AIDD Course Back up website: Module 5A Bacterial Skin Infections

Skin infections can be bacterial, viral, fungal, ricketsial and rarely protozoal. The bacterial ones to concentrate on in this module are the common Staph and Strep infections including Impetigo, Folliculitis and Cellulitis. You should also be aware of the Staph scalded skin syndrome and Toxic shock syndrome and never forget the significance of fever, sore neck and a little bit of purpura in a sick child or young adult with Meningococcaemia.

CHAPTER 9 – BACTERIAL INFECTIONS

There is a podcast on this module that you can listen to either before you do the reading of the module or after, whichever you prefer!

Podcast on Bacterial infections of the skin. Just click on the little arrow next to the loudspeaker motif on the left side of the bar to start the podcast.

After listening to the podcast View this video on the images in this Module 5A.

Below is a YouTube version of this video

Most bacterial skin infections will present as pustules, blisters or red nonscaly plaques. Hence the mnemonics are II Infective Inflammatory for pustules or ICI, Infective , Contact or Inflammatory Immunological for blisters. If a red non scaly plaque then CUL DVA EVIE and infections really only directly come up under I for infiltrates of cells or substances with the cells being neutrophils. Rarely with some chronic granulomatous infections such as TB and Deep fungal infections you can have red scaly plaques although most of the inflammation is in the dermis rather than the epidermis.

Staphylococci, Streptococci and Propionibacterium acnes are the main bacterial infections seen in dermatology. Most conditions have a follicular origin and staph folliculitis is one of the commonest conditions that we see. Antibiotic resistance over the last few years is making them an interesting problem.

Impetigo is one of the commonest conditions seen in children. It may present as flaccid pustules or blisters or as crusts. It is virtually always staphylococcal in origin and only occasionally streptococcal. Certain types of staphylococci produce toxins which will allow splitting to occur in the top layers of the epidermis giving a very flaccid blister. Often this will burst and dry and present as a crust. This condition is commonly known as school sores. The complications that may be associated with this condition include acute nephritis which is usually diagnosed by the presence of red cell casts in the urine and is really only seen with the Strep variant.

The prevention of impetigo is important. Staphylococci can survive cold washing. Therefore hot washing of clothes in contact with the skin is necessary. Bactroban or Mupirocin ointment can be used in the nostrils and in other areas of staphylococcal colonisation. The ointment should be applied to any small breaks in the skin surface such as insect bites or cuts and scratches. This is a highly transmissible condition . Also siblings or parents may be Staph carriers and a source of re infection of a child. Hence swab the family if a patient has recurrent impetigo.

Dermnet on Impetigo

Royal Children's Hospital Melbourne Guidelines on cellulitis and other infections

Early intact bullous staph lesion before bursting and crusting.

impetigo on the face. It often originates from around the nose.

Blistering staph infection after using topical steroids on an area of dermatitis.

Ecthyma is a necrotizing infection generally due to B haemolytic streptococci, giving a lesion akin to a cigarette burn with a central eschar. It commonly occurs on the buttocks or thighs of children.A similar type of lesion can be seen with ecthyma gangrenosum due to pseudomonas septicaemia in immunosuppressed patients and from fusarium or mucor fungal infections, again in immune suppressed or diabetic patients.

Diagnosis Eschars are feature of ecthyma, ecthyma gangrenosum, fusarium and mucor fungal infections and rarely from cigarette burns in dermatitis artefacta. An eschar can also be seen in cutaneous anthrax.

Dermnet on Ecthyma

Dermnet on Ecthyma gangrenosum

Also have a look at these images of ecthyma in GlobalskinAtlas

The necrotic surface of ecthyma has sloughed off leaving this ulcer.

pseudomonas and mucor and fusarium infections as the cause in those cases.

Localised skin necrosis from Serratia Marcesens in a patient immunosupressed by myelofibrosis

Cellulitis and Erysipelas are usually due to streptococcal infection. Erysipelas involves the top layers of the skin and is tender, oedematous, sometimes with early blistering and associated with systemic symptoms. Cellulitis is deeper, does not involve the lymphatics directly but may spread via lymphatics to local lymph glands. This is known as lymphangitis. If you see this then septicaemia may follow and follow quickly. Treat with high dose oral or IV antibiotics.

