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Cellulitis is "an acute, diffuse, and suppurative inflammation of loose connective tissue, particularly the deep subcutaneous tissues, and sometimes muscle, which is most commonly seen as a result of infection of a wound, ulcer, or other skin lesions." [1] The condition has been known from antiquity; generations of medical students learned its signs as rubor, tumor, calor, dolor or "reddened, swollen, warm to the touch, and painful." The presence of broken skin in the inflamed area is a further warning, but there may be no obvious wound.

The most common organisms are:[2]

If purulence is present, then stept is the cause of < 10% of cases.[3]

One study found that about 75% of cases are due to Streptococcus pyogenes and that beta-lactam antibiotics ineffective against MRSA are effective for cellulitis.[4]

Differential diagnosis to rule out life-threatening conditions, such as deep venous thrombosis, compartment syndrome and gangrene, is essential; a presentation of the common signs of cellulitis needs urgent, if not emergent, evaluation.


According to the 2014 clinical practice guidelines, antribiotics or outpatients should be "an antimicrobial agent that is active against streptococci...For patients whose cellulitis is associated with penetrating trauma, evidence of MRSA infection elsewhere, nasal colonization with MRSA, injection drug use, or SIRS (severe nonpurulent; Figure 1), vancomycin or another antimicrobial effective against both MRSA and streptococci is recommended (strong, moderate)".[5]

According to the 2011 clinical practice guidelines, if both Methicillin resistant Staphylococcus aureus and Streptococcus pyogenes are possible causes, then "options include the following: clindamycin alone (A-II) or TMP-SMX or a tetracycline in combination with a β-lactam (eg, amoxicillin) (A-II) or linezolid alone (A-II)."[6]

According to the 2005 clinical practice guidelines, which state that staphylococcus aureus is very uncommon: "Suitable agents include dicloxacillin, cephalexin, clindamycin, or erythromycin, unless streptococci or staphylococci resistant to these agents are common in the community."[7] A more recent trial confirms that if purulence or diabetes are not present then coverage for staphylococcus aureus is not needed.[8]

A study of failed treatment, although 48% of these patients had a cutaneous abscess, concluded that failure is reduced if:[9]

If levofloxacin is used for treatment, 5 days is as effective as 10 days.[10] However, levoflaxacin is ineffective against methicillin-resistant Staphylococcus aureus.


Penicillin 250 mg twice a day by mouth can prevent cellulitis in the leg according to a randomized controlled trial.[11]


  1. Anonymous (2021), Cellulitis (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. Chira, S; L G Miller (2009-08-03). "Staphylococcus aureus is the most common identified cause of cellulitis: a systematic review". Epidemiology and Infection: 1-5. DOI:10.1017/S0950268809990483. ISSN 0950-2688. PMID 19646308. Retrieved on 2009-09-01. Research Blogging.
  3. Moran GJ, Krishnadasan A, Gorwitz RJ, Fosheim GE, McDougal LK, Carey RB et al. (2006). "Methicillin-resistant S. aureus infections among patients in the emergency department.". N Engl J Med 355 (7): 666-74. DOI:10.1056/NEJMoa055356. PMID 16914702. Research Blogging.
  4. Jeng A, Beheshti M, Li J, Nathan R (2010). "The role of beta-hemolytic streptococci in causing diffuse, nonculturable cellulitis: a prospective investigation.". Medicine (Baltimore) 89 (4): 217-26. DOI:10.1097/MD.0b013e3181e8d635. PMID 20616661. Research Blogging.
  5. Stevens DL, Bisno AL, Chambers HF, Dellinger EP, Goldstein EJ, Gorbach SL et al. (2014). "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 59 (2): e10-52. DOI:10.1093/cid/ciu444. PMID 24973422. Research Blogging.
  6. Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ et al. (2011). "Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children: executive summary.". Clin Infect Dis 52 (3): 285-92. DOI:10.1093/cid/cir034. PMID 21217178. Research Blogging.
  7. Stevens DL, Bisno AL, Chambers HF, et al. (November 2005). "Practice guidelines for the diagnosis and management of skin and soft-tissue infections". Clin. Infect. Dis. 41 (10): 1373–406. DOI:10.1086/497143. PMID 16231249. Research Blogging.
  8. Pallin DJ, Binder WD, Allen MB, Lederman M, Parmar S, Filbin MR et al. (2013). "Clinical Trial: Comparative effectiveness of cephalexin plus trimethoprim-sulfamethoxazole vs. cephalexin alone for treatment of uncomplicated cellulitis: A randomized controlled trial.". Clin Infect Dis. DOI:10.1093/cid/cit122. PMID 23457080. Research Blogging.
  9. Halilovic J, Heintz BH, Brown J (2012). "Risk factors for clinical failure in patients hospitalized with cellulitis and cutaneous abscess.". J Infect. DOI:10.1016/j.jinf.2012.03.013. PMID 22445732. Research Blogging.
  10. Hepburn, Matthew J; David P Dooley, Peter J Skidmore, Michael W Ellis, William F Starnes, William C Hasewinkle (2004-08-09). "Comparison of short-course (5 days) and standard (10 days) treatment for uncomplicated cellulitis". Archives of Internal Medicine 164 (15): 1669-1674. DOI:10.1001/archinte.164.15.1669. ISSN 0003-9926. PMID 15302637. Retrieved on 2009-09-01. Research Blogging.
  11. Thomas, Kim S.; Angela M. Crook, Andrew J. Nunn, Katharine A. Foster, James M. Mason, Joanne R. Chalmers, Ibrahim S. Nasr, Richard J. Brindle, John English, Sarah K. Meredith, Nicholas J. Reynolds, David de Berker, Peter S. Mortimer, Hywel C. Williams (2013). "Penicillin to Prevent Recurrent Leg Cellulitis". New England Journal of Medicine 368 (18): 1695-1703. DOI:10.1056/NEJMoa1206300. ISSN 0028-4793. Retrieved on 2013-05-02. Research Blogging.