General
Cellulitis is a common bacterial infection of the deep dermis and subcutaneous tissue characterized by erythema, pain, warmth, and swelling. Pathogens causing cellulitis are strongly correlated with age and immune status:
Immunocompetent adults: common etiologies include Staphylococcus aureus (particularly if there is concurrent purulence) and Streptococcus pyogenes.
Immunocompromised individuals: common pathogens such as S aureus and Streptococcus should be considered, but gram-negative pathogens should also be considered and covered.
A focused history should determine immune status, comorbid conditions, possible sites and causes of skin barrier disruption, prior history of cellulitis, and methicillin-resistant S aureus (MRSA) risk factors, as well as community prevalence of MRSA. The most common route of bacterial seeding in immunocompetent individuals is via direct inoculation, and in immunocompromised individuals, it is via hematogenous seeding.
Risk factors for developing cellulitis include minor skin trauma, atopic dermatitis, contact dermatitis, body piercings, intravenous (IV) drug use, tinea pedis infection, animal bites, peripheral vascular disease, obesity, older age, immune suppression (chronic systemic steroid use, neutropenia, immunosuppressive medications, organ transplantation, HIV), and lymphatic damage (lymph node dissection, radiation therapy, vein harvest for coronary artery bypass surgery / saphenous venectomy, and damage that occurs following multiple prior episodes of cellulitis).
Fevers, chills, and malaise may precede the onset of cellulitis but may also be absent. Poorly defined borders, erythema, swelling, tenderness, and warmth characterize typical cellulitis lesions. In adults, the extremities, particularly the lower extremities, are the most common sites affected. In more severe cases, additional clinical features may include vesicle and bullae formation, pustules, and necrosis. Complications are not common but can include glomerulonephritis, lymphadenitis, and bacteremia.
A rising prevalence of MRSA has been identified as a pathogen of skin and soft tissue infections in otherwise healthy individuals lacking the aforementioned risk factors for cellulitis. MRSA should be considered for penetrating traumas, purulent infections, and in specific populations: athletes, children, prisoners, military service members, long-term care residents, and IV drug users. Other MRSA risk factors include recent admission to a health care facility, presence of an indwelling catheter, poor personal hygiene, and history of MRSA.
Recurrent Cellulitis: Major risk factors for recurrent cellulitis include chronic edema, dermatomycosis, and lymphatic or venous insufficiency. Prior episodes of cellulitis, immunodeficient states, obesity, previous local surgery / saphenectomy, as well as having cancer, can also increase the risk of recurrent cellulitis.
Note: It is exceedingly rare for cellulitis to occur bilaterally simultaneously, so if redness and involvement of the legs are bilateral in a patient suspected to have cellulitis, consider an alternative diagnosis such as stasis dermatitis or contact dermatitis (allergic, irritant).
Cellulitis can be caused by many different bacterial pathogens, but the diagnosis is almost always made clinically. If a patient has had more than 1 episode of cellulitis, investigate risk factors for recurrent cellulitis but also consider alternative diagnoses.
Stasis dermatitis is a frequent cause of bilateral leg redness. There are usually no systemic signs or leukocytosis; it is commonly bilateral with pruritus and red-brown dyspigmentation.
The differential for cellulitis is vast, and time course, drug / exposure history, and the presence / absence of systemic features should help delineate the cause. Below are common differential diagnoses:
Cellulitis is an infection of the skin that is most often caused by the bacteria Staphylococcus ("staph") and Streptococcus ("strep"). These bacteria are able to enter the skin through small cracks (fissures), causing sudden redness, swelling, and warmth in an area of the skin. Cellulitis is sometimes accompanied by fever, chills, and feeling fatigued.
If the infection is left untreated for too long, cellulitis can result in abscesses (swollen, warm, tender lumps filled with pus) or the spread of bacteria into the bloodstream (bacteremia). However, most cases of cellulitis resolve with appropriate antibiotic therapy.
Who’s At Risk
Cellulitis can occur in anyone or any age, race / ethnicity, and sex. Factors that increase the risk of developing cellulitis include:
Diabetes.
Lymphedema.
Skin wounds.
Chronic lower leg swelling (edema).
Athlete's foot (tinea pedis).
Bites from insects, animals, or other humans.
Obesity.
Poor circulation in the legs (peripheral vascular disease).
Weakened immune system due to underlying illness or medication.
Intravenous drug abuse.
Signs & Symptoms
Cellulitis can affect any part of the body, but the most common locations are the:
Lower legs.
Arms or hands.
Face.
Cellulitis often appears initially as minimally inflamed skin. The involved area may rapidly become swollen, warm, and tender to the touch and increase in size as the infection spreads. In lighter skin colors, the area may be any shade of pink or red. In darker skin colors, the redness may be harder to see, or it may appear more purple or dark brown. Occasionally, red streaks may radiate outward from the cellulitis. Vesicles (small blisters) or bullae (pus-filled lesions larger than a thumbnail) may also be present.
Cellulitis may be accompanied by swollen lymph nodes, fever, chills, and fatigue.
Self-Care Guidelines
If you think you have cellulitis, make an appointment to see your medical professional. While you are waiting for the appointment, elevating the involved body part, if you are able, can help decrease swelling. A cool, clean, moist towel can be applied to the area to decrease pain.
When to Seek Medical Care
If you develop a painful, warm, enlarging area on your skin that is red or a darker color than your surrounding skin, make an appointment with your medical professional as soon as possible to get treatment and to avoid complications that may occur if cellulitis is left untreated. If you also have fever and chills or if the area involves the face, you should go to urgent care or the emergency room.
If you are currently being treated for a skin infection that has not improved after 2-3 days of antibiotics, return to your medical professional. You may need treatment with different medications, or the infection may have spread deeper into your skin.
Treatments
Your medical professional will usually be able to easily diagnose cellulitis by examining the affected area. Sometimes they may want to get additional information by ordering blood tests and/or performing a bacterial culture to identify the specific bacterium that is causing the cellulitis as well as to test its susceptibility to different antibiotics, which helps guide treatment decisions.
While waiting for the results from the bacterial culture, your medical professional may want to start you on an antibiotic to fight the most common bacteria that cause cellulitis. Once the final culture results have returned, your medical professional may change the antibiotic you are taking, especially if your infection is not improving.
Mild cases of cellulitis in a healthy person can be treated with oral antibiotics. Common antibiotics that are used to treat cellulitis include:
Trimethoprim-sulfamethoxazole (eg, Bactrim).
Doxycycline (eg, Vibramycin).
Minocycline (eg, CoreMino).
Clindamycin (eg, Cleocin).
Dicloxacillin.
Cephalexin (eg, Keflex).
Linezolid (eg, Zyvox).
If you are very sick or have other chronic illnesses that may complicate your recovery, you may need to be hospitalized to receive intravenous antibiotics. Common intravenous antibiotics that are used to treat cellulitis include:
Patient Information for Cellulitis in Adult