Cellulitis: Recognition, Assessment, Resuscitation and Emergency Management

Learning objectives

• Define cellulitis and explain how bacteria enter and spread through skin and subcutaneous tissues.
• Identify risk factors, common organisms, typical findings and early systemic deterioration.
• Perform a structured primary survey and focused skin, limb and neurovascular examination.
• Distinguish cellulitis from erysipelas, abscess, necrotising fasciitis, DVT, allergic inflammation, burns and other mimics.
• Provide safe first aid, analgesia, wound care, sepsis treatment, antibiotic therapy and escalation.
• Plan nursing monitoring, documentation, discharge education, follow-up and recurrence prevention.

Definition and clinical concept

Cellulitis is an acute, spreading infection involving the deeper dermis and subcutaneous tissue. The infected skin becomes inflamed because bacterial products and the host immune response cause vasodilation, capillary leakage, oedema and leukocyte migration. Erysipelas is a more superficial infection with a raised, sharply demarcated border; in practice the two can overlap. A cellulitis lesion is usually unilateral, warm, tender, swollen and progressively red, although erythema can be difficult to appreciate on dark skin. The diagnosis is primarily clinical; a negative culture does not exclude it.

Cellulitis is not the same as an abscess. An abscess is a localised collection of pus that usually requires incision and drainage, whereas non-purulent cellulitis is treated primarily with antibiotics and treatment of the entry site. A patient may have both conditions.

Causative organisms and pathophysiology

• Beta-haemolytic streptococci (especially group A streptococcus) commonly cause non-purulent cellulitis and spread through lymphatics.
• Staphylococcus aureus, including community-associated MRSA where prevalent, is more likely with purulence, penetrating trauma, abscesses or injection drug use.
• Gram-negative and anaerobic organisms become more relevant in diabetic foot infection, chronic ulcers, perineal infection, immunosuppression, severe vascular disease, animal or human bites and water exposure.
• Special exposures: Pasteurella after dog or cat bites, Capnocytophaga in a person with asplenia or severe alcohol use, Vibrio after seawater or raw seafood exposure, and Aeromonas after fresh-water exposure.

Bacteria usually enter through a breach in the protective barrier: cracked toe-web skin, tinea pedis, eczema, ulcers, injection sites, trauma, surgical wounds, burns, pressure injury or an unnoticed fissure. Lymphatic obstruction, oedema and poor perfusion reduce local clearance and increase recurrence.

Risk factors and vulnerable patients

• Previous cellulitis or chronic lymphoedema.
• Tinea pedis, nail disease, eczema, scabies excoriations or chronic dermatitis.
• Diabetes mellitus, peripheral neuropathy, peripheral arterial disease or venous insufficiency.
• Obesity, immobility, chronic leg oedema, heart failure or nephrotic syndrome.
• Open wounds, ulcers, burns, pressure injuries, recent surgery or invasive devices.
• Immunosuppression, HIV, chemotherapy, long-term corticosteroids or splenectomy.
• Injection drug use, poor access to clean water, overcrowded living conditions or poor wound-care access.
• Animal or human bites, penetrating injuries, aquatic exposure and recent travel.
• Very young infants, older adults and pregnant patients may deteriorate with fewer local signs.

Typical presentation

Patients often report a progressively enlarging area of pain, warmth, swelling and redness over hours to several days. The border is usually poorly defined. Fever, chills, malaise, headache, myalgia, nausea and tender regional lymph nodes may occur. Lymphangitis appears as a red linear streak tracking proximally; lymphadenopathy may accompany it.

• Inspect colour and compare with the opposite side; palpate for warmth, tenderness, oedema and induration.
• Look for a portal of entry between toes, around nails, in a skin fold, at a wound or under a dressing.
• Mark the edge with date and time or photograph according to policy; this helps judge progression.
• Check for fluctuance, crepitus, bullae, dusky skin, skin anaesthesia, necrosis or pain beyond visible inflammation.
• Examine the whole limb, not only the reddest area, and assess joints above and below.

Red flags for severe infection or a deeper emergency

These signs may indicate sepsis, an abscess, necrotising fasciitis, orbital cellulitis, septic arthritis, osteomyelitis, flexor tenosynovitis or another condition requiring urgent senior and surgical review. Do not wait for imaging when a time-critical surgical diagnosis is clinically suspected.

