical syndromes Eg necrotizing fasciitis; gas gangrene others Cannot easily differentiate syndromes on basis of initial

clinical presentation Initial approach is similar: Early surgery and antibiotics

Microbiology Mixed anaerobes/aerobes Monomicrobial

Streptococcus pyogenes Staphylococcus aureus Clostridia sp (perfringens most common)

Necrotizing Fasciitis Microbiology: 2 Types

Type 1- polymicrobial (aerobic/anaerobic) ie diabetic foot infection, decubitus infection, bite wounds

Type 2 – S pyogenes (Strep toxic shock syndrome) Characteristics

Erythema and swelling, bullae, gangrene Type 1 may have a foul odor (mixed infection) Initially severe pain, but as tissue necrosis

progresses, the pain may disappear

Diabetic woman with rapidly spreading gangrenous infection



Infection 8 hours after amputation


Gas Gangrene due to C. perfringens


Clostridial skin infections Clostridial cellulitis

Infection limited to the dermis and epidermis Abundance of gas, usually not systemically ill

Clostridial myonecrosis (classic gas gangrene) Rapid onset of necrosis, pain, and toxic state Usually associated with devitalized tissue (trauma,

surgery, peripheral vascular disease) Clostridial toxins (alpha toxin)

Lyses blood cells and causes tissue destruction Therapy – Immediate surgery, antibiotics +/-

hyperbaric O2? Clostridium septicum

Consider adenoCA of Colon, leukemia.

Clostridial cellulitis


S pyogenes Necrotizing Fasciitis Increasing frequency over past decade

Result of specific toxins-Streptococcal pyrogenic exotoxins (SPE). Causes release of cytokines (TNF), which can mediate fever, shock and tissue injury

Most cases sporadic (occasional secondary spread); often in normal host

Bacteremia ~50% Mortality 20-40% Therapy

Rapid surgery Antibiotics


Necrotizing Fasciitis (NF) due to CA-MRSA 14 cases of NF due to CA-MRSA from one center

Represented 29% of all cases of NF 71% men; mean age 43; 40% bacteremic 10/14 with coexisting medical problems

IVDU, DM, Hep C, Cancer, HIV Prior MRSA Specimens showed few or no WBCs on gram

stain All susceptible to Vanc, TMP-SMX, clinda All had complicated ICU courses; deaths

NEJM 2005;352:1445-1453

Clues Suggesting NF vs. Cellulitis Pain more severe than expected (followed by

anesthesia) Rapidly spreading swelling and inflammation Bullae (but can be seen with cellulitis as well) Necrosis Toxic shock syndrome Elevated CK Risks: Varicella, NSAIDs

Necrotizing Fasciitis Diagnossis

CT/MRI Edema along fascia

Direct inspection (surgical) Swollen, dully gray, string Thin exudate, not pus Tissue easily dissected Biopsy


Necrotizing Infections-Therapeutic approach Surgical debridement/excision Antimicrobial therapy

Directed initially against mixed aerobic/anaerobic flora Ampicillin/sulbactam or Piperacillin/tazobactam PLUS

clindamycin (theoretically to inhibit protein synthesis and supress bacterial toxin) PLUS ciprofloxacin;

Other regimens: imipenem, meropenem, ertapenem, clindamycin PLUS aminoglycoside or fluoroquinolone

Recommendation to use IVIG cannot be made with certainty (Kaul et al. Clin Infect Dis 1999; Norrby-Teglund et al.

Curr Rrep Inf Dis, 2001: Low et al, ICAAC 2003)

DSA Guidelines. Stevens D et al. Clin Infect Dis 2005;42:1379-406

Bacterial SST Infections General approach to therapy

Surgical I&D, debridement, excision Antimicrobial therapy

Directed against likely pathogens Common organisms Specific pathogens based on epidemiology Emerging antimicrobial resistance

Community-onset MRSA; macrolide Res S pyogenes Health0care associated pathogens

Skin and Soft Tissue (SST) Infections Michael J. Tan, MD, FACP, FIDSA Associate Professor of Internal Medicine Northeastern Ohio Universities Colleges.

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