Cellulitis and erysipelas: Management of Infection for Primary Care

Summary

Cellulitis is an acute bacterial infection of the lower dermis and subcutaneous tissue. Erysipelas is a more superficial infection which affects the upper dermis.

Both present with similar features. Other inflammatory and non-infective conditions may present with similar features and should be considered before prescribing antibiotics. Secondary bacterial infection may complicate underlying skin conditions.

The commonest bacterial causes of cellulitis/erysipelas are group A streptococci and staphylococcus aureus (including MRSA).

Non-antibacterial management includes elevation, marking edge of area to monitor for spread, analgesia, management of co-existing skin conditions eg venous eczema, fungal infections.

Note: flucloxacillin and co-amoxiclav are not active against MRSA. If patient has a history of MRSA colonisation, risk factors for MRSA or has grown MRSA from pus/wound swabs, use antibiotics guided by culture results if available, otherwise doxycycline (adult, not pregnant) or a macrolide as above are suitable empiric options. See MRSA guideline ID 2258.

Note: flucloxacillin and co-amoxiclav are not active against MRSA. If patient has a history of MRSA colonisation, risk factors for MRSA or has grown MRSA from pus/wound swabs, use antibiotics guided by culture results if available, otherwise a macrolide (clarithromycin or erythromycin) or clindamycin as above are suitable empiric options. Doxycycline should not be used in children under 12 years old or in pregnancy. See MRSA guideline ID 2258.

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Duration of antibiotics

5-7 days. A longer course length (up to 14 days in total) may be needed based on clinical assessment. Note: skin changes may not return to normal for some time and full resolution of symptoms at 5 to 7 days is not expected.

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Footnotes

Microbiological assessment
A microbiological diagnosis of cellulitis is often not possible. If there is no wound/skin break, pus or discharge to swab, a skin swab is unlikely to identify the microbiological cause of the cellulitis. If there is a wound, pus or discharge, send a swab for microbiological culture and sensitivity if there is a penetrating injury, there has been exposure to a water-borne organism or the infection was acquired outside the UK, or if there has been no response to empirical treatment.

Microbiological interpretation
A number of bacteria may be found on a skin swab. The common bacteria are listed below along with their significance. They are group into pathogens, bacteria which are likely to be causing cellulitis when this has been clinically diagnosed, and colonisers, these are unlikely to be causing cellulitis. Pathogens can colonise the skin so their identification must be correlated with a clinical diagnosis of infection before treating the patient. Colonisers can also cause infection in some circumstances e.g. immunosuppression, vascular disease. Treating of colonisers should not be completed unless there is a risk factor for infection with these bacteria and a patient has failed empirical therapy against the pathogen group.

Pathogens
Staphylococcus aureus: is a common cause of cellulitis. It can though colonise the skin so treatment should not be initiated because it is identified in a microbiology sample unless there is clinical evidence of infection.

Group A streptococcus (S. pyogenes): is the most common cause of cellulitis. It can though colonise the skin so treatment should not be initiated because it is identified in a microbiology sample unless there is clinical evidence of infection. 

Colonisers
Skin flora: These include coagulase negative staphylococci, diphtheroids and propionibacteria. These are skin commensals and are not causes of cellulitis.

Enteric flora: These include E. coli and Klebsiella spp. It is common for wounds to become colonised with these bacteria. They are rarely a cause of cellulitis. If a patient has not responded to empirical antimicrobial therapy and these bacteria are cultured as the predominant organism, i.e. reported as the predominant organism and not as mixed enteric flora, please discuss with a Microbiologist if you are considering treatment.

Pseudomonas: P. aeruginosa is a common coloniser of the skin, especially moist wounds. It is an uncommon cause of cellulitis except with predisposing conditions e.g. immunosuppression/vascular disease. It may be associated with puncture wounds (eg standing on a sharp object, body piercings, hand injuries). Treatment for P. aeruginosa is not routinely indicated. If a patient has failed to respond to empirical therapy for cellulitis and has a risk factor for infection and it has been isolated as a predominant organism in culture please contact Microbiology to discuss treatment.

Anaerobes: Anaerobes are a common coloniser of wounds. This colonisation can result in an unpleasant wound smell which can be treated with topical metronidazole. They are not common causes of cellulitis in isolation but if felt to be causing soft tissue infection can be treated with oral metronidazole in addition to standard therapy for cellulitis.

Sensitivities available on request
Some bacteria are uncommon causes of skin and soft tissue infection. We do not routinely release sensitivities for these bacteria to prevent overuse of antibiotics. If you would like to treat a patient whose sample has grown one of these uncommon causes of skin and soft tissue infection please contact Microbiology on (0113) 392 3962 or 07825 906030.

