Table of contents
- 1. Introduction
- 2. Notable Cellulitis Pathogens
- 3. Cellulitis
- 4. Necrotizing Fasciitis
- 5. Myonecrosis
- 6. Burns
- 7. Less Severe but Common
- 7.1. Impetigo
- 7.2. Folliculitis
- 7.3. Furunculosis and Carbuncles
- 7.4. Skin Abscesses
- 8. Rare, Indolent
- 9. Animal Bites
- 9.1. Cat Scratch Disease
- 10. Human Bites
- 11. Diabetic Foot Infections
- 12. Why Cellulitis Not Resolving?
.
Introduction
- Two organisms often responsible:
- Group A Streptococcus (GAS) [ B-hemolytic Strep]
- Lymphangitis - "Peau d'orange" appearance of skin
- Staphylococcus aureus
- (including community acquired methicillin-resistant S. aureus) (CA-MRSA)
- Causes abscess or drainage from wound (i.e. previous trauma)
- Group A Streptococcus (GAS) [ B-hemolytic Strep]
- Anatomically
- Superficial:
- Deeper
- furunculosis (hair follicles)
- hidradenitis (sweat glands)
- Cellulitis
- Distinguish from Erysipelas as cellulitis is deeper and not well demarcated.
- Can be due to staph or strep.
- If furuncles, carbuncles or abscesses are present --> usually staph aureus.
- Fascia plane
- Necrotizing faciitis (GAS)
- Thrombosis of vessels in fascia, requires fasciotomy.
- Necrotizing faciitis (GAS)
- Wost case:
- Necrotizing faciitis --> necrotizing myositis (myonecrosis) --> sepsis --> irreversible septic shock
Notable Cellulitis Pathogens
- Most Common
- Staph aureus (furuncles, carbuncles, abscesses, purulent cellulitis)
- Includes MSSA
- Includes MRSA
- v
- Group A Strep (erysipelas, cellulitis)
- Staph aureus (furuncles, carbuncles, abscesses, purulent cellulitis)
- Diagnosis
- 5% positive blood cultures.
- Cultures by punch biopsy or needle aspiration are possible, but not routine.
Cellulitis
- Infection of skin with some extension into subcutaneous tissues.
- On exam:
- need to find portal of entry (tinea pedis, psoriasis, eczema)
- Comment on whether it is well-demarcated
- Comment on crepitus (anaerobic component)
- Causes:
- B-Hemolytic strep (Groups A, B, C, and G)
- S. aureus
- H.infuenzae in kids.
- Special:
- Bite wounds - skin and oropharynx of biter
- Fresh water exposure (Aeromonas hydrophila)
- Seawater exposure (Vibrio vulnificus)
- Diabetic foot ulcer (Polymicrobial)
- Risk factors:
- Venous or lymphatic compromise. (surgery, trauma, CHF)
- Diabetes (peripheral neuropathy and vessel occlusion)
- Chronic Alcoholism (trauma, poor hygenine)
- SPECIAL types of cellulitis:
- Erysipelas:
- Swelling and sharp demarcation
- Almost always GAS (occasionally Group C, G, or B)
- Clostridial cellulitis
- Superficial infeciton of Clostridium perfringens
- Preceded by local trauma or surgery.
- Gas found in skin. (crepitus)
- "Forest fire" progression... most active (red) at the leading edge.
- Do MRI/CT and CK to see if muscle involved
- Non-clostridial anaerobic cellulitis
- Most often in diabetes.
- Distinguish from nec fac and myonecrosis by surgical exploration.
- Other Causes of Cellulitis:
- Aeromonas hydrophila - freshwater lakes, streams, rivers, leeches.
- Vibrio - Salt water, raw seafood.
- Erysipelothrix rhusiopathiae - saltwater marine life (sometimes even freshwater fish).
- Pasteurella multocida - Contact with cats.
