Talan DA, Mower WR, Krishnadasan A, et al. Trimethoprim-Sulfamethoxazole versus Placebo for Uncomplicated Skin Abscess. N Engl J Med. 2016 Mar 3;374(9):823-32. doi: 10.1056/NEJMoa1507476. PMID: 26962903; PMCID: PMC4851110.
Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the infectious diseases society of America. Clin Infect Dis. 2014 Jul 15;59(2):147-59. doi: 10.1093/cid/ciu296. Epub 2014 Jun 18. PMID: 24947530.
Furuncles, carbuncles, and abscesses are the more common types of purulent skin and soft tissue infections (SSTIs).
Etiology and PathogenesisTop
Furuncles and carbuncles are typically caused by Staphylococcus aureus (both methicillin-susceptible Staphylococcus aureus [MSSA] and methicillin-resistant Staphylococcus aureus [MRSA]). Infections secondary to a penetrating trauma or involving the perioral or perineal area increase the likelihood of a polymicrobial infection, including S aureus, Streptococcus pyogenes, gram-negative bacilli, and anaerobes. Depending on host factors and exposures, other causes can include blastomycosis, cryptococcosis, nontuberculous mycobacterial infection, and nocardiosis.
Purulent SSTIs often affect healthy, immunocompetent adults. Risk factors are similar to those for nonpurulent SSTIs (see Table 10.3-2). Additional risk factors include immunocompromised state (particularly neutrophil defects), suboptimal hygiene (eg, sharing contaminated hygiene items like shaving razors), hot and humid climates, MRSA carriage, and additional MRSA risk factors (see Nonpurulent Skin and Soft Tissue Infections: Erysipelas and Cellulitis).
Clinical Features Top
SSTIs should be categorized as mild, moderate, or severe (see Table 10.3-3).
A furuncle is a well-demarcated, painful nodule involving a hair follicle that frequently occurs in areas of friction (neck, axillae, thighs, buttocks). Its extension into dermal and subcutaneous tissue can result in suppurative abscesses and cellulitis. Carbuncles can occur anywhere but often develop at the back of the neck. If a carbuncle forms, patients can have associated systemic symptoms (eg, fevers, chills, rigors). Both furuncles and carbuncles (especially the latter) can be further complicated by bacteremia, toxic shock syndrome, necrotizing fasciitis, and sites of metastatic infection (eg, osteomyelitis, endocarditis).
Other considerations include the location of the abscess, whether it is amenable to drainage, and if there are any predisposing conditions. For example, the presence of perianal abscesses in a patient with chronic diarrhea should prompt consideration of Crohn disease, whereas recurrent abscesses since young childhood should prompt consideration of underlying immunodeficiency, such as chronic granulomatous disease.
The diagnosis is generally clinical. Laboratory investigations are not required in a mild, uncomplicated infection in an immunocompetent host. If there is evidence of purulent drainage, wound samples can be obtained and sent for Gram staining and culture. However, this does not preclude the initiation of treatment, if indicated.
Cultures of blood, wounds, and drainage fluid at the time of incision and drainage (I&D) are indicated prior to initiation of antimicrobial therapy in the following circumstances:
1) The patient being systemically unwell.
2) Failure of prior antibiotic therapy.
3) History of recurrent or multiple abscesses.
4) Immersion injury or animal bite.
5) Immunocompromise and other comorbidities (eg, malignancy, neutropenia, splenectomy, immunodeficiency).
Ultrasonography should be performed if there is clinical suspicion of an abscess. Radiography can be considered to assess for subcutaneous gas but it will not exclude a deeper SSTI.
1) Nodular lymphangitis (eg, sporotrichosis, nocardiosis, Mycobacterium marinum infection, cutaneous leishmaniasis, dimorphic fungal infections).
1) Erythema nodosum and pyoderma gangrenosum.
2) Epidermoid cyst.
3) Hidradenitis suppurativa.
Many of these noninfectious causes can become secondarily infected.
All purulent SSTIs should have definitive source control. Furuncles will often rupture and spontaneously begin draining with application of warm compresses. Larger furuncles and carbuncles often require I&D, and >80% of furuncles resolve with I&D. Antibiotics should be used if there is evidence of cellulitis beyond the furuncle itself (Table 10.3-1). Ultrasound-guided aspiration alone is insufficient and often results in treatment failure.
Depending on the location of the abscess, the risk of a polymicrobial infection may be increased (eg, perirectal abscesses) and this will alter antimicrobial therapy choices.
Recurrent skin abscesses at the same site should prompt evaluation of other local causes, such as hidradenitis suppurativa, foreign body/material, or pilonidal cysts. Recurrent abscesses should be drained and samples should be sent for culture. Underlying immunodeficiencies, such as chronic granulomatous disease, should be investigated in adults with recurrent abscesses that began in early childhood.
– I&D and antibiotic therapy
– Empiric treatment options:
1) Cephalexin if there is low risk for MRSA or confirmed MSSA
– If polymicrobial coverage is required (eg, perioral/perirectal abscess, penetrating trauma): amoxicillin/clavulanate ± doxycycline/SMX-TMP
– I&D and antibiotic therapy
– Empiric treatment options: one of vancomycin, daptomycinc, or linezolidc
One of the following combinations:
2) Ciprofloxacin and metronidazoled
3) Ceftriaxone and metronidazolee
– Adjust treatment options based on susceptibilities
a Oral antibiotics with activity against Staphylococcus aureus can be considered in case of extensive surrounding cellulitis, immunocompromised state, inadequate response to I&D alone (with good source control), abscess size >2 cm.
b Clindamycin may be considered if clindamycin local resistance is <10%-15% and/or there are other compelling indications. It should be avoided as a first-line option.
c Consultation with infectious diseases is recommended prior to initiation of these agents.
d Review local antibiogram data if this combination is being used for coverage of Pseudomonas aeruginosa.
e If the patient has risk factors for P aeruginosa infection, this combination would not provide adequate coverage.
I&D, incision and drainage; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus; SMX-TMP, sulfamethoxazole/trimethoprim.