Skin and Soft Tissue Infections

Question 1

What are the symptoms of cellulitis?

Answer 1

• Pain
• Warmth
• Swelling
• Erythema
• Blisters and bullae
• Fever, malaise, nausea and rigors may accompany or precede skin changes

Question 2

What causes cellulitis?

Answer 2

Develops when microorganisms (most commonly streptococcus pyogenes and staph aureus) gain entry to dermal and SC tissues via disruptions in cutaneous barrier.

Question 3

What are risk factors of cellultis?

Answer 3

• Skin trauma
• Ulceration
• Obestity
• People with venous stasis or lymphoedema are at higher risk of cellulitis in the legs e.g. secondary to CHF or patients who are obese and have excess adipose tissue on their limbs and trunk
• Diabetes

Question 4

What are complications of cellulitis?

Answer 4

• Necrotising fasciitis
• Sepsis
• Persistent leg ulceration
• Recurrent cellulitis - common and each episode increases the likelihood of subsequent recurrence

Question 5

What are the differentials for cellulitis?

Answer 5

• DVT
• Septic arthritis
• Acute gout
• Ruptured Baker’s cyst
• Lymphoedema
• Venous insufficiency
• Venous eczema

Question 6

What do you need to look out for in cellulitis?

Answer 6

The hands have small spaces, swelling can cause compression quickly in the hand and especially fingers. This can lead to nerve and blood supply damage. Therefore, it is important to assess sensation and CRT. If there is any concern regarding the neurovascular integrity of an infected hand, this is an orthopaedic emergency and the patient should be admitted for IV abx and debridement.

Question 7

What is the treatment for cellulitis?

Answer 7

• Flucloxacillin is 1st line abx for cellulitis most likely caused by staph aureus and streptococci - very active against staph aureus
• Co-amoxiclav would cover normal, susceptible staph and strep but its spectrum is otherwise unnecessarily broad
• Clarithromycin PO is appropriate for uncomplicated cellulitis in patients with penicillin allergy
• Piperacillin with tazobactam would also work but it has an even broader spectrum of activity - best practice to give as narrow spectrum abx as possible in order to reduce the chance of resistance and abx-related diarrhoea
• Fusidic acid can be given as a topical treatment for impetigo
• Clindaymcin can be used in patients allergic to penicillins - however, it is strongly associated with C.diff associated diarrhoea (active against most gust anaerobes except for C.diff)

Question 8

What needs to be considered with an animal or human bite?

Answer 8

• Dog, cat and human bites need to be treated slightly differently because infection is usually polymicrobial. Mouths are full of variety of bacteria and a bite usually inoculates more than one of these.
• A wound can be contaminated with tetanus spores if it is dirty, has been contaminated with saliva or is a deep puncture wound. Need to check if the patient’s tetanus immunisations are up to date.
• If a patient has been bitten by a dog outside of the UK need to consider giving the rabies vaccine +/or immunoglobulin

Question 9

What is the treatment for cellulitis from a dog bite?

Answer 9

• Co-amoxiclav 1st line for mammal bites
• Clarithromycin can be used in uncomplicated cellulitis in patients with a penicillin allergy but is not ideal for bites
• Flucloxacillin will not cover the anaerobes from the bite, it is best for MRSA and strep infections
• Vancomycin is used IV to treat severe MRSA soft tissue infections. It does not become absorbed when taken orally but oral vancomycin can be used for GI infections such as C.diff diarrhoea.

Question 10

What antibiotics are good for MRSA?

Answer 10

• Vancomycin and doxycycline are both normally active against MRSA. Doxycycline is more suitable for mild-moderate infections. Other abx are linezolid and teicoplanin.
• Ceftriaxone, clarithromycin and meropenum - no activity against MRSA

Question 11

MSSA vs MRSA

Answer 11

Staph aureus is classified into MSSA and MRSA. MRSA is no more virulent than MSSA but it is difficult to treat as it is resistant to all penicillins, cephalosporins and many other 1st line abx. It can cause superficial infections such as boils and impetigo or more serious infections, such as deep surgical site infections. The antimicrobial treatment relies on abx that have many SEs and are more expensive. It is usually hospital-acquired and also can be community-acquired.

Question 12

How does MRSA commonly spread and what are the risk factors?

