Cellulitis is an acute infection of skin and soft tissues characterized by localized pain, swelling, tenderness, erythema, and warmth.
The eMedicine Emergency Medicine article Cellulitis and the Medscape CME course Managing the Complicated Skin and Soft Tissue Infection may be of interest.
Cellulitis usually follows a break in the skin, such as a fissure, cut, laceration, insect bite, or puncture wound. Facial cellulitis of odontogenic origin may also occur. Patients with toe web intertrigo and/or tinea pedis and those with lymphatic obstruction, venous insufficiency, pressure ulcers, and obesity are particularly vulnerable to recurrent episodes of cellulitis.1, 2, 3 Organisms on the skin and its appendages gain entrance to the dermis and multiply to cause cellulitis. The vast majority of cases are caused by Streptococcus pyogenes or Staphylococcus aureus. Occasionally, cellulitis may be caused by the emergence of subjacent osteomyelitis. Cellulitis may rarely result from the metastatic seeding of an organism from a distant focus of infection, especially in immunocompromised individuals. This is particularly common in cellulitis due to Streptococcus pneumoniae and marine vibrios.
Because cellulitis is not a reportable disease, the exact prevalence is uncertain; however, it is a relatively common infection. A 2006 study found an incidence rate of 24.6 cases per 1000 person-years.4
Cellulitis has been found to account for approximately 3% of emergency medical consultations at one United Kingdom district general hospital.
Cellulitis generally is a localized infection. Most patients treated appropriately recover completely. Mortality is rare (5%) but may occur in neglected cases or when cellulitis is due to highly virulent organisms (eg, Pseudomonas aeruginosa). Factors associated with an increased risk of death are the presence of concurrent illness (eg, congestive heart failure, morbid obesity, hypoalbuminemia, renal insufficiency) or complications (eg, shock).5
No racial predilection has been noted.
No predilection for either sex is usually reported, although a higher incidence among males has been reported in one study.4
No age predilection is usually described; however, recent studies found a higher incidence of cellulitis in general among individuals older than 45 years.2, 4 Moreover, cellulitis at certain anatomic sites may show a predilection for persons in certain age groups.
Facial cellulitis is more common in children younger than 3 years.
Perianal cellulitis is predominantly a disease of children.6
The incubation period is somewhat organism dependent. Postoperative cellulitis at the surgical site due to group A beta-hemolytic streptococci may develop rather rapidly. On the other hand, cellulitis due to staphylococci usually is delayed in onset.
Patients report local pain and swelling at the site of cellulitis.
The patient may report a history of trauma to the site. Severe bacterial cellulitis may occur as a postsurgical complication, such as following hip replacement7 or liposuction, or secondary to lymphatic occlusion following either radical mastectomy8, 9 or conservative breast surgery10; impaired lymphatic drainage and edema are also considered predisposing factors to leg cellulitis following saphenous vein resection for coronary artery bypass.11 However, cellulitis may follow a trivial injury to the skin (eg, scratch, abrasion, animal bite, intravenous or subcutaneous drug injection, body piercing).12, 13, 14
Fever is common, and chills may be noted, particularly if suppuration has occurred.
Malaise may be present.
The clinical appearance of cellulitis is shown in Media Files 1-3.
Involved sites are red, hot, swollen, and tender.
Unlike erysipelas, the borders are not elevated or sharply demarcated.
Lymphangitis, regional lymphadenopathy, or both may be present.
Fever is common.
In severe cases, patients may develop hypotension.
Local suppuration may follow if therapy is delayed.
Overlying skin may develop areas of necrosis.
The most commonly involved site is the leg.4, 15
Perianal cellulitis due to group A streptococci is usually observed among children with perianal fissures. It is characterized by perianal erythema and pruritus, painful defecation, and bleeding in the stools.6
Pneumococcal facial cellulitis occurs primarily in young children who are at risk for pneumococcal bacteremia.16, 17 It may manifest as two distinctive clinical syndromes.
Extremity involvement in individuals with diabetes mellitus or substance abuse
Head, neck, and upper torso involvement in individuals with systemic lupus erythematosus, nephrotic syndrome, or hematologic disorders
In immunocompetent individuals, cellulitis is usually due to S pyogenes and, occasionally, S aureus.5, 18, 19 Isolation of methicillin-resistant S aureus (MRSA) is steadily increasing.20 Bacterial strains may also show multiple resistance to other standard antibiotic treatments, including erythromycin.
Recurrent staphylococcal cellulitis may occur in patients with nasal carriage of staphylococci and those with Job syndrome. S aureus is also the leading cause of soft tissue infections in persons who abuse injection drugs.21
Recurrent cellulitis due to streptococci may be observed in patients with chronic lymphedema (eg, from lymph node dissection, irradiation, Milroy disease, elephantiasis).18, 22 Streptococcal infections are also common in injection drug users.23
Non–group A streptococci (ie, groups B, C, and G) are commonly implicated in cellulitis in patients with lymphatic obstruction or venectomy for coronary artery bypass graft.11, 24
S pneumoniae is an uncommon cause of cellulitis in adults.17, 25, 26 Pneumococcal cellulitis may occur via bacteremia. In a review of pneumococcal skin infection in adults, all such patients had an underlying chronic illness or were immunocompromised by drug or alcohol abuse.27 Pneumococcal facial cellulitis occurs primarily in young children at risk for pneumococcal bacteremia.16, 28
Patients who are immunocompromised with granulocytopenia, such as renal transplant recipients, may develop cellulitis due to infection with other organisms, including gram-negative bacilli (eg, Pseudomonas, Proteus, Serratia, Enterobacter, Citrobacter), anaerobes, other opportunistic pathogens (eg, Helicobacter cinaedi, Fusarium species), mycobacteria, and fungi (eg, Cryptococcus).29, 30, 31, 32, 19, 33, 34, 35 Preseptal cellulitis caused by dermatophytes is rarely observed, mostly in the pediatric age group.36 Persistent cellulitis due to Cryptococcus neoformans infection has also been reported in a patient receiving renal dialysis.37
Escherichia coli may be responsible for cellulitis in patients with nephrotic syndrome.38
Cellulitis from unusual bacterial species, including Enterococcus faecalis, Enterobacteriaceae, and Bacteroides and Clostridium species, may be observed following subcutaneous injections of illegal drugs.39 If Clostridium species or other anaerobes cause the infection, crepitant cellulitis is often observed clinically.
Other uncommon causes of cellulitis include Neisseria meningitidis; Pasteurella multocida, following animal bites; Aeromonas hydrophilia, following contact with fresh water; Streptococcus iniae, a fish pathogen causing infections in aquaculture farms; and Vibrio vulnificus, following contact with seawater. Cellulitis from marine vibrios in hepatopathic patients may also follow ingestion of contaminated raw oysters.40, 41, 42, 43, 44, 45 Haemophilus influenzae has become a rare cause of buccal cellulitis in children after the introduction of the H influenzae type B vaccine.46, 47