First contact and scene safety

1. Perform hand hygiene and wear gloves; add eye and body protection if drainage or splashing is possible.
2. Introduce yourself, confirm identity, obtain consent and provide privacy, especially when examining groin, breast, buttock or genital lesions.
3. Ask about onset, speed of spread, fever, rigors, pain severity, trauma, bites, water exposure, wounds, injections and previous antibiotics.
4. Ask about diabetes, HIV, steroid use, chemotherapy, vascular disease, lymphoedema, drug allergies, pregnancy and kidney or liver disease.
5. Do not squeeze, lance or massage a suspected abscess in the field. Cover an open wound with a clean dressing and avoid contamination.
6. Check vital signs early. Any abnormal physiology changes cellulitis from a simple skin problem into a possible sepsis pathway.

Primary survey: ABCDE approach

A — Airway

• Assess speech, voice change, drooling, tongue or facial swelling and ability to handle secretions.
• Facial, neck, dental or submandibular infection can threaten the airway; call senior airway help early.
• Prepare suction, oxygen, airway equipment and a definitive-airway plan if swelling is progressing.

B — Breathing

• Count respiratory rate, assess work of breathing, oxygen saturation, chest movement and mental state.
• Give oxygen for hypoxaemia or shock according to local protocol; do not delay sepsis treatment while waiting for perfect observations.

C — Circulation

• Check pulse, blood pressure, capillary refill, skin temperature, peripheral pulses and urine output.
• Obtain IV access if the patient is systemically unwell; take blood samples and cultures before antibiotics only if this does not delay treatment.
• For suspected sepsis or hypoperfusion, follow the facility sepsis bundle: cautious isotonic crystalloid, repeated perfusion assessment and early vasopressor/senior support when fluid-responsive shock is absent.

D — Disability

• Assess AVPU or GCS, bedside glucose, pain score and new confusion.
• Hypoglycaemia, severe sepsis, hypoxia and medication effects can coexist; treat immediately reversible threats.

E — Exposure and examination

• Expose enough to inspect the entire skin surface while preventing heat loss and maintaining dignity.
• Measure and mark the affected area, inspect wounds and folds, palpate for fluctuance and crepitus, and check neurovascular status.
• Look at the feet, toe webs, nails, pressure points, sacrum and perineum; hidden portals are common.

Focused history

Focused examination and severity assessment

• Local: temperature, colour, borders, tenderness, induration, oedema, fluctuance, drainage, bullae, necrosis and crepitus.
• Regional: lymphangitis, lymph nodes, joint range of motion, tendon function and compartment firmness.
• Neurovascular: pulses, capillary refill, sensation, motor function and pain on passive stretch.
• Systemic: temperature, heart rate, blood pressure, respiratory rate, SpO2, mental state and urine output.
• Host: hydration, nutrition, glycaemic control, perfusion, immune status and ability to take oral medication.

Important differential diagnoses

Investigations

Most mild, typical cellulitis does not require extensive testing. Investigate according to severity, host factors, site and diagnostic uncertainty.

• Bedside glucose: essential in diabetes, altered mental state or severe infection.
• Full blood count, CRP/ESR and renal/electrolyte profile: useful when systemic illness, admission or IV therapy is likely.
• Lactate and blood gas: consider in shock, hypoperfusion or suspected sepsis; interpret with the whole clinical picture.
• Blood cultures: obtain in severe systemic illness, immunocompromise, unusual exposure or suspected bacteraemia; yield is low in uncomplicated cases.
• Wound or pus culture: collect from purulent material after cleaning; superficial swabs of intact cellulitic skin are often misleading.
• Ultrasound: useful for an occult abscess, retained foreign body or venous thrombosis when clinically indicated.
• Plain radiograph: consider foreign body, gas, bone involvement or severe diabetic foot infection.
• CT or MRI: for deep-space infection, osteomyelitis or uncertain anatomy after senior review; never let imaging delay surgery in suspected necrotising fasciitis.

Immediate treatment and first aid

1. Place the patient in a safe position, keep them warm and provide reassurance.
2. Remove constrictive jewellery or clothing from a swollen limb, documenting what was removed.
3. Clean visible contamination gently with clean water or saline; cover open areas with a sterile non-adherent dressing.
4. Elevate an affected limb where tolerated to reduce oedema, while checking that elevation does not worsen pain or perfusion.
5. Give analgesia according to protocol, reassess pain and avoid masking deterioration.
6. Check tetanus status for wounds and arrange vaccination or immunoglobulin when indicated by local guidance.
7. Do not apply irritant chemicals, herbal preparations, tight bandages or unprescribed steroids.
8. Escalate immediately if red flags, systemic illness, facial/eye involvement, rapidly spreading infection or high-risk host factors are present.