Habif does an excellent section on page 341 on the various presentations of erysipelas and cellulitis in different areas. In children facial cellulitis may be due to H influenzae type B.

Habif also does an excellent section on periorbital cellulitis and perianal cellulitis on page 342. Both of these conditions are due to streptococci. The periorbital one can involve venous drainage to the cavernous sinuses and give rise to a severe cerebral event if it is not treated aggressively, sometimes causing a cavernous sinus thrombosis.

Perianal cellulitis is due to a Group A beta haemolytic streptococcus with quite florid perianal erythema spreading out from the anal opening. It is difficult to pass a bowel motion because of pain. Children with this condition respond to bactroban ointment applied to the area over a three week period better than to oral antibiotics but personally I use both!

Dermnet on cellulitis

Dermnet on Erysipelas

Dermnet on streptococcal perianal cellulitis

Often erysipelas is unilateral but this was a bilateral case.

Cellulitis of the lower leg, red, hot and may show lymphangitis and enlarged groin nodes.

Composite image showing also the streptococcal perianal cellulitis picture in a young child. You might want to diagnose a contact allergy or worm infection but neither look like this!

Necrotizing fasciitis is a rare disorder due to group A streptococci with deep infection resulting in destruction of the fascia and fat. It generally will present with an overlying area of cutaneous necrosis and a black eschar. This is a serious disease in which death can occur. The pain is very severe and seems to be out of proportion to the severity of the apparent illness. This is well described on page 342. Note the loss of surface sensation in the involved area.

Diagnosis A feature of this condition is that the involved skin is insensitive to pin prick because of the depth of the necrotic damage.

Treatment Straight to hospital for IV high dose antibiotics and early surgery to remove devitalised tissue.

Dermnet on Necrotising fasciitis

If you live in the Northern Territory or North Queensland the other condition you have to be aware of is Melioidosis. This is a bacterium in the soil that tends to enter the skin in flood conditions after cyclones when people are injured wading in deep dirty water. It also gives marked skin necrosis but usually presents with a pneumonia first. The skin ulcers have to be widely debrided plus IV antibiotics. Look it up in Dermnet or eMedicine.

Melioidosis - In a descriptive study involving 540 patients in tropical Australia over a 20-year period, the primary presenting feature was pneumonia (in 51% of patients), followed by genitourinary infection (in 14%), skin infection (in 13%), bacteremia without evident focus (in 11%), septic arthritis or osteomyelitis (in 4%), and neurologic involvement (in 3%). Over half of patients have bacteremia on presentation, and septic shock develops in approximately one fifth. Internal-organ abscesses and secondary foci in the lungs, joints, or both are common.

Another unusual infection I sometimes see in my part of the estuarine semitropical world is Vibrio vulnificus infection. People go walking in the river estuaries , get a cut foot or ankle and a cellulitis with rapidly developing eschars and worsening cellulitis.

See This reference for assessment and treatment.You need to swab and do an incisional biopsy of these lesions to diagnose them.

Initially this was thought to be necrotising fasciitis but it turned out to be a necrotising cellulitis.

Note the extent of the swelling.

See other images of this case in GlobalSkinAtlas

Folliculitis is virtually always staphylococcal although rare instances of pseudomonas folliculitis can occur in people who have used a contaminated hot tub. The pustule is centred on a hair follicle but it does not destroy it. Folliculitis is common in friction prone areas including the buttocks. When the infection extends into the local adjacent tissues the lesion is known as a furuncle. When several furuncles combine the lesion is called a carbuncle.

Treatment Use some bactroban mupirocin cream if the staph folliculitis is localised or some dicloxacillin orally if generalised infection. Hot wash clothing and towels. Use an antiseptic wash such as chlorhexidine. Pseudomonas folliculitis is self limiting.