- Capnocytophaga canimorsus - Contact with dogs. (or Asplenic patients)
- Bacillus anthracis - bioterrorism. (painless lesions)
- Francisella tularensis - animal (usually cats) or arthropod bites
- Mycobacterium marinum - fresh water, salt water, fish tanks, swimming pools.
- Erysipelas:
- Treatment:
- Mild and early cellulitis (i.e. erysipelas b/c almost always GAS)
- Penicillin
- If suspect S. aureus
- Penicillinase-resistant penicillin (nafcillin, dicloxacillin, cloxacillin?)
- Most commonly:
- Cephalexin, cefazolin, cloxacillin, (ceftriaxone also good coverage, but broad).
- First-gen cephalosporin (cefazolin) covers S. aureus and GAS
- If pen-allergy:
- Use Vancomycin (also covers MRSA)
- For MRSA:
- For Community Acquired MRSA - oral therapies:
- Use septra, tetracyclines, clinda, linezolid.
- NOTE: However, Septra/tetracyclines aren't reliable against strep, so need second agent)
- IV: Use vancomycin, linezolid, daptomycin, etc...
- SEE CA-MRSA SECTION FOR DETAILS
- For Community Acquired MRSA - oral therapies:
- Other measures:
- Elevate, cool, sterile saline dressing to remove exudates. (helps pain too).
- Need 1-2 weeks of therapy.
- Local desquamation can be sen and convalescence.
- Mild and early cellulitis (i.e. erysipelas b/c almost always GAS)
Necrotizing Fasciitis
- Infection that extends beyond the epidermis, dermis, and subcutaneous fat tissues.
- Involvement of the deep fascial plane in abdomen, perineum, and extremities.
- Hard to distinguish from cellulitis or milder infections. Worry if:
- +++ pain! or FEVER, or other systemc effects (tachy etc..)
- Classically (initial): erythematous lesions associated with significant pain and edema.
- Two types: (based on bacteriology and manifestations)
- Type I (often in Diabetics!)
- Polymicrobial w/ G+ and G- aerobic and anerobic. (4-5 usually isolated)
- S.aureus, GAS, E.coli, peptostreptococcus, Clostridium, Prevotella, Porphyromonas, Bacteroides, etc..
- Associated with:
- Diabetes - usually on feet. Suspect nec fasc if systemic symptoms (tachy, leukocytosis, hyperglycemia, acidosis).
- Cervical necrotizing fasciitis - Odontogenic infection after surgery (mucous membranes). In H&N, bacterial penetration into fascia can give:
- "Ludwig's angina" (rapidly expanding inflammation in the submandibular and sublingual spaces after dental surgery).
- Fournier's gangrene - Perineal Fasciitis, penetrates into GI and urethral mucosa, abdominal wall, gluteal muscles (+scrotum and penis in males).
- Polymicrobial w/ G+ and G- aerobic and anerobic. (4-5 usually isolated)
- Type II
- Single organism: classicaly Group A B-hemolytic strep (Streptococcus pyogenes).
- aka "streptococcal gangrene" and "streptococcal toxic shock syndrome".
- Streptococcal gangrene associated with toxic shock syndrome. (50%?).
- Others that can cause similar infections:
- Vibrio (curved gram- rod in warm salty water - gulf of mexico!)
- Typically immunodeficient host: Classically iron overload or cirrhosis.
- Ingestion of raw/uncooked shell fish or broken skin exposed to contaminated sea water.
- Staph aureus
- Staph agalactiae.
- Clostridium perfiringens myonecrosis (aka "Gas Gangrene").
- Vibrio (curved gram- rod in warm salty water - gulf of mexico!)
- MRSA and CA-MRSA are common.
- Single organism: classicaly Group A B-hemolytic strep (Streptococcus pyogenes).
- Type I (often in Diabetics!)
- NOTE: Do serum CK.
- Symptoms:
- Erythematous lesions associated with significant PAIN!!! (typically out of proportion with skin findings), Edema.
