What Is Impetigo?

Impetigo is a bacterial infection that affects the superficial layer of the skin.¹ Though the infection is generally mild and can resolve spontaneously, it is also highly contagious so antibiotics are often prescribed to hasten recovery.^{2, 3, 4} Transmission is by skin-to-skin contact.^{6, 13}

Impetigo can affect all ages but is commoner in children between 2-5 years.^{4, 6, 13} Risk factors include diseases or treatment that suppress the immune system (such as HIV, diabetes and chemotherapy), hot humid climate (summer in temperate regions like the UK), crowded environment (such as schools, hostels, military barracks), skin trauma (from bites, abrasions, burns, lacerations. The nostrils and area around the mouth are the parts of the body most at risk of trauma) and poor hygiene (such as sharing clothes and towels).^{5, 6, 8,13}

Due to paucity of literature studies, the true number of people living with impetigo is not known.¹⁹ However, it is estimated that there are over 140 million people at each time point, with children accounting for over 100 million.^13,14 In the UK, the annual incidence is estimated to be 2.8% in children aged 0-4 years, and 1.6% in children aged 5–15 years.^{5, 13}

Overview

Impetigo is a mild but highly contagious infection of the epidermis (superficial layer of the skin). It occurs in all ages, though it is most frequent  in children between 2-5 years of age. Risk factors include a weak immune system (either from disease or treatment), humid climate, crowded environment (such as schools, hostels, and military barracks), skin trauma (from bites, abrasions, burns, lacerations), and poor hygiene (such as sharing clothes and towels).

There are three types of impetigo namely nonbullous impetigo, bullous impetigo and ecthyma. Impetigo commonly affects the head and neck (65.4%), upper limbs (19.6%), and lower limbs (7.5% each). The diagnosis is usually based on clinical manifestation, history taking, and physical examination. The classic presentation of Impetigo is golden (honey-colored) crusted lesions. Impetigo usually resolves spontaneously within 2-3 weeks; however, antibiotic treatments are used to reduce the duration (10 days) and spread.

There are other skin conditions that show a similar presentation to impetigo and be inappropriately treated. These may be due to infectious causes from bacteria (such as cellulitis, ecthyma, erysipelas, staphylococcal scalded skin syndrome, and necrotizing fasciitis), fungi (such as candidiasis, tinea corporis, and tinea capitis), parasites (such as scabies), and viruses (such as varicella-zoster and herpes simplex). Or non-infectious causes from contact dermatitis, eczema, insect bites and stings, burns and scalds, drug reactions, and erythema multiforme.⁵ Complications include cellulitis, septicaemia, scarlet fever, scarring, staphylococcal scalded skin syndrome and post-streptococcal glomerulonephritis, but these are a rare occurrence.

Causes 

The skin microbiota refers to the ecosystem of  microorganisms that reside on the skin and provide healthy benefits.¹⁶ However, there are also harmful organisms that also reside on the skin. When there is a break in the integrity of the skin, these organisms penetrate and begin to multiply. In the case of impetigo, the harmful organisms are the bacteria that penetