Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Cellulitis

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In one line

·Bacteria are growing in the skin layers (dermis and the fat tissue just beneath it).

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Normal physiology

·Your skin has three layers: the thin outer epidermis, the thicker dermis (full of blood vessels, nerves, and immune cells), and the subcutaneous fat layer underneath. Lymphatic vessels drain fluid and trapped germs to lymph nodes, which filter them out. Immune cells patrol constantly and kill bacteria that sneak through tiny breaks. This keeps you safe every day.

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What goes wrong

·A break in the skin lets bacteria in. The two most common bacteria are Streptococcus (strep) and Staphylococcus (staph). Strep spreads fast through the lymphatic vessels. Staph tends to form pus pockets (abscesses). Anything that damages the skin or weakens the immune system makes cellulitis more likely: cuts, scrapes, bug bites, athlete's foot, eczema, IV drug use (needles poke holes), diabetes (high blood sugar slows immune cells), lymphedema (swollen limbs from bad lymphatic drainage), and venous insufficiency (blood pools in the legs and the skin gets fragile).

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Hallmark signs

·Warm, red, tender skin that spreads out without a clear border
·Swelling of the infected area
·Pain and tenderness when you press on the area
·Warm skin over the red area
·Sharp, clear edge to the redness (suggests erysipelas, a type of cellulitis closer to the surface)
·Fever and chills
·A soft, squishy spot under the skin (fluctuance)
·Pain that feels much worse than the redness looks

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Red flags · escalate now

·Pain that is far worse than what you see on the skin (may signal necrotizing fasciitis, a fast-moving infection that destroys muscle and tissue)
·Purple or black patches, blisters filled with blood, or skin that feels numb (signs tissue is dying)
·Fever over 100.4°F with confusion, very fast heart rate, or feeling faint (signs bacteria may be in the bloodstream—sepsis)
·Swelling that spreads quickly over hours (suggests aggressive infection needing urgent treatment)
·A pocket of pus (abscess) that needs drainage, not just antibiotics

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Workup

·Complete blood count (CBC) with differential
·C-reactive protein (CRP)
·Blood cultures (two sets from different sites)
·Wound culture or aspirate from the leading edge of redness (if pus-filled (purulent))
·Ultrasound of the swollen area
·Creatine kinase (CK) level — if severe pain or concern for necrotizing infection

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Treatment

·Find the break in the skin (wound, athlete's foot, eczema, IV site) and classify cellulitis as pus-filled (purulent) (with pus or abscess) or non-pus-filled (spreading redness only)
·Non-pus-filled (purulent) cellulitis: give cephalexin 500 mg by mouth four times a day, or cefazolin 1–2 g IV every 8 hours (IDSA 2014)
·Pus-filled (Purulent) cellulitis or suspected MRSA: give clindamycin 300–450 mg by mouth three times a day, doxycycline 100 mg twice a day, trimethoprim-sulfamethoxazole (TMP-SMX) 1–2 double-strength tablets twice a day, or vancomycin 15–20 mg/kg IV every 8–12 hours (IDSA 2014)
·Drain any fluctuant abscess with needle aspiration or surgical incision and drainage
·Elevate the affected limb above the level of the heart and apply cool compresses
·Treat the underlying skin break: antifungal cream for athlete's foot (tinea pedis), moisturizer and steroid cream for eczema, compression stockings for venous insufficiency
·Admit to hospital for IV antibiotics if patient has systemic toxicity (high fever, low blood pressure, confusion), failed outpatient treatment, or cannot take pills

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NCLEX trap

·Antibiotics kill bacteria. But if you do not fix the break in skin, cellulitis comes right back. Always ask: what let the bacteria in? Treat that too. For example, if athlete's foot cracked the skin, you need antifungal cream too.
·Non-pus-filled (purulent) cellulitis is usually strep (a bacteria that lives on skin) — use cephalexin or cefazolin. Pus-filled cellulitis (has pus or abscess) is usually staph including MRSA (a resistant bacteria) — use clindamycin, doxycycline, or vancomycin. Ask: is there pus? The answer changes your antibiotic.
·Necrotizing fasciitis is a surgical emergency. If pain is much worse than the exam looks, or if there is crackling under the skin or blistering, call surgery right now. Antibiotics alone will not save this patient. Surgery must cut away dead tissue fast.
·An abscess (walled-off pocket of pus) needs drainage. Antibiotics cannot reach pus that is walled off by the body. Drain it first, then antibiotics work. Think of it like a locked room — medicine cannot get in until you open the door.
·A diabetic foot with cellulitis needs wider antibiotic coverage like piperacillin-tazobactam or a carbapenem because more types of bacteria can be involved. Risk factors change the bugs and the treatment. Know the patient's story.
·Lifting the limb helps the body drain the swelling and fight infection. It is a simple tool that works. Antibiotics plus elevation is better than antibiotics alone. Gravity helps fluid move out of the infected tissue.

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