- Typically pre-existing skin infection or trauma (i.e. pressure ulcers), typically portal of entry.
- Lesions progress rapidly to form violaceous bullous/gangrenous appearance.
- Palpation: woody induration, crepitus (soft tissue gas).
- Systemic Toxicity:
- Fever
- Hypotension
- Mental status change
- Tachycardia
- Leukocytosis
- Laboratory: multi-organ dysfunction.
- Erythematous lesions associated with significant PAIN!!! (typically out of proportion with skin findings), Edema.
- Labs:
- Evidence of Systemic Inflammation: WBC, ESR, CRP, Serum CK.
- MRI: Finds extent of fascial plane involvement.
- C&S + Stain of wound is helpful.
- Treatment:
- Treatment URGENT!!! (30-70% mortality).
- Surgery if severe pain, sepsis, fever, elevated CK.
- Usually need surgery for debridement and determine extent of necrosis.
- Cultures should be obtained.
- Need surgical re-evaluation 24-48hrs post-op and continued daily.
- Empiric Broad-Spectrum Abx:
- Cover Strep, GN's, Anaerobes, CA-MRSA, MSSA,
- Pip-tazo OR cefepime+metronidazole OR carabapenem (mero/imipenem).
- + Clindamycin (If suspect B-hemolytic Group A Strep or Clostridium is shown to suppress toxin production and improve outcome)
- US Guidelines: + Anti-MRSA Agent (Vancomycin, Daptomycin, Linezolid) is indicated, or if community prevalence is high.
- Pip-tazo OR cefepime+metronidazole OR carabapenem (mero/imipenem).
- Cover Strep, GN's, Anaerobes, CA-MRSA, MSSA,
- Type II Necrotizing Fasciitis
- 2ndary to Group A Strep or Clostridium:
- Penicillin G + Clinamycin indicated.
- 2ndary to Group A Strep or Clostridium:
- Stop Abx when after debridement and clinical improvement evident.
- IVIG: To neutralize exotoxins. Studies conflicting. No definitive recommendations. Some experts recommend in toxic shock or high risk of death
- FLUIDS! and pressors to maintain perfusion pressure.
Myonecrosis
- Uncommon infection of muscle that develops rapidly and is life-threatening.
- Primarily caused by Clostridium perfringens and C. septicum (latter associated with bowel cancer).
- Usually following deep penetrating trauma, but source depends on flora:
- Penetrating trauma --> c. perfringens.
- Bowel -> C. septicum (bowel lesion seeds C. speticum... dies depsite abx treatment and debridement)
- Vagina --> C. sordellii (D&C)
- Myositis other conditions:
- Tropical myositis or pyomyositis
- (S. aureus and others cause primary muscle abscess, common in tropical areas)
- Necrotizing infections by Vibrio vulnificus
- Can involve skin, vascia, muscle. (esp in cirrhosis, raw seafood, living in coastal regions).
- Tropical myositis or pyomyositis
- Pathophysiology
- Initial penetrating trauma introduces organisms into deep tissue. Producing anaerobic acidic environment.
- Rapid tissue desctruction by Clostridium
- alpha-toxin secreted has phospholipase C and sphingomyelinase activity --> induces platelet and PMN aggregation --> blood vessel occlusion and rapid tissue necrosis --> enhances anaerobic environment --> more clostridial growth.
- Alpha-toxin + theta-toxin suppresses cardiac contractility, causes vasodilation --> more tissue hypoperfusion and anaerobic environment.
- Symptoms:
- Skin appears brownish/bronze. --> then purplish red.
- Presence of crepitus locally.
- Signs of systemic sepsis quickly develop. (tachy, low-grade fever, hypotension, shock, multi-organ failure).
- Clostridial bactermia --> extensive hemolysis.
- Gas in soft tissues _> Xray, CT, MRI.
- Treatment: URGENT!
- Removal of necrotic tissue, amputation.
- IV pencillin and clindamycin.
- abx:
- Penicillin, clindamycin, metronidazole, cephalosporins all excellent.
