Cellulitis and Soft Tissue Infections

Sally Williams MD

Cellulitis: A very common infection

25 cases per 1000 patient years

More common in men, obese patients

60% occurs in the lower extremities

74% handled as outpatients

82% of patients have just a single episode

High cause of hospital readmissions

Cellulitis: definition

A nonspecific term that includes a large collection of skin & soft tissue infections

Can include:– Erysipelas (the most common cellulitis)

– Cellulitis associated with abscesses

– Gangrenous cellulitis

– Secondary infection of pre-existing skin lesions

– Cutaneous involvement of systemic illness

Normal Skin Structure

Locations of Skin Infections

Impetigo and ecthyma: upper epidermis

Erysipelas and cellulitis: lower epidermis and dermis

Carbuncles, furuncles, “boils” : deep dermis and hair follicles

Necrotizing fasciitis: deep, next to muscle

Microbiology of Cellulitis

The vast majority are strep and staph

More unusual etiologies:– Cat bite: Pasteurella

– Dog bite: Capnocytophaga (splenectomized)

– Rat bite: Streptobacillus

– Fresh water: Aeromonas

– Salt water:Vibrio and Mycobacterium marinum

– Hot tubs: Pseudomonas

Classic hot tub folliculitis

Mix and Match

Impetigo

Very common skin infection in kids Has appearance of “honey colored crusts”,

often on face Etiology is always staph or strep Treat with topical bactroban or oral abx Bullous impetigo is always staph, forms

vesicles and bullae Impetigo quite infectious!

Impetigo

Erysipelas: Clinical Features

Often of rapid onset

Etiology is always streptococcal

Often preceded by fevers, chills and groin pain (for lower extremity cellulitis)

Often blisters after a few days

Usually has lymphangitic streaking

Almost always worsens in appearance before improving on antibiotics

Classic Leg Cellulitis

Facial Cellulitis

Erysipelas continued

Risk factors for erysipelas/strep cellulitis:– Leg edema

– Previous leg surgery

– Obesity

– Previous breast surgery (for arm and breast cellulitis)

– Tinea pedis (NOT onychomycosis)

– Uncontrolled diabetes

Natural History of Erysipelas

Is almost always preceded by fevers, chills, and rapid increase in erythema

ALWAYS gets “worse” before better– Will extend outside drawn “borders”

Almost always has fever and elevated wbc

Can take WEEKS to get better if has underlying edema, history of surgery etc

Will often blister

Is this Cellulitis??

Is this Cellulitis?

Rule #1

There is no entity of “BILATERAL lower extremity cellulitis”.

These are usually all chronic stasis dermatitis

True cellulitis almost always has:

– 1. Elevated wbc

– 2. Erythema above the knee

– 3. Fever, and often preceding chills

– 4. Often “patches” of cellulitis on upper thigh

Rule #2: Please do not culture this

Wound Cultures

Never culture a chronic open wound– The wounds will ALWAYS be colonized with

multiple bacteria– A wound without PMNs on gram stain is probably

not an infected wound– Countless unnecessary courses of antibiotics are

used, predisposing pts to C difficile

If you can unroof an abscess or express pus from something then culture that

Rule #3: Vancomycin not needed for cellulitis without boil

Classic cellulitis is streptococcal

Strep releases a streptozyme to dissolve layer underneath the skin, causing rapid spread.– Multiple different strep species may cause

cellulitis (A,B,C,F,G)

– Strep almost always causes lymphangiitis

Staph cellulitis is almost always associated with a boil or abscess

Staph skin boils

Cellulitis continued

Treatment of non-boil, non-nec fasc cellulitis is strep targeted- Rx cefazolin or ceftriaxone

As soon as they let the leg down will get bigger, redder, hotter – this is NOT treatment failure, just dependent edema.

We need to prepare patients that the leg may look abnormal for months in some cases

History of MRSA irrelevant if looks streptococcal– Please do NOT use vancomycin for diffuse cellulitis

Cellulitis Treatment

Most heavy weight people “fail” oral antibiotics due to insufficient blood levels – may need a course of iv antibiotics or high bioavailability oral antibiotic.