Answer 12

Mostly by direct physical contact between people. It can also be spread via fomites e.g. towels, sheets, dressings and stethoscopes. Risk factors for MRSA colonisation include recent courses of abx, hosp admissions, open wounds and contact with someone with MRSA.

Question 13

Where does staph aureus colonisation usually occur?

Answer 13

The skin, most commonly in the nose, armpits, groin and wounds.

Question 14

What is done to help prevent the spread of MRSA?

Answer 14

Patients are often screened for MRSA colonisation via a swab when they are admitted to hospital or pre-operatively. Topical treatment to eradicate MRSA is available with washing lotions, creams, nasal ointment or powders. Vancomycin is appropriate for moderate to severe MRSA infection

Question 15

What is asymptomatic bacteriuria?

Answer 15

Many elderly patients >65 yrs may culture bacteria from their urine. When there are no signs or symptoms of a UTI this is asymptomatic bacteriuria and is an example of colonisation. E.coli is the most common bacteria identified. In non-pregnant women and men this is not usually treated.

Question 16

Where does candidaemia spp colonise?

Answer 16

• Normal part of gut flora
• Common colonisers of the oral cavity and vagina as well as moist areas of skin
• Can take advantage of disruption to the skin (line) or mucosal (GI tract) barrier or impaired immunity and cross into bloodstream and establish candidaemia.

Question 17

What are common in IV drug users?

Answer 17

Patients who inject into their groins may have groin sinuses, abscesses and in extreme cases false aneurysms of their femoral and branchial arteries as their peripheral limb veins disappear and they start to use larger veins. Venous insufficiency in the lower limbs causes chronic venous ulcers to develop which commonly become infected secondary to poor hygiene and ulcer care.

Question 18

What blood tests should be done when suspecting a deep soft tissue infection?

Answer 18

• FBC, U+Es, LFTs, clotting, lactate, CRP
• Blood cultures
• ABGs - potential metabolic acidosis secondary to sepsis
• Creatinine kinase (CK) - released from muscles as they break down and this is therefore a marker of severe muscle damage
• XR - some bacteria produce gas which will show as air spaces in the soft tissue on the XR, gas gangrene is an emergency
• USS: can assess the depth of infection and look for collections of pus i.e. abscesses
• ECG: if tachycardic, consider endocarditis
• BBV screening i.e. hep C, B and HIV

Question 19

What is gas gangrene?

Answer 19

Usually caused by clostridium perfingens. It is rapidly progressive and life-threatening. Wounds become contaminated with clostridium spores and the incubation period is usually 2-3 days. Management is similar to necrotising fasciitis with surgical debridement and abx to cover the most likely bacteria.

Question 20

What is necrotising fasciitis?

Answer 20

Cellulitis can lead to necrotising fasciitis (medical emergency). The hallmark of this disease is rapid progression and tissue necrosis, often following trauma or surgery. Infection has spread along the fascial planes and systemic illness is the norm. The patient will need emergency surgical debridement of all necrotic tissue and abx to cover all bacteria. Infection is often polymicrobial and the most commonly isolated bacteria are Group A streptococcus, staphylococcus aureus and anaerobes.

Question 21

What is the treatment for necrotising fasciitis?

Answer 21

Debridement is the only curative treatment, if the patient is too unstable to go to theatre they need resuscitation and surgical debridement ASAP unless they necroted, infected tissue is removed they will not survive. Abx are only supportive.

Question 22

What other things should be looked for in patients with cellulitis in the legs?

Answer 22

Examined for athlete’s foot or fungal nail infection, which can provide a portal of entry for bacteria and should be treated concurrently.

Question 23

What are the commonest bacteria in skin and soft tissue infections?

Answer 23

Staph aureus and strep pyogenes, also know as Group A strep. Other streptococci such as group C and G strep may also cause infection. These bacteria are skin commensals but may become pathogenic if there is a break in the skin which allows them to enter the tissue below. Pseundomonas aeruginosa is associated with hospital-acquired infections and chronic wounds e.g. chronic leg ulcers or diabetic foot ulcers.

Question 24

What is used to treat severe cellulitis?

Answer 24

Surgical interventions are sometimes required for drainage and decrease of pressure. In patients with complicated cellulitis and poor wound healing capacity surgical opinion is always recommended. Cellulitis can spread very rapidly and always needs close follow-up.