- Typically penicillin + clindamycin used to kill + suspend alpha+theta toxin production.
- abx:
- Hyperbaric O2.
- Outcome often fatal despite treatment.
Burns
- Provides fertile environment for bacterial growth
- Invasive infection can happen:
- Gram+ aerobies (Staph aureus, S. epidermidis, enterococci
- Gram - aerobes (Enterobacter, E. coli Klebsiella, Pseudomonas, and Acinetobacter)
- Burn patients already are febrile, sinus tachycardia, sudden worsening can indicate sepsis.
- Debridement and topical abx are mainstays.
- Give Broad-spectrum if sepsis suspected.
Less Severe but Common
Impetigo
- Superficial, vsiculopustular skin infection.
- Warm, humid conditions (kids), easily spread btwn families.
- GAS and S. aureus.
- Post-strep GN is RARE, but can be prevented with abx.
- Treatment:
- topical, but if multiple lesions: may need systemic.
- Penicillin is good, but many S. aureus resistant. (produce B-lactamases)
- Amox-clav, erythromycin, cephalexin, dicloxacillin and topical mupirocin ointment are effective.
- Preferred: oral erythromycin (250mg or in kids: 12.5 mg/kg q6h x10d).
- OR mupirocin ointment in a polyethylene glycol base locally.
- OR cephalexin (250mg q6h or 500mg BID x10 days).
Folliculitis
- S. aureus is common if carrier. (in nasal opening)
- Pseudomonas if in whirlpools, or pools with inadequate chlorination. "whirlpool folliculitis".
- Abx or steroid therapy --> Candida folliculitis.
- Treatment:
- Treat S. aureus, but pseudomonas and candida can also cause this.
- Systemic abx --> NOT helpful.
- Warm saline compresses, topical antibacterial or antifungal agents.
- To decolonize from nose: Monthly mupirocin ointment to anterior nares bilat twice daily x5 days each month prevents nasal S.aureus colonization.
- If recurrent, and not immunocompromised --> consider P. aeruginosa.
- Complications --> Furunculosis and Carbuncles
Furunculosis and Carbuncles
- Furunculosis --> inflammatory painful nodule surrounds hair follicle. (after folliculitis).
- Carbuncle --> Larger subcutaneous abscess that progreses from furuncle. Often need drainage.
- Both caused by S. aureus, MRSA is concern (prisons, hospitals, contact sports, etc.)
- Usually in areas with friction and perspiration (back of neck, face, axillae, buttocks).
- Systemic sx are uncommon. Fever is rare.
- Treatment:
- warm compresses to promote spontaneous drainage.
- If fever --> Dicloxacillin (cloxacillin?).
- If pen-allergic --> cephalexin or clindamycin.
- If MRSA suspected:
- TMP-SMX
- Surgically drain if do not drain spontaneously.
- Seeds hematogenously.. may need to prophylax against endocarditis.
- If recurrent:
- Prophylaxis:
- Chlorhexidine
- Personal hygeine.
- Nasal muprocin to decolonize S. aureus.
- Prophylatic abx.
- Prophylaxis:
- Dangerous!:
- On face --> cavernous sinus infection.
- Bacteremia can occur if manipulated.
Skin Abscesses
- S.aureus most common
- Tx same as Furuncles / Carbuncles.
- Consider oral clindamycin if anaerobes are involved.
- If recurrent:
- R/O D/M
- Neutrophil dysfunction
- Immunoglobulin E syndrome.
- May need to prophylax for endocarditis before I&D.
Rare, Indolent
- Often chronic skin infections, non-responsive to abx.
- Water-pathogens:
- Erysipelothrix --> fisherman cut fingure on fish spine. (penicillin, clinda, cipro)
- Mycobacterium marinum (minocycline or clarithromycin). (acquariums, fresh/salt water)
- Plants/soil
- Sporotrichosis (itraconazole) - gardeners cut finger on bush thorn.