Antimicrobial management

Antibiotics should cover the likely organisms and be started promptly when cellulitis is clinically diagnosed. Choice, dose and duration depend on local resistance patterns, infection severity, allergy, renal function, pregnancy, age, site and culture results. Document the indication, route, first dose time, allergy check and planned review.

• Mild non-purulent cellulitis: an appropriate oral agent active against streptococci and susceptible staphylococci is commonly used according to Uganda/local protocol.
• Moderate infection, failed oral therapy or inability to absorb: consider hospital assessment and parenteral therapy with step-down to oral treatment after clear clinical improvement.
• Severe infection or sepsis: obtain cultures where feasible and start broad IV empiric therapy that covers streptococci, staphylococci and, when indicated, Gram-negative and anaerobic organisms. Review daily and narrow once results and clinical response are known.
• Purulence or abscess: source control through incision and drainage is central; add antibiotic therapy when systemic illness, extensive disease, rapid progression, immunocompromise or difficult sites are present.
• MRSA risk: consider prior MRSA, recent hospitalisation or antibiotics, penetrating trauma, injection drug use, recurrent abscess or local epidemiology.
• Bites and water exposure: use exposure-specific coverage and seek microbiology or infectious-disease advice.

Surgical and procedural management

• Drain every clinically significant abscess and send pus for culture when appropriate.
• Remove foreign bodies, devitalised tissue, infected sutures or obstructing material after appropriate assessment.
• Request urgent surgical review for suspected necrotising infection, compartment syndrome, septic arthritis, infected prosthesis, deep hand infection, periorbital/orbital disease or Fournier’s gangrene.
• Do not perform blind bedside procedures near major vessels, the eye, hand tendon sheaths, genitalia or a prosthetic joint.
• Use aseptic technique, local anaesthesia or procedural sedation only within the practitioner’s competence and monitoring capability.

Special anatomical situations

• Face and periorbital skin: examine vision, eye movements, pupils and pain with movement. Proptosis, reduced vision, ophthalmoplegia, severe headache or toxic appearance suggests orbital involvement and requires emergency admission and specialist review.
• Hand and fingers: assess tendon function, sensation, pulses and passive stretch. Kanavel signs or rapidly progressive swelling need hand-surgery review.
• Foot and diabetes: assess pulses, sensation, ulcers, callus, depth, bone exposure and glucose. Consider osteomyelitis and multidisciplinary diabetic-foot care.
• Perineum: pain, swelling, bullae, crepitus or systemic toxicity may be Fournier’s gangrene; urgent resuscitation and surgery are required.
• Breast or postoperative site: assess for abscess, wound dehiscence, prosthetic infection and need for imaging or surgical drainage.

Sepsis and deterioration pathway

Cellulitis can trigger bacteraemia and septic shock, particularly in older adults, people with diabetes, immunosuppression or extensive infection. Reassess frequently rather than relying on a single reassuring temperature.

1. Recognise abnormal physiology: altered mental state, fast breathing, hypotension, weak pulse, mottling, cold extremities, low urine output or rising lactate.
2. Call for senior help and move the patient to an area capable of continuous monitoring.
3. Obtain IV access, blood tests and cultures if feasible without delaying antibiotics.
4. Give timely antimicrobials and carefully titrated crystalloid for hypoperfusion, reassessing lungs, blood pressure, capillary refill and urine output after each bolus.
5. Escalate for vasopressor and critical-care support if shock persists or fluid is unsafe.
6. Search for source-control needs: abscess, necrotising infection, infected device, septic joint or osteomyelitis.

Nursing interventions

• Record baseline observations, pain score, mental state, lesion location, dimensions, photographs or border markings according to policy.
• Repeat observations at the frequency required by acuity; report new fever, hypotension, confusion, tachypnoea, reduced urine or rapidly expanding erythema.
• Administer antibiotics on time, check allergies, observe for anaphylaxis, document response and maintain IV access.
• Elevate the limb, protect pressure points, change dressings aseptically and assess drainage, odour, colour and tissue viability.
• Monitor intake, output, glucose and renal function, especially during sepsis or IV therapy.
• Provide analgesia and non-pharmacological comfort; reassess effect rather than simply recording administration.
• Support nutrition, hydration, mobility and safe toileting while preventing falls.
• Explain the treatment plan, antibiotic adherence, warning signs and follow-up in the patient’s preferred language.
• Use standard precautions and dispose of contaminated dressings safely; apply additional precautions if drainage is uncontrolled or another transmissible infection is suspected.

