Cellulitis

19 Jul

A short-term bacterial infection that affects the skin and under the skin tissue (subcutaneous) which causes painful, warm, red, swollen skin. The bacteria involved in this condition are most likely either streptococcus pyogenes or staphylococcus aureus.

- Affects over 14 million cases in the US annually [1]
- 0.2 to 24.6 per 1000 person-years (types of measurement that take the number of people in the study and the amount of time each person spends in the study) [2]
- The incidence of cellulitis is approx 200 cases per 100,000 individuals globally [3]
- Cellulitis commonly affects middle-aged and older people [4]
- Cellulitis affects approximately 1 in 40 people per year [5]
- The bacteria that causes cellulitis exists on the skin usually but when it enters the layers under the skin- it can be harmful and cause an infection.
- Infection sites can be created by:
- Cuts/grazes
- Burn
- Animal/human/insect bites
- Puncture wound
- Leg ulcers
- Dry and cracked skin eg eczema, athlete’s foot etc.
- Surgical wounds [7,8]
Medical Student
- Common causative organisms:
  - Streptococcus pyogenes
  - Staphylococcus aureus
- Entry point:
  - Via breaks in the skin barrier (e.g. trauma, cracked skin, surgical wounds)
- Pathogen progression:
  - Bacteria enter the wound site
  - May overwhelm local immune defences, depending on patient risk factors
  - Can spread:
    To lymphatic system (lymph nodes)
    Or via blood vessels to distant sites
- Systemic spread:
  - May reach endocardium or bone, causing deep infections
- Immune response:
  - Pathogen triggers inflammatory cytokines
  - Causes:
    Local inflammation: redness, warmth, pain, swelling
    Pus formation: accumulation of bacteria, immune cells, and dead tissue
    Systemic inflammation: fever, chills, malais
Patients
- Bacteria can enter the body through broken skin (cuts, cracks, wounds, surgery)
- Once inside, the bacteria can:
  - Spread to lymph nodes or
  - Travel through the blood to other parts of the body
- The bacteria may reach deeper areas like the heart or bones
- This causes your body to react with inflammation, leading to:
  - Fever, chills, and feeling unwell
  - Redness, warmth, swelling, and pain at the infected area
  - Pus build-up (a mix of bacteria and dead cells)
- The body fights the infection using natural substances that cause these symptoms as part of the healing process [6]
- Breakage in the skin
- Leg oedema
- Venous insufficiency/ surgery
- Obesity
- Pregnancy
- Conditions that increase the risk of infections (eg. diabetes Mellitus, immunocompromised conditions, liver or renal disease)
- Chickenpox
- Alcohol abuse
- Increased age
- Lymphadenectomy (lymph nodes are removed) [2]
- Tenderness of the skin
- Warmth
- Swelling (oedema)
- Peau d’orange (resembles the skin of an orange on the skin)
- Patches of skin (petechiae)
- Fever
- Chills
- Fast heartbeat (tachycardia)
- Headache
- Low blood pressure (hypotension)
- Delirium in severe infections (confusion caused by infections)
- Pain
- Nausea and vomiting in severe cases [7,9]
- Eron classification system (categorised from Class 1- no signs or co-morbidities to Class 4- sepsis or life-threatening infections)
- Take a history of symptoms, recent trauma, underlying conditions and risk factors for cellulitis.
- Examining the person for obvious skin breakages, and presentation of the skin (redness, warmth, edges etc).
- Investigations such as blood tests, skin biopsies and swabs are not always necessary for diagnosis.
- Tissue culture should be strongly considered for the identification of the causative organism because of the increased risk of fungal infection. [2,7]
- Erysipelas (skin infection affecting the skin)
- Necrotising fasciitis or gas gangrene (severe wound infection)
- Varicella zoster (eg. chickenpox)
- Septic arthritis
- Bursitis (inflammation of fluid-filled sacs between tissues of the body)
- Gout (inflammation of the joint in the big toe)
- Insect bites eg Lyme disease [10]