Dermnet on folliculitis

Dermnet on Pseudomonas folliculitis

Pseudofolliculitis barbae is a common problem especially in Negroes and people of Middle Eastern origin where the hairs do not grow straight but with a twist. If they are shaved excessively close to the skin especially with a blade razor then the hair can grow into the skin and cause the equivalent of a foreign body reaction. This topic is well described in page 346 and Habif gives an excellent series of programs in box 9-4 and 9-5 on ways to try and stop this occurring.

Dermnet on Pseudofolliculitis barbae.

Acne keloidalis is a staphylococcal infection of hair follicles at the nape of the neck often giving rise to deep abscesses and keloid scars if it is not treated aggressively.It has already been discussed in the Acneiform eruptions Module 3 part 9.

Excellent summary of Common skin infections Reference Only

Small pustules around hair follicles in staph folliculitis

Pseudomonas folliculitis from an infected hot tub.

Ingrowing hairs giving a foreign body folliculitis

Table 9-7 lists diseases that may manifest as boils. It is useful just to look at this. page 351 There are some rarer diseases especially the immunodeficiency disorders but it is worthwhile knowing that some of them present as boils.

Also read Box 9-6 Eradication of S. aureus nasal carriage. With recurrent folliculitis or boils you should always swab the nares and axillae looking for chronic staph carriage especially when the skin has cleared. Clearing MRSA infection is difficult. In hospital vancomycin is the drug of choice. There is no good evidence for other procedures but sometimes just time away from the source environment coupled with the use of skin antiseptics, nasal mupirocin and salt water and sun exposure at the beach can effect a change in body flora.

Dernet on Boils

Erysipeloid is an acute skin infection caused by Erysipelothrix rhusiopathiae particularly seen in people who handle unprocessed meat such as butchers and fishermen.

Dermnet on Erysipeloid

Blistering distal dactylitis is a rare disease seen in children particularly at the tip of the finger and is due to group A beta haemolytic streptococcus. It is not a common condition. Post streptococcal peeling of the skin may be seen afterwards.

Dermnet on Dactylitis

Panton-Valentine Leukocidin protein Comment from a Colleague on this in Dermo (Reference Only)

PVL +ve Staph aureus has become huge in the US, particularly along the west coast, with San Francisco particularly badly hit. One particular strain of Staph aureus, called USA300, has become the dominant strain in both hospital and the community. They are particularly seeing recurrent skin furuncles. High risk groups there include prisoners, men who have sex with men, children in day care & IV drug users - i.e. (just about everyone in San Francisco!)(I dont think we have anyone from San Francisco taking the course.)

In Australia, it is getting reasonably common although mostly with a different Staph strain. We do see quite a few people with recurrent boils and some of these are PVL +ve. Some really unlucky people get severe necrotising pneumonia or bacteraemias with it. Main risk groups here are IV drug users and Pacific Islander populations, although I had a family last week who all got boils after moving in to a house just vacated by a bunch of drug users. There is also a theory that animals such as dogs may get colonised and may help maintain this bug in some households."

At the meeting in London they seemed to be indicating that all those non-MRSA staph patients with appalling folliculitis that seems to respond and then flares again when given sensitive antibiotics (Fluclox, Keflex) should be tested for this PVL and then if positive hit them with two antibiotics at one time; ie clindamycin (to inactivate the protein production) and another (fluclox etc)

Erysipeloid of the hands of a fisherman.

Erysipeloid at the knee

An unusual but distinctive and painful Strep infection in children

The staph scalded skin syndrome is certainly one of the great infectious diseases of dermatology and important to recognise. For may years it was thought to be one of the variants of toxic epidermal necrolysis until it was realised that a toxin producing staphylococcus causes very superficial blistering of the skin with the rest of the epidermis being normal whereas in Toxic epidermal necrolysis there is full thickness epidermal necrosis. This section is well dealt with from page 355 of Habif and you should read all of this.