- Nocardiosis (TMP-SMX, azole).
- Tetanus
- human tetanus immunoglobulin.
- tetanus toxoid vaccine
- IV metronidazole
- benzos and pancuronium, or intrathecal baclofen to control spasms.
- Short acting B-blockers, VI magnesium sulfate, vasopressors for autonomic instability.
- Intubation and tracheostomy is often required.
- PREVENT!
- vaccine tetanus toxoid q10y.
- Booster q5y or so if contaminated wound.
- Patients high risk may need tetanus Ig.
Animal Bites
- Infection of bites due to oral flora of the animal.
- Infection after dog + cat bites due to mix of aerobic and anaerobic organisms.
- DOG bites are less likely to get infected than cat bites.
- Most commonly with pet animal bites: Pasteurella (50% of cat bites and 70% of dog bites) - GN coccobacilli.
- P. canis in dog bites
- P. multocida in cat bites.
- Other organisms cultured form bite wounds:
- S. aureus
- Streptococci (staph+strep in 40% of bite wounds)
- Capnocytophaga canimorsus
- Gram neg rod can cause overwhelming sepsis (mostly in asplenia).
- Anaerobes
- Most commonly with pet animal bites: Pasteurella (50% of cat bites and 70% of dog bites) - GN coccobacilli.
- Result infections are often polymicrobial
- Must irrigate and debride the wound.
- DO NOT CLOSE THE WOULD INITIALLY
- Wound irrigation + cleaning.
- If animal is unprovoked:
- Tetanus prophylaxis
- Rabies prophylaxis (vaccine/IgG)
- Capture animal and observe for rabies.
- Prophylaxis is recommended:
- Recommended for:
- Immunocompromised
- Wound on hands or near joint/bone.
- Moderate-severe wounds.
- Crush injuries
- Wounds associated with edema.
- Oral amox-clav (875 mg bid x3-5 days)
- If Penicillin allergic:
- Fluroquinolone (i.e. cipro 400mg IV then 500mg PO BID) or doxycycline or TMP/SMX
- + ADD clindamycin (900mg IV + 300mg PO Q6h) for anaerobic coverage.
- Fluroquinolone (i.e. cipro 400mg IV then 500mg PO BID) or doxycycline or TMP/SMX
- If Penicillin allergic:
- In children: clinda + trimethoprim-sulfamethoxazole recommended.
- Recommended for:
- Treatment: (IF infected)
- All infected dog/cat bite wounds require antimicrobial therapy
- Same oral regimen as prophyalxis, but longer (10-28days)
- Do not use 1st gen cephalo, dicloxacillin, erythromycin b/c organisms resistant. (i.e. P. multocida)
- Hospitalize if:
- Severe/deep infections
- Nerve/tendon/crush injuries
- Infected hand bites.
- If hospitalized use IV:
- pip-tazo (other B-lac + inhibitor), cefoxitin, carbapenem.
- If Pen-allergic, use fluoroquinolone + clindamycin.
- Consider vancomycin if MRSA suspected.
- pip-tazo (other B-lac + inhibitor), cefoxitin, carbapenem.
- Duration of therapy:
- <2w treatment
- 3-4w if joint infection
- 4-6w if bone infection.
-
Cat Scratch Disease
- Occurs in immunocompetent children and young adult following innoculation with:
- Bartonella henselae (Gram neg)
- Pustular papule or erythema at the site days to weeks after scratch/bite.
- + tender regional lymphadenopathy, takes months to resolve.
- Diagnosis:
- Clinically
- Can do laboratory dx with culture/serology/histoy/PCR.
- Treatment:
- Self-limited
- Some recommend short course of abx (usually azithromycin).
- Occurs in immunocompetent children and young adult following innoculation with:
Human Bites
- Infections usually polymicrobial
- Categorized by:
- Self-inflicted (thumb sucking, nail biting)
- Occlusional (confrontation)
- Clenched-fist injuries
- Organisms:
- S. viridans
- S. aureus
- Anaerobes:
- Eikenella corrodens (concern b/c resistant to oxacillin, nafcillin, clinda, metronid. and also many cephalosporins)
- Bacteroides sp.
