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

• Staphylococcus aureus
• Streptococcus pyogenes

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

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

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)