“Failing” keflex is not a reason to use vancomycin –they just need iv cefazolin

Strep itself is easy to kill but the infection causes a lot of “leftover damage” as the lymph system is often damaged. We have to prepare patients for slow improvement

Summary: Leg Cellulitis

Occurs most commonly in the obese or persons with a history of surgery in that leg

Warn them of “worsening” when they start ambulating, leg will get redder, hotter

If you use po antibiotic, need very high doses, e.g. 1-1.5g cephalexin qid

If they truly “failed” high dose keflex could consider oral levoflox, has high blood levels

MRSA: Not a spider bite(courtesy of GiantMicrobes.com)

MRSA Epidemiology

First described in 1961

Previously hospital associated, now widely community acquired since 2002

Most C.A. MRSA strains are US 300 and carry the PVL (panton valentine leukocidin) gene, causes necrosis

C.A. most commonly skin/soft tissue infections, less likely bacteremia

Staphylococcal Cellulitis & BoilsRisk Factors

Young age

Immunocompromised

Contact sports

Crowded conditions

Sharing towels, sheets etc

Prior antibiotics, especially quinolones

Antibiotics for Staph skin boils-do they help?

Randomized studies are conflicting

Many studies show no benefit to antibiotics after incision and drainage

The studies that did show a benefit related a small one with using TMP-S + I&D.

Drainage is likely 95% of the battle-if the pt has extensive induration oral Rx may be helpful, especially if >2 cm.

Antibiotic treatment for MRSA

Vancomycin for the hospitalized patient, Daptomycin also useful but expensive

Clindamycin resistance up to 33%

Bactrim is still sensitive >90% of the time

Doxycyline resistance actually quite low

Linezolid effective, but has rare drug interactions– Serotonin syndrome <.1%, still black box warning

Dalbavancin/Oritavancin: likely to not be used due to >$1000 per dose of antibiotic

Does antibacterial soap help?

Antibacterial Soap? You Can Skip It, Use Plain Soap and Water (FDA November 2017)

Most contain triclosan, a pesticide– No proven efficacy

– Potential to cause antibiotic resistance

– Potential to affect hormones

Hand sanitizers ARE effective

Recurrent skin lesions

Most common in young overweight women

Essentially acquisition is bad luck, can be very difficult to eradicate

Nasal mupiricin for household sometimes effective, with mass washing

For severe cases Bactrim suppression for a few months is an option

Necrotizing Fasciitis

Uncommon severe infection

Etiologies may be:– Streptococcal (most common)

– Polymicrobial –usually associated with gut flora (e.g. perirectal abscess, Fourniers) or trauma

– Staphylococcal –usually post op, needs to be differentiated from necrotizing staph soft tissue infection which is very common.

Strep necrotizing fasciitis

Clinical Picture of Necrotizing Fasciitis

These patients are very ill – febrile, hypotensive, tachycardic, delerious

Pain out of proportion to exam

Cutaneous anesthesia

Very rapid spread

May have skin bullae (often black), ecchymoses, usually edema

Example of Leg Nec Fasc

Necrotizing Fasciitis

WBC almost always very high or very low

Cr usually about 2, pt often in toxic shock

Nec fasc is a SURGICAL EMERGENCY

Antibiotics are targeted toward strep, staph or polymicrobic- Vanco + Piptazo

Clindamycin is added as inhibits toxin production, but surgery is life saving

How does Necrotizing fasciitis/ toxic shock happen?

BAD LUCK

It requires a toxin producing strain of strep (rare) often in the setting of uncontrolled DM

AND a lack of immunity to the toxin (also rare)

IVIG is often used with toxic shock to give patient a large “antibody load” -someone in the large pool of donors likely has an antibody to the toxin

Summary: Skin Infections

Cellulitis is common and is usually strep

Most cellulitis gets worse before better

Boils are almost always staph/MRSA and need to be drained to achieve cure

Chronic stasis dermatitis is incredibly common and should not be mistaken for cellulitis

Nec fasciitis is rare and pts are very ill

IDSA SSTI guidelines

Antibiotic humor

Superbugs coming…