Skin and soft tissue infections (SSTI) (IDSA 2014)

Introduction

Exposure history is important
Physical examination for diagnosis
History must include
- Immune status
- Geographic locales
- Travel history
- Recent trauma and surgeries
- Recent antibiotics exposure
- Lifestyle
- Hobbies
- Animal exposures

Impetigo and Ecthyma

Background

Impetigo is a superficial infection of the epidermis (?)
Bullous impetigo is caused by Staph. aureus strains that produce a toxin that cleaves the dermal-epidermal junction
Non-bullous impetigo can be caused by Staph. aureus and Group A Strep
Ecthyma is a deeper infection, and heals with scarring

Organisms

Management

Gram stain and culture of any pus, if possible
Superficial and localized infections can be treated with topical mupirocin BID x5d
Otherwise, treat with dicloxacillin or cephalexin x7d
Can narrow if cultures grow Group A Strep alone
If MRSA, treat with doxycycline, clindamycin, or Septra

Purulent SSTIs

Includes abscesses, furuncles, carbuncles, and inflamed epidermoid cysts

Abscesses and inflamed epidermoid cysts

Epidermoid cysts contain skin flora in keratinous material and are not necessarily infected, but can become inflamed if the capsule ruptures
Organisms: Staph. aureus and skin flora
Management
- Incision and drainage; no packing (increases pain without changing outcomes)
- Add antibiotics if impaired immunity or systemic symptoms

Furuncles and carbuncles

Furuncles are small abscesses of hair follicles
Carbuncles involve many adjacent follicles
Organisms: almost exclusively Staph. aureus
Management
- Often drain spontaneously with warm wet compresses
- If large enough, can incise and drain
- No need for antibiotics unless systemic symptoms

Recurrent abscesses (at the same site)

Differential diagnosis includes foreign body, hidradenitis suppuritiva, and pilonidal cysts
Organisms: excluding above causes, often Staph. aureus
Management
- Treat underlying cause, if possible
- Can try MRSA decolonization with
  - Intranasal mupirocin BID for 5 days each month, with daily chlorhexadine washes
  - Clindamycin 150mg for 3 months
If present since childhood, rule out a neutrophil disorder

Erysipelas and Cellulitis

Background

Infections of the dermis and subcutaneous fat, characterized by diffuse areas of erythema, edema, and tenderness
Specifically *not *purulent; if there's an abscess, then it's an abscess with surrounding erythema (not with surrounding cellulitis)
Erysipelas refers to either (1) a superficial infection of the upper dermis, or (2) a cellulitis of the face, or (3) a synonym of cellulitis
On examination, there can also be lymphangitis, peau d'orange, vesicles, bullae, or hemorrhagic lesions
Occasionally, the fever can precede the skin findings
Risk factors include: obesity, trauma, surgery, prior cellulitis, venous insufficiency, lymphedema

Organisms

Group A Strep
Other streptococci
Staph. aureus

Management

Blood cultures are unnecessary unless there is something unusual, immunosuppression, or sepsis
Treat with an antistreptococcal antibiotic, such as penicillin, amoxicillin, dicloxacillin, cephalexin, or clindamycin for 5 days
No need to empirically cover MRSA
Treat any underlying skin breach, including macerated skin between the toes
Can use prednisone (if no diabetes) or NSAIDs to help symptoms resolve faster

Recurrent infections

Identify and treat predisponsing conditions: edema, obesity, eczema, venous insufficiency, and toe web abnormalities
Prophylactic antibiotics can be considered in patients who have 3-4 episodes per year despite treating their predisposing factors
- Oral penicillin or sythromycin bid for 4 to 52 weeks
- IM benzathine penicillin every 2-4 weeks
Continue prophylaxis until the predisposing factors resolve

Surgical site infections

Background

Three classes
- Superficial incisional SSI: involve only the subcutaneous space, occurs within 30 days, and has one of:
  - Purulent drainage
  - Positive culture of aseptically-obtained fluid or tissue
  - Local cellulitis after the wound has been opened
  - Expert opinion suggests SSI
- Deep incisional SSI: involves fascia and mucle, within 30 days (or 1 year if prosthesis inserted), and same as above
- Organ/space SSI: same as deep SSI but may involve organs and deep space, e.g. peritonitis, empyema, and joint infections

Organisms

Depends in part on site of incision, but generally S. aureus and streptococcal species
Axillary incisions may have more gram-negative organisms, and paerineal incisions have more gram-negatives and anaerobes

Management

Open the incision and evacuate the cavity
Drainage alone if <5cm erythema and minimal systemic symptoms
For some reason, IDSA seems to suggests tazo or mero as first-line; possibly just for gastrointestinal and genitourinary incisions

