Cellulitis

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." 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:

• Staphylococcus aureus
• Streptococcus pyogenes (group A strept)

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

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.

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.

Treatment

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)".

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)."

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." A more recent trial confirms that if purulence or diabetes are not present then coverage for staphylococcus aureus is not needed.

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

• Higher dose antibiotics are used:
  • vancomycin at least 30 mg/kg/day
  • clindamycin at least 10 mg/kg/day (450 mg every 8 hours)
  • Trimethoprim-Sulfamethoxazole combination at least 5 mg/kg/day of trimethoprim (a single strength pill has 80 mg trimethoprim) (two double strength pills every 12 hours)

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

Prevention

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