CellulitisEdit
Cellulitis is a common acute bacterial infection that involves the deeper layers of the skin and the subcutaneous tissues. It most often affects the lower limbs but can occur on any part of the body. The illness presents with warmth, redness, swelling, and pain in the affected area, and it can progress rapidly if not treated. The usual culprits are skin-dwelling bacteria such as Streptococcus pyogenes and Staphylococcus aureus, with the latter increasingly including methicillin-resistant strains in some communities. Breaks in the skin, chronic swelling (lymphedema), venous insufficiency, diabetes, immune suppression, and recent surgical wounds or trauma all raise the risk of infection. Early recognition and appropriate therapy reduce the chance of spread and systemic involvement, and practitioners carefully distinguish cellulitis from dermatitis, contact irritant rashes, and more serious infections such as necrotizing fasciitis necrotizing fasciitis.
In many settings, cellulitis is treated on an outpatient basis, reflecting a balance between effective care and minimizing unnecessary hospitalizations. The burden of disease on patients and health systems remains meaningful, given the need for antibiotics, follow-up, and management of underlying risk factors such as edema edema and skin breakdown. Ongoing discussion in medical practice emphasizes antibiotic selection, duration of therapy, and the role of diagnostic imaging in select cases, all in the context of antibiotic stewardship and cost-conscious care.
Epidemiology
Cellulitis occurs across ages and settings, though risk is higher with breaks in the skin, poor circulation, or immune compromise. Nonpurulent cellulitis, often caused by streptococci, tends to be managed with antibiotics that cover beta-hemolytic streptococci, while purulent variants with abscess formation more commonly involve Staphylococcus aureus including MRSA Staphylococcus aureus strains in certain regions. Accurate incidence data depend on the population studied and the diagnostic criteria used, but cellulitis remains a frequent reason for antibiotic prescriptions and urgent care visits.
Pathophysiology
The infection extends into the dermis and subcutaneous fat, usually after a breach of the skin barrier. Bacteria migrate into superficial tissues and trigger inflammation, edema, and pain. In nonpurulent cellulitis, the inflammatory response is typically driven by streptococci, whereas purulent cellulitis reflects abscess formation and a higher likelihood of MRSA involvement. Lymphatic spread can produce streaking and regional tenderness. Chronic edema, venous insufficiency, and lymphatic dysfunction create a milieu that predisposes to recurrent episodes and complicates healing.
Clinical presentation
Nonpurulent cellulitis
Patients often notice a red, warm, and tender plaque that expands gradually. The border may be ill-defined, and systemic symptoms such as fever and malaise occur less frequently in uncomplicated cases. Lower-extremity involvement is common, though any skin area can be affected.
Purulent cellulitis
Purulent drainage or an abscess frequently accompanies the infection. Patients may report localized pain and swelling with a palpable fluctuant area indicating pus collection. MRSA risk is higher in some communities, influencing antibiotic choice.
Red flags and differential considerations
Rapid progression, severe pain disproportionate to exam findings, bullae, skin color change suggesting necrosis, crepitus, or systemic toxicity should prompt urgent evaluation for complications such as necrotizing soft-tissue infection necrotizing fasciitis or sepsis. Other conditions that mimic cellulitis include dermatitis, venous stasis changes, intertrigo, and deep-seated infections; imaging and laboratory studies help clarify the diagnosis when the clinical picture is unclear.
Diagnosis
Clinical assessment
Diagnosis relies primarily on history and examination: localized warmth, swelling, redness, and tenderness consistent with cellulitis. The appearance, distribution, and presence of abscess or drainage guide management decisions.
Laboratory tests
In mild cases, laboratory testing may not be necessary. In suspected systemic involvement or severe illness, tests such as a complete blood count (CBC) and inflammatory markers (eg, C-reactive protein) can aid assessment. Blood cultures are reserved for patients with signs of systemic infection or high risk of bacteremia, since positivity is uncommon in uncomplicated cases.
Imaging
Imaging is not routinely required for straightforward cellulitis but can be helpful when there is concern for deeper infection, abscess, or alternative diagnoses. Bedside ultrasound can detect abscesses or fluid collections; computed tomography (CT) may be indicated if necrotizing infection is suspected or if deep tissue involvement is possible.
Microbiology
Microbiological testing is typically not needed for uncomplicated cases. Cultures may be obtained from purulent drainage or abscesses to guide targeted therapy, especially when initial treatment fails or in recurrent infections.
Management
Outpatient management
Uncomplicated, nonpurulent cellulitis without systemic toxicity is usually treated with oral antibiotics that cover common skin pathogens and have favorable tolerability. Examples include drugs targeting streptococci and common staphylococci. Antibiotic choice should be guided by local resistance patterns and patient allergy history; alternatives may be used if MRSA is a concern. Clear instructions on administration, anticipated duration, signs of improvement, and when to seek follow-up are essential. Elevation of the affected limb and wound care help reduce swelling and discomfort.
Inpatient management
Hospitalization is indicated for patients with systemic signs of illness (fever, tachycardia, hypotension), extensive or rapidly spreading infection, immunosuppression, significant comorbidities, or failure of outpatient therapy. Intravenous antibiotics are chosen to cover streptococci and staphylococci and may include agents such as a beta-lactam plus an anti-MRSA agent depending on the local pathogen profile and patient risk factors. Early assessment for potential abscesses requiring drainage is important, as drainage is a key part of management when present.
Antibiotic therapy
Empiric therapy should cover the most likely organisms in the given setting, with adjustments made for purulent disease, high MRSA prevalence, or penicillin allergy. For nonpurulent cellulitis, regimens typically include agents active against streptococci and non-MRA staphylococci. For purulent cellulitis, MRSA-active agents are often selected. In all cases, therapy should be reassessed within 48–72 hours based on clinical response and microbiology results if available. Narrowing therapy to targeted agents when pathogens are identified is a core principle of antibiotic stewardship.
Duration and follow-up
Most straightforward cases improve within 48–72 hours of appropriate therapy. A total course commonly ranges from 5 to 7 days for uncomplicated cases, with extension up to 10 days if there is slower improvement or complicating factors. Shorter courses are increasingly supported by guidelines when clinical response is favorable. Patients should be advised on limb elevation, wound care, glycemic control where applicable, and when to return for reassessment.
Abscess management
If an abscess is present, incision and drainage are typically required in addition to antibiotic therapy. Drainage reduces bacterial load and enhances antibiotic effectiveness. Ultrasound guidance may assist in locating fluid pockets.
Prevention
Preventive measures focus on reducing recurring episodes and optimizing skin and tissue health. Managing chronic edema, treating venous insufficiency, carefully inspecting skin for breaks, and promptly addressing skin trauma can lower risk. In people with diabetes or immune suppression, stricter control of underlying conditions and regular foot and skin care are important. Where relevant, vaccination against certain pathogens and adherence to hygiene practices supports overall skin health.