Necrotizing Fasciitis

Background

Involve the fascial or muscle compartments and are life-threatening
Usually develop from initial skin trauma, which can be trivial including insect bites
Presents as a rapidly-progressing cellulitis, with systemic symptoms and pain out of proportion to findings
May have wooden-hard induration, and if there is an open wound, you can easily dissect the fascial planes
Risk factors include diabetes

Organisms

Monomicrobial: Streptococcus pyogenes, Staphylococcus aureus, Vibrio vulnificus, Aeromonas hydrophila, and anaerobic streptococci (Cutibacterium)
Polymicrobial: numerous aerobes and anaerobes, mostly arising from the bowel or genitourinary tract

Management

CT or MRI is not diagnostic
Surgical exploration for diagnosis and deep tissue cultures
Surgical intervention urgently, and daily until source control is achieved
Treat with antibiotics until source control achieved and afebrile for 48-72 hours
Empiric antibiotics should cover gram-positives, gram-negatives, and anaerobes
Group A streptococcal toxic shock syndrome should be treated with clindamycin and penicillin
- The utility of IVIg is unclear; small RCT suggests not

Fournier gangrene

Variant involving the scrotum and penis or vulva, where a perianal or retroperitoneal infection has spread to the genitalia
Testes, glans, and spermatic cord are typically spared
Mostly mixed aerobes and anaerobes

Pyomyositis

Background

Pus within an individual muscle group, often associated with tropical climates
Risk factors include tropical climates, HIV, diabetes
May have a firm woody feel
CK often normal

Organisms

Staph. aureus in 90%
Group A Strep and gram-negative enterics also possible

Investigations

MRI establishes the diagnosis, though CT and US are useful
Get blood cultures (positive in 5-30%)
Repeat imaging if persistently bacteremic in order to find other infections

Management

Needs incision and drainage
Vancomycin is appropriate empiric therapy
Add Gram-negative coverage if immunocompromised or open trauma
Cefazolin for oxacillin for MSSA
Duration is with IV until better and not bacteremic, then oral to complete 2-3 weeks

Gas Gangrene and Myonecrosis

Background

Increasing pain at the injury site within 24 hours
Skin starts pale, then bronze, then purplish-red, tenderness at the site, followed by reddish-blue bullae
Septic

Organisms

Clostridium perfringens, C. novyi, C. histolyticum, and C. septicum
C. perfringens most commonly associated with trauma-associated gangrene, and C. septicum with spontaneous gangrene in neutropenic patients or those with GI malignancy

Management

Many organisms produce gas, so needs broad empiric coverage with pip/tazo, amp/sulb, or carbapenem
Penicillin + clindamycin is the recommended treatment
Unclear role for hyperbaric oxygen

Animal Bites

Prophylaxis

Unclear benefit of prophylaxis, but suggest 3-5 days of amox/clav to cover aerobes and anaerobes in high-risk patients
- Immunocompromised
- Asplenic
- Advanced liver disease
- Preexisting edema in the affected area
- Moderate to severe injuries, especially hand or face
- Injuries that penetrate the periosteum or joint capsule
Should be assessed for rabies prophylaxis
Avoid primary wound closure except on the face, in which case it should be done with copious irrigation

Wound infections

Purulent wounds are often polymicrobial, and need to cover aerobes and anaerobes
Nonpurulent wounds are often monomicrobial with staphylococci and streptococci, but are also sometimes polymicrobial
Pasteurella is common in both
Antibiotic options
- Amox/clav is good empiric coverage
- 2nd and 3rd gen cephalosporins +/- clinda/metronidazole
- Carbapenems
- Moxifloxacin
- Doxycycline
- Septra + clinda/metronidazole
- Levfloxacin + clinda/metronidazole
Human bites also include streptococci, S. aureus, Eikonella corrodens, Fusobacterium, Peptostreptococcus, Prevotella, and Porphyromonas
- Eikonella is resistant to 1st-gen cephalosporins but amox/clav is good as is moxifloxacin

Tetanus toxoid

Give tetanus toxoid vaccine if not vaccinated within 10 years
Tdap preferred to Td, if they haven't previously received it

Cutaneous Anthrax

Background

Incubation period 1-12 days followed by pruritis, then papule, then vesicles, the finally painless ulcer with black eschar without pus
Eschar sloughs after 12-14 days
Surrounding edema can be minimal or severe and lymphadenopathy is common
Often mild systemic symptoms
Diagnosis
- Vesicles: unroof and soak 2 dry swabs in the vesicular fluid
- Ulcer: 2 moist swabs in the ulcer base or along the eschar edge
- Punch biopsy for immunohistochemistry or PCR