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Background Information

Cellulitis is an acute bacterial infection of the lower dermis and subcutaneous tissue. It presents as a localised enlarging area of red, hot, swollen, tender skin, with systemic symptoms. It is most commonly caused by group A streptococcus (Streptococcus pyogenes) or Staphylococcus aureus (including MRSA). It is most common on the lower leg but can occur on other body sites, and there may be associated lymphangitis, a red streak along lymphatic vessels. Local lymph nodes may be tender and enlarged.

Similar symptoms are seen with erysipelas, a more superficial infection which affects the upper dermis and extends into the superficial cutaneous lymphatics.  It presents with an intense, oedematous, sharply demarcated rash (St Anthony’s fire) and is almost always caused by Group A streptococcus, sometimes there is co-infection with staphylococcus aureus. Erysipelas often presents abruptly and is usually diagnosed by the characteristic rash, usually on the lower limbs but may be on the face, with a butterfly distribution on cheeks/bridge of nose. It often occurs in nappy area/umbilicus in infants.

The diagnosis of cellulitis is clinical based on local signs (eg redness, heat, blistering, peau d’orange, ulceration, abscess formation) and systemic signs (fever, rigors/chills).  It is usually unilateral, bilateral disease is rare and usually due to another condition (eg lymphoedema). It may occur as a complication of an underlying skin condition or wound/injury.

Several conditions may mimic cellulitis, such as lymphoedema (erythema, non-pitting oedema), eczema or dermatitis (may be atopic, contact, venous), fungal infection, DVT (not erythematous), thrombophlebitis (linear, non-oedematous inflammation that follows the course of the underlying thrombosed tender, palpable vein), drug eruptions, psoriasis, lipodermatosclerosis (acute may be red and tender with variable oedema), radiotherapy damage, insect bites/stings. Systemic symptoms/signs of infection in these conditions are not usually present (unless there is secondary infection).Venous disease of the lower legs is a very common cause of red legs and may cause swollen legs. Venous eczema is not usually as hot, red or oedematous as cellulitis. Small vessel vasculitis may present with erythematous skin lesions that are painful. It usually affects both lower legs and there may be ulceration, blistering and mild systemic symptoms such as fever. It is distinguished from cellulitis by the presence of multiple non-blanching lesions.

Risk factors for cellulitis/erysipelas include previous episodes of cellulitis/erysipelas, skin breaks in feet/toes (eg athlete’s foot, tinea pedis or cracked heels), chronic skin conditions such as psoriasis, eczema, venous eczema/ulceration, lymphoedema, skin injury (surgery/trauma/wounds, radiotherapy), immunodeficiency (HIV, diabetes, obesity, alcoholism), pregnancy, chronic liver/kidney disease.

Complications of cellulitis include bacteramia/sepsis, necrotising fasciitis and infective endocarditis.

Rare bacterial causes of cellulitis include Pseudomonas aeruginosus (usually associated with puncture wounds), Haemophilus influenza (children with facial cellulitis), anaerobes, viridans streptococci and Eikenella  from human bites, Pasteurella multicoda from cat or dog bites, Vibrio vulnificans (saltwater exposure), Aeromonas hydrophilia (fresh or saltwater exposure), Erysipelothrix rhusiopathiae (caused by direct contact with infected meat/fish via skin breaks, seen in butchers, abbatoir workers etc).

Necrotising fasciitis is a bacterial infection of the subcutaneous tissues that does not involve the epidermis or upper dermis, and may lead to rapid, severe tissue necrosis. Presentation is usually subtle but severe pain disproportionate to clinical signs, tenderness beyond the erythematous area, crepitus, blistering, fluctuance and rapid progression are seen. Necrotising fasciitis is a life-threatening condition. Urgent surgical debridement is required.

Herpes zoster (shingles) may present with similarities to cellulitis but will have a dermatomal distribution and vesicles. Herpes Zoster (Shingles) in Primary Care ID 2264

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Recurrent cellulitis

Optimise underlying risk factors where possible. Avoid trauma (eg wear long-sleeved/full legged clothing for protection), keep skin clean and well moisturised, elevation of swollen limbs at rest (improves lymphatic circulation), compression dressings for lymphoedema. Chronic suppressive antibiotics may rarely be indicated (low-dose penicillin or erythromycin, guided where possible by previous microbiology results and antibiotic use/response) in high-risk adults, where patients have had 2 or more episodes requiring hospitalisation/specialist advice. Consider severity of previous episodes and risk of complications in decision to trial suppressive antibiotics. Give advice about possible side-effects of long-term antibiotics and to seek medical help if develop cellulitis/erysipelas while on suppressive antibiotics. Use of suppressive antibiotics should be reviewed at least every 6 months, considering success/failure, resolution of underlying risk factors. Stop current suppression if cellulitis/erysipelas occurs on it, consider change of agent.

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