Earn up to 3 free CEUs Dermatology Leader in digital CPD for Southern African healthcare professionals Primary bacterial skin infections Introduction Primary bacterial skin infections are sometimes viewed as mere nuisance conditions relative to other graver infectious diseases. However, recognition of these infections is important given their high prevalence, particularly in low-income contexts, and because most can be resolved with appropriate treatment, to the significant benefit Dr Francois de Goede of personal and public health.¹ Bacterial skin infections are classified according to Dermatologist the extent to which the infection penetrates into the subcutaneous tissue, and Panorama Medical Centre, whether associated structures such as hair follicles and lymphatics are affected.² Cape Town They are broadly grouped into skin and soft tissue infections, and acute bacterial skin and skin structure infections. This article focuses on three of the most common and relatively superficial of the former: impetigo, folliculitis and the minor skin abscesses known as furuncles and carbuncles. KEY MESSAGES • Recognition of primary bacterial skin infections is important given their high prevalence and mostly good response to treatment High prevalence and moderate morbidity • Impetigo, folliculitis, furuncles and carbuncles are among the most common skin infections of primary bacterial seen in clinical practice infections warrants • Staphylococcus aureus and Streptococcus pyogenes are the main causative agents their being made a public health • Primary infections are generally mild and treated with topical antibiotics; more severe cases require oral antibiotics priority • Carbuncles and larger furuncles usually require incision and drainage • Bacterial culture swabs should be done for persistent or recurrent infections • Management of bacterial skin infections has become more challenging because of growing antibiotic resistance • The high prevalence and moderate morbidity of primary bacterial infections warrants their being made a public health priority. Recognising impetigo Impetigo is a contagious, superficial skin lesions caused, for example, by cuts, abra- infection caused primarily by Staphylococcus sions, scabies or herpes simplex sores, are aureus or Streptococcus pyogenes. It does vulnerable to secondary infection.³ This article was made possible not extend beyond the epidermis, and the Impetigo is classically divided into two by an unrestricted educational associated lesions do not form ulcers or types: nonbullous and bullous. grant from Adcock Ingram, which had no control over leave scars when they heal.² Nonbullous impetigo accounts for content. Primary infection can take hold via around 70% of cases, and is more conta- direct invasion of normal unbroken skin, gious than the bullous form.4 It is usually or when the integrity of the skin’s natu- caused by S aureus, but sometimes by S ral defence barrier is breached. Existing pyogenes or by both agents together.² It Adcock Ingram Derm.indd 1 2018/01/29 3:55 PM SEPTEMBER 2019 I 1 Primary bacterial skin infections tends to affect exposed areas such as the exfoliative toxin associated with certain face, hands and feet. The initial lesions strains of S aureus. Bullous impetigo may are small clusters of vesicles or pustules. sometimes also affect the oral mucosa, When these rupture, the discharged pus and in infants extensive lesions may be forms a honey-yellow crust that adheres accompanied by systemic symptoms such to the lesion’s moist, erythematous base. as fever and diarrhoea. Bullous impetigo Mild regional enlargement of the lymph is more likely to cause pain or discomfort nodes may be present. Nonbullous impe- than nonbullous impetigo.4 tigo is generally self-limiting and can be Ecthyma is a form of impetigo in which expected to resolve in around two weeks.4 infection penetrates into the dermis, caus- Bullous impetigo, caused by S aureus ing necrotic shallow ulcers with thick, alone, is considered to be less conta- brown-black crusts that appear ‘punched Impetigo is the most gious than nonbullous impetigo. It most out’ when crusted or purulent matter is common childhood frequently affects the face, hands, feet, removed. It occurs most commonly on skin infection: it is armpits, torso or perianal area. Lesions the lower limbs in debilitated or elderly estimated that over typically are thin-walled, transparent ves- patients.