Management

Oral penicillin V 500 mg qid x7-10 days
If bioterrorism/aerosol exposure, ciprofloxacin 500 mg po bid or levofloxacin 500 mg poVI daily for 60 days

Bacillary Angiomatosis and Cat Scratch Disease

Background

Cat scratch disease

Caused by Bartonella henselae
After an incubation period of 3-30 days following a scratch or bite, a papule or pustule forms
Lymphadenopathy develops at about 3 weeks, and resolveds within 1-6 months
Occasionally, nodes can drain; rarely, extranodal visceral disease can occur

Bacillary angiomatosis

Caused by Bartonella henselae or B. quintana in immunocompromised patients, especially those with AIDS
Can appear either as red papular that vary in size (millimeter to centimeters) and number (1 to 1000), or as subcutaneous, painful nodules with overlying normal or dusky skin

Diagnosis

Fastidious, difficult-to-grow
Serology cross-reacts between B. henselae and B. quintana
PCR is one option

Management

Cat scratch disease

If >45 kg: azithromycin 500 mg on day 1 then 250 mg daily for 4 more days
If <45 kg: azithromycin 10 mg/kg on day 1 then 5 mg/kg daily for 4 more days

Bacillary angiomatosis

Erythromycin 500 mg qid or doxycycline 100 mg bid for 2 weeks to 2 months

Erysipeloid

Background

Cutaneous infection caused by Erysipelothrix rhusiopathiae, a thin, pleomorphic, non-spore-forming Gram-positive rod
Acquired by handling fish, marine animals, swine, or poulty
Incubation period of 1 to 7 days, followed by red maculopapular lesion on fingers or hands, spreading centrifugally with central clearing
May have a blue ring with peripheral red halo (target appearance)
Lymphadenopathy is common, though systemic symptoms are not
Diagnosed by aspirate and culture

Management

Penicillin 500 mg qid or amoxicillin 500 mg tid for 7 to 10 days
ALternatives include cephalosporins, clindamycin, and fluoroquinolones
Resistant to vancomycin, teicoplanin, and daptomycin

Glanders

Caused by Burkholderia mallei, an aerobic Gram-negative rod
Acquired from horses and mules through skin contact or inhalation
Causes ulcerating nodular lesions of the skin and mucosa
Treated with ceftazidime, gentamicin, imipenem, doxycycline, or ciprofloxacin for a prolonged course (?6 months)

Bubonic Plague

Caused by Yersinia pestis, a facultative anaerobic Gram-negative coccobacillus
Acquired from rodents
Three syndromes:
- Bubonic
  - Most common and classic, acquired from infected fleas or through breached skin
  - Incubation period of 2 to 6 days followed by fever, headache, chills, and regional lymphadenopathy
  - Skin lesion sometimes present at site of entry
  - May progress to septicemia and secondary pneumonia
- Septicemic
- Pneumonic
  - Transmissible human-to-human
Diagnosis made by blood culture, lymph node aspirate, or PCR; serology may be helpful for confirming the diagnosis retrospectively
Treatment
- Streptomycin 15 mg/kg bid for 10 to 14 days
- Alternatives: genatmicin, tetracycline, chloramphenicol, maybe fluoroquinolones
- If pneumonic form develops, needs to be in droplet isolation until 48 hours of effective therapy

Tularemia

Gram-negative coccobacillus Francisella tularensis
Distinct syndromes:
- Ulceroglandular
- Glandular
- Typhoidal
- Pneumonic
- Oculoglandular
- Oropharyngeal
Acquired by handling infected animals, by tick bites, sometimes by animal bites (especially cats), as well as by biting flies or mosquitoes
Skin ulcer forms at site of bite after 3-10 days with tender adenopathy, fevers, headache, and malaise (ulceroglandular syndrome)
If the ulcer heals quickly, with ongoing symptoms, they may present without the ulcer as glandular syndrome
Diagnosis
- Serology
- Culture with cysteine-supplemented media; notify the lab first
- PCR may be useful
Treatment
- Streptomycin 15 mg/kg/day q12h (max 2 g per day)
- Gentamicin 1.5 mg/kg q8h (or 2 mg/kg q8h in children)
- Duration 7-10 days, 14 days if severe
- Fluoroquinolones, tetracycline, or doxycycline can be used in mild to moderate cases, for a total of 14 days for oral therapy
- Inherent resistance to beta-lactams
High rate of relapse