- Fusobacterium sp.
- Peptostreptococci.
- Prophylaxis
- All human bite wounds require antimicrobial prophylaxis
- with amox-clav (3-5days)
- Avoid oxacillin, nafcillin, clindamycin, metronid. and many cephalosporins.
- Clenched-fist injuries (prone to deeper infections of tendons/joints/bones)
- Xray, consult hand surgeon, and possible hospitalizations.
- Often also think about:
- HIV, Syphilis, HSV, HepB/C
- Treatment with ampicillin-sulbactam IV, icarcillin-clavulanate, or cefoxitin.
- Duration based on severity of injury - joints, bones, tendons.
Diabetic Foot Infections
- Diabetic foot infections common due to neuropathy, impaired vascular supply, immunodeficiency of diabetes.
- Typically come after trauma.
- Categorized as:
- Mild
- Caused by staph and strep.
- Symtoms: purulence or inflammation (pain, tenderness, warmth, erythema, induration)
- Cellulitis ≤2cm around the ulcer (no deep involvement)
- NO systemic findings
- Moderate
- Cellulitis >2cm around the ulcer, gangrene, lymphangitic spread, deep tissue abscess, deep tissue spread (muscle, tendon, bone)
- Severe
- Limb threatening
- Systemic toxicity (fever, tachycardia, hypotension, renal insufficiency, mental status, leukocytosis).
- Polymicrobial: strep, staph, enteric gram negatives, pseudomonas, anaerobes.
- Mild
- Physical Exam:
- RULE OUT:
- Arterial insufficiency
- Osteomyelitis
- Bone changes related to neuropathy and charcot changes can mimic osteomyelitis.
- RULE OUT:
- Imaging (R/O Osteomyelitis):
- Xrays are insensitive for osteomyelitis (sens 0.54), can show underlying gas or foreign bodies.
- MRI is much better for osteomyelitis and abscesses.
- IF cannot do MRI, can do bone scan.
- Labs:
- Evaluate for systemic toxicity
- Can get cultures from aspiration or deep tissue cultures from surgery.
- Do not swab (misleading, AVOID)
- Treatment:
- NOT ALL ULCERS ARE INFECTED
- Some don't have purulence, inflammation.
- Do not need antibiotics.
- Mild + Moderate:
- Abx - aerobic staph and strep coverage.
- Severe Limb Threatening
- Surgical Evaluation
- + cultures
- Initial broad spectrum abx.
- Surgical Evaluation
- Rule out Osteomylitis:
- Challenging: bone changes related to neuropathy and charcot changes (repeated trauma) mimic OM.
- Typically requires MRI (occult) or bone scan.
- OM becomes apparent over time as wound drainage recurs after healing or ulcer closure.
- ESR and CRP - insufficient evidence.
- High likelihood if can touch bone through ulcer with hard object.
- NOTE: Probe to bone test (ADA, Diabetes Care, 2007): PPV 0.57, and NPV 0.98 (low positive predictive valuve, but good for ruling out).
- Duration of therapy:
- No Osteomyelitis: 7-10days.
- If Osteomyelitis: 6 weeks.
- Wound care (clensing, debridement, offloading foot pressure).. essential!
- Involve podiatrists and wound care specialists.
- Rule out arterial insufficiency
- Ankle-Brachial Index!
- Revascularization may help.
- Other therapies lacking evidence:
- Hyperbaric oxygen, maggots, vacuum assisted dressing.
- NOT ALL ULCERS ARE INFECTED
Why Cellulitis Not Resolving?
- Consider:
- Not right drug for bug.
- Drug does not get to bug
- Complication (Abscess etc..)
- Wrong diagnosis (Stasis dermatitis)
- Impatient MD
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