² 162 million children icles that increase rapidly in size to form Patients with impetigo may complain large blisters, or bullae, containing a clear of itchiness and should be advised against in the world have yellow fluid that becomes darker and touching or scratching the lesions as this the condition at any cloudy. When a lesion ruptures it devel- can spread the infection. one time ops a brown, varnish-like crust due to an Ph.wittaya.Shutterstock. https://en.wikipedia.org/wiki/Bullous_impetigo Nonbullous impetigo Bullous imeptigo after rupture of bullae Impetigo prevalence, risk factors and social impact Impetigo is the most common childhood through systemic conditions (e.g. HIV skin infection: it is estimated that over infection, diabetes, obesity or hepatitis), 162 million children in the world have or who are receiving immunosuppressant the condition at any one time − predomi- treatment, are also more vulnerable to nantly in low- and low- to middle-income bacterial infection.¹ countries and in underprivileged commu- Impetigo and folliculitis tend to recur nities within high-income countries. The and persist in patients with HIV dis- EARN FREE peak incidence is seen in children between ease, especially in children. HIV-positive CPD POINTS two and five years old, with a drop-off as patients have increased rates of S aureus age increases. A systematic review of the colonisation, and in cases of advanced Join our CPD community at global epidemiology of impetigo found HIV/AIDS it is not uncommon for this to the median prevalence to be 12.3% in chil- lead to sepsis and deep tissue infection.6 www.denovomedica.com dren and 4.9% in adults.5 Despite the high prevalence of impetigo Risk factors include hot, humid cli- and other primary infections, these often and start to earn today! mates; lower socioeconomic status; poor go under-recognised, especially in the hygiene; household overcrowding; and developing world, and the associated bur- chronic staphylococcal or streptococcal den of disease is frequently under-appre- infection of the upper respiratory tract.5 ciated. In resource-poor communities Patients who are elderly or debilitated impetigo has a significant negative impact 2 I SEPTEMBER 2019 Primary bacterial skin infections on well-being, and represents a high cost dermatological condition with potential to families in terms of treatment expenses lifelong consequences if left untreated. and missed school days. Especially when Given its high prevalence and moderate impetigo occurs as a secondary infec- morbidity, impetigo (as well as the other tion in conjunction with scabies lesions, primary skin infections) deserves more it is considered to be a major childhood attention as a public health priority.5 Treatment of impetigo Diagnosis of impetigo is usually based second-line options. With retapamulin, on patient history and recognition of the irritation at the application site is the characteristic lesions. Only in cases of most common adverse effect. Mupirocin persistent or recurrent impetigo is it nec- contains polyethylene glycol which is essary to have cultures done of the lesions potentially nephrotoxic when absorbed (to identify methicillin-resistant S aureus, from broken skin; caution is therefore or MRSA) and the nose (to identify a advised when using it in patients with causative nasopharyngeal reservoir of S renal impairment.² aureus).4 Systemic antibiotics are appropriate Mild, localised impetigo is typically for more severe or widespread impetigo treated with a topical antibiotic (Table infection, and for ecthyma. First-line oral 1). To increase the medication’s efficacy, antibiotics include flucloxacillin, erythro- before applying it to the affected areas mycin or clarithromycin. Flucloxacillin these may be soaked and carefully washed is a semi-synthetic penicillin that is well with soap and water to remove crusted absorbed; the main potential side-effects material.² are gastrointestinal (nausea, vomit- While MRSA usually Impetigo responds well to fusidic acid, ing and diarrhoea) and dermatological the recommended first-line topical anti- hypersensitivity reactions such as rash. causes mild skin biotic for this infection. Fusidic acid is Erythromycin belongs to the macrolide infections, these applied as a 2% cream 3-4 times daily until class of antibiotics that is unrelated to can become more the lesions resolve, which can be expected penicillins, making it suitable for use severe, and it may in around seven days. It is active against in patients who have penicillin allergy. infect other parts of most Gram-positive bacteria, especially Common side-effects may include nau- Staphylococcus species, and has no sig- sea, vomiting and diarrhoea, and skin the body such as the nificant side-effects; hypersensitivity reac- reactions such as rash and urticaria. lungs, urinary tract tions may occur in rare cases.² Clarithromycin has a similar action to or bloodstream Retapamulin and mupirocin are erythromycin but may be better tolerated.² MRSA as a cause of impetigo and other primary skin infections MRSA, which can be hospital or com- only and their