Immunocompromised Patients

Infections may appear different or less pronounced due to the damped host immune response
Differential diagnoss should include
- Infectious: bacterial, fungal, viral, and parasitic infections
- Non-infectious: drug eruption, cutaneous infiltration of malignancy, chemotherapy reactions, radiation reactions, Sweet syndrome, erythema multiforme, leukocytoclastic vasculitis, and graft-vs-host disease
Biopsy or aspiration should be implemented early

Cancer Patients with Febrile Neutropenia

Early aspiration or biopsy for etiology
Risk stratify with MASCC score
Investigate with blood cultures, CXR +/- chest CT

Ecthyma gangrenosum

A cutaneous vasculitis caused by invasion of the vessel wall media and adventitia by bacteria
Presents as painless erythematous papules that progress to pain and necrosis within 24 hours
Usually lower extremity
Caused by Pseudomonas aeruginosa, but also other Gram-negatives, some Gram-positives, and fungi, even HSV

Management

Vancomycin plus antipseudomonal antibiotics
Duration for most SSTIs is 7 to 14 days
Surgical intervention for source control, if appropriate
G-CSF is not routinely recommended
Acyclovir if disseminated HSV or VZV is suspected

Persistent or recurrent

Consider yeasts and molds, so need to add empiric antifungals
- Candida spp. should be treated with an echinocandin
  - C. parapsilosis should be treated with amphotericin
  - Fluconazole is acceptable if sensitive
  - Duration is two weeks
- Aspergillus spp. should be treated with voriconazole or amphotericin, posaconazole, or echinocandin
  - Duration is 6 to 12 weeks
- Mucor/Rhizopus should be treated with amphotericin or posaconazole +/- an echinocandin
- Fusarium should be treated with high-dose voriconazole or posaconazole
Ensure resistant bacteria are covered as well, with MRSA coverage and other broad-spectrum
Add acyclovir if HSV or VZV is suspected; PCR from blood may be helpful
Blood cultures and skin biopsy, aspiration, or culture is recommended for diagnosis
Galactomannan is unhelpful in patients on antifungals

Cellular Immunodeficiency

Lymphoma, leukemia, HSCT or SOT recipients, steroid use, other immunosuppressive agents
Consult a dermatologist, consider biopsy
Empiric antibiotcs, antifungals, and/or antivirals in life-threatening situations

Nontuberculous Mycobacteria

Mostly occurs at site of innoculation but can have hematogenous dissemination
Most common in SOT is cutaneous and pleuropulmonary disease
Most common in HSCT is cather-related infections and bacteremias
Mycobacterium avium complex occurs in HIV disease
Non-HIV species include: M. fortuitum, M. chelonae, M. abscessus, M. ulcerans, M. kansasii, M. haemophilum, M. marinum, M. mucogenicum
Skin infections can include a poorly-resolving cellulitis, painless 1 to 2 cm nodules, necrotic ulcers, and subcutaneous abscesses
Treatment is with combination antibiotics for 6 to 12 weeks
- Macrolide plus second agent that it is susceptible
- See ATS/IDSA Guidelines 2007

Nocardia

Cutaneous Nocardia is usually metastatic from a primary pulmonary infection
Species include N. farcinica, N. brasiliensis, and others
Skin involvement is usually subcutaneous nodules, abscesses, and panniculitis, often cold and painless
Septra for 6 to 24 months, though combination therapy should be considered in severe infections
Debride necrotic nodules and large abscesses

Fungi

Most common causes of cutaneous infection include Aspergillus, Mucormycosis, Scedosporium, and Fusarium
Can present as papules, nodules, ulcers, and ecthyma gangrenosum
Skin biopsy is helpful in diagnosis
Voriconazole good for Aspergillus, Scedosporium, and Fusarium
Cryptococcal infections usually involve lungs, with hematogenous spreading
- Papules, nodules, pustules, chronic draining necrotic ulcers, or cellulitis
- Fluconazole for milder infections
Disseminated histoplasmosis is rare and is treated with amphotericin for 1 to 2 weeks followed by itraconazole for 6 to 12 months

Viruses

VZV is common, sometimes disseminated
- Dermatomal pain often preceeds the lesions by 24- to 72 hours
- Duration of disease usually 2 weeks, but may progress slower in immunodeficient patients
- Treated with high-dose IV acyclovir
- Suspect resistance if it develops while on prophylaxis
HSV also common
- Orofacial and genital sites most common, but can autoinnoculate any area
- Often preceded by local pain or tingling
- Disseminated disease is rare and usually associated with HSV-2
- Acyclovir, famciclovir, and valacyclovir are all options
- Foscarnet needed in cases of resistance

Parasites

Strongyloides stercoralis, amebae (Acanthamoeba and Balamuthia), Trypanosoma cruzi, and Sarcoptes scabiei (Norwegian scabies)