Medical Student
Lifestyle Measures
- Immobilise and elevate the affected area to reduce oedema
- Cool, wet dressings to reduce local inflammation and pain
Uncomplicated Cellulitis (Eron Stage 1–2)
- Oral antibiotics:
  - Dicloxacillin or Cephalexin
  - Penicillin allergy: Clindamycin
After Animal Bite
- First-line: Amoxicillin–clavulanic acid
- Penicillin allergy: Clindamycin + oral fluoroquinolone or sulfamethoxazole/trimethoprim (double strength)
After Water Exposure
- Fresh/brackish water: Cephalexin or Cefazolin + fluoroquinolone
- Salt water: Doxycycline
Recurrent Cellulitis (≥3–4 episodes)
- Benzathine penicillin
- Erythromycin
- Penicillin V
Complicated Cellulitis (Eron Stage 3–4) / MRSA Suspected
- Oral treatment options:
  - Sulfamethoxazole/trimethoprim
  - Doxycycline
  - Linezolid
  - Clindamycin
- IV/severe cases (secondary care):
  - Vancomycin
  - Linezolid
  - Daptomycin
  - Teicoplanin
Patients
Self-Care Tips
- Keep the affected area raised and try to rest it
- Apply a cool, damp cloth to reduce swelling and heat
- Monitor symptoms and take all medications as prescribed
Mild Cellulitis
- Can be treated with oral antibiotics:
  - Dicloxacillin or Cephalexin
  - If allergic to penicillin, Clindamycin is an option
If Caused by Animal Bite
- You may be given amoxicillin with clavulanic acid
- If allergic, your doctor may combine two other antibiotics
If Caused by Water Exposure
- Fresh/brackish water: treated with cephalexin or other suitable antibiotics
- Saltwater: may be treated with doxycycline
Repeated Infections
- You may be offered long-term antibiotics like penicillin to prevent it from coming back
Serious or Resistant Infections
- If the infection is more severe or doesn’t get better with tablets:
  - You may need stronger antibiotics in hospital (e.g., vancomycin)
  - These are usually given by drip
- Infections caused by resistant bacteria (like MRSA) need special antibiotics [7]
- Uncommon but serious
- Blood infections are known as bacteremia
- Suppurative arthritis (infection in the joint)
- Osteomyelitis (bone infection)
- Endocarditis (inflammation of the layer of the heart)
- Tissue death (gangrene) [8,11]
- Skin that is red and swollen is definitely cellulitis
- All skin and soft tissue infections require antibiotics
- Cellulitis in hospitals is always associated with MRSA
- All patients with insect bites and redness have cellulitis
- If redness extends the original borders of cellulitis, it always means it’s getting worse
- Repeat infections will not happen when someone is taking antibiotic medication [12,13]
- How might I have gotten this infection?
- How long does treatment need to start working?
- How do I manage treatment if I’m already taking medications?
- Are there any alternatives to current medications?
- How can I prevent repeat infections?
- American Academy of Dermatology
- Alberta
- Centres for Disease Control and Prevention
[1] https://www.ncbi.nlm.nih.gov/books/NBK549770/
[2] https://cks.nice.org.uk/topics/cellulitis-acute/background-information/prevalence/
[3] https://academic.oup.com/bjd/article-abstract/157/5/1047/6641438?redirectedFrom=fulltext&login=false
[4] https://pubmed.ncbi.nlm.nih.gov/31747177/
[5] https://pubmed.ncbi.nlm.nih.gov/16490133/
[6] https://calgaryguide.ucalgary.ca/cellulitis/
[7] https://www.nhsinform.scot/illnesses-and-conditions/skin-hair-and-nails/cellulitis#causes-of-cellulitis
[8] https://www.cdc.gov/groupastrep/diseases-public/Cellulitis.html#cellitis-causes
[9] https://www.msdmanuals.com/en-gb/professional/dermatologic-disorders/bacterial-skin-infections/cellulitis?query=cellulitis
[10] https://www.obgproject.com/2021/09/05/cellulitis-clinical-presentation-differential-diagnosis-and-treatment/
[11] https://www.hopkinsmedicine.org/health/conditions-and-diseases/cellulitis
[12] https://lymphoedemaeducation.com.au/resources/top-10-myths-regarding-diagnosis-treatment-cellulitis/#:~:text=Myth
[13] https://journalfeed.org/article-a-day/2017/ten-cellulitis-myths-busted/