Monitoring response to treatment

Admission and discharge decisions

Consider admission when

• There is sepsis, haemodynamic instability, altered mental state or organ dysfunction.
• Infection is rapidly progressive, extensive, bullous, necrotic or associated with severe pain.
• There is facial/periorbital, hand, genital, deep foot, prosthetic-joint or postoperative involvement.
• The patient is immunocompromised, pregnant, very young, frail, unable to take oral medicines or unable to manage wound care.
• Oral treatment has failed, adherence is doubtful or reliable follow-up is unavailable.

Discharge only when appropriate

• Vital signs are stable, pain is controlled and there is no concern for deep infection or sepsis.
• The patient can drink, take medication, elevate/protect the area and return for review.
• A written plan gives the antibiotic name, route, schedule, duration, adverse effects and what to do if a dose is missed.
• A review appointment or safety-net contact is arranged, usually within 24–72 hours depending on severity.

Complications

• Abscess, lymphangitis, lymphadenitis and recurrent cellulitis.
• Bacteraemia, sepsis, septic shock and metastatic infection.
• Necrotising fasciitis, myositis, pyomyositis or compartment syndrome.
• Septic arthritis, osteomyelitis or infected prosthetic material.
• Orbital cellulitis, cavernous sinus thrombosis or intracranial spread from facial infection.
• Chronic lymphoedema, tissue damage, scarring and functional impairment.
• Drug reactions, antibiotic-associated diarrhoea and antimicrobial resistance.

Prevention and recurrence reduction

• Wash minor wounds with clean running water, remove visible dirt and cover with a clean dressing.
• Treat tinea pedis and cracked toe webs; dry carefully between toes and change socks regularly.
• Moisturise eczema-prone skin, avoid scratching and keep nails short.
• Manage diabetes, oedema, venous disease and weight with the appropriate clinical team.
• Use compression for chronic oedema only after arterial circulation is assessed and acute infection has settled.
• Use protective footwear and gloves; avoid walking barefoot where injury risk is high.
• Seek early care for painful, hot, swollen skin rather than applying irritants or delaying treatment.
• For frequent recurrences, look for untreated tinea, ulcers, lymphoedema, venous disease or nasal staphylococcal carriage and discuss specialist prevention.

Scenario-based application

Common errors to avoid

• Calling every red, swollen leg cellulitis without considering DVT, venous stasis or contact dermatitis.
• Failing to inspect the toe webs, wound, perineum, pressure areas or concealed portal of entry.
• Waiting for laboratory confirmation before giving antibiotics to a septic patient.
• Using antibiotics alone for a drainable abscess.
• Delaying surgery because an imaging report is pending when necrotising infection is clinically likely.
• Prescribing broad antibiotics without review, culture interpretation or a stop/step-down plan.
• Ignoring renal function, allergy, pregnancy, drug interactions or local resistance patterns.
• Discharging without a border mark, clear safety-netting and a follow-up plan.

Documentation checklist

• Time of arrival, history, allergies, comorbidities and relevant exposure.
• ABCDE findings, vital-sign trend, pain score, glucose and sepsis screening.
• Exact site, measurements, border marking/photograph, wound description and neurovascular findings.
• Differential diagnosis, investigations, cultures and senior/surgical discussions.
• Drug, dose, route, time, indication, response and adverse effects.
• Wound care, elevation, mobility, intake/output and patient education.
• Disposition, review date, return precautions and responsible clinician.

Quick revision questions

1. How does cellulitis differ clinically from an abscess and from erysipelas?
2. Name six risk factors for cellulitis recurrence.
3. Which findings make you suspect necrotising fasciitis rather than uncomplicated cellulitis?
4. When are blood cultures, ultrasound or advanced imaging useful?
5. What are the first five actions for a patient with cellulitis and septic shock?
6. Why is source control important in purulent infection?
7. What features make facial, hand, perineal or diabetic-foot cellulitis high risk?
8. What information must be included in discharge safety-netting?

Key takeaways

Further reading

• CDC: About cellulitis
• CDC clinical guidance for group A streptococcal cellulitis
• IDSA skin and soft-tissue infection guideline
• NHS: Cellulitis