Dermnet on the Staph scalded skin syndrome

Toxic shock syndrome (Reference Only)

Toxic shock syndrome is a worrying condition to diagnose and manage. It is likely to present to you as an ill young woman with high fever, headaches, myalgias, generalized redness and features of septicaemia and shock . The condition developes quickly because it is due to a toxin producing bacteria, either specific serotypes of Staphylococcus aureus or Streptococcus pyogenes. In a Staph producing case the source of infection is likely to be an infected retained tampon and the condition flares within a few days of menstruation. Strep induced toxic shock usually arises from a skin infection but it is usually a severe one such as a deep soft tissue injury or necrotizing fasciitis. Only about 20-30% of toxic shock cases are not due to retained tampons. They can be seen after burns, or surgical procedures but generally only in patients with predisposing local tissue factors or other medical illnesses that predispose them to infection. They fail to produce any antitoxin antibodies which renders them susceptible to rapidly succumb to this condition.

The initial skin finding is a scarlatiniform rash mainly on the trunk but spreading rapidly elsewhere, with marked conjunctival redness and oedema of the hands and feet. Later on you get marked peeling of the skin on the hands and feet but this is in the recovery phase and is typical of a streptococcal origin for the infection.

The patient’s initial presentation could suggest the Staph scalded skin syndrome but in toxic shock the patient is more unwell. A skin biopsy is not diagnostic but it helps to rule out that other differential of toxic epidermal necrolysis where there is full thickness skin necrosis or a drug hypersensitivity syndrome.

Treatment is early admission to hospital for general medical care, IV hydration and antibiotics and treatment of any other areas of organ failure. Speed is of the essence in treating this condition. If there is a retained tampon it should be removed. Deep soft tissue infections should be surgically decompressed and necrotizing fasciitis surgically cleared to remove the source of the toxin.

Dermnet on Toxic shock syndrome

Diffuse red tender skin in a neonate with Staph scalded skin

Later stage of SSS after peeling

Sub corneal split high in epidermis from toxin in Staph scalded skin.

From page 358 Habif deals with pseudomonas infection. It can present as a folliculitis or as a hot foot syndrome and rarely as cellulitis. It is often a secondary contaminant of an ID reaction between the toes due to a fungal infection and again it is often seen along with proteus in the external ear canal when someone spends a lot of time in the water and the ear is continually wet. There is a very good section on this on page 362. This is a common problem in general practice and it is useful to know how to treat it. Use dilute acetic acid soaks (one part vinegar to 3 parts water)

Ecthyma gangrenosum is another rare manifestation of pseudomonas septicaemia presenting similar to streptococcal ecthyma with a necrotic area in the skin but it has a much greater risk of death. As it represents pseudomonas septicaemia blood cultures will pick this up. Again it will be seen in an immunosupressed patient (HIV, high steroids, immune supressing drugs, Biologics)

Dermnet on ecthyma gangrenosum in case you missed it the last time!

GlobalSkinAtlas images of ecthyma gangrenosum

Early lesions of Pseudomonas septicaemia. The blisters burst and then a necrotic eschar forms of ecthyma gangrenosum.

This is another case showing the eschar.

Pseudomonas as a gram negative infection in bullous tinea Use vinegar soaks.

Meningococcemia is another one of the major infectious diseases that we are seeing more and more of or at least it is being reported more in the popular press. People become ill and die very quickly due to a form of disseminated intravascular coagulation due to septicaemic shock. This is described well on page 299 and you would be well advised to read this section several times. Always think of it in a child who has a fever, sore neck and even just one or two small petechial spots in the skin. It is important to treat this sort of patient early with IM injections of third or fourth generation cephalosporins without waiting for any necessary cultures then ship them off to Emergency Outpatients.

Dermnet on meningococcaemia

Habif ends up this chapter on the non-tuberculous or atypical mycobacteria. These are rare conditions usually seen as a granulomatous lesion on the hand in people who keep fish as a hobby and the organism involved is mycobacterium marinum. Minomycin is the treatment of choice for two to three months. This topic is discussed on page 375. Note also the ulcerating type of atypical mycobacterial infection due to Mycobacterium ulcerans. The latter is one of the few infective diseases best treated by surgical excision. We look at atypical mycobacteria in the deep fungal chapter because Sporotrichosis with lymphatic spread is the main DD.

Dermnet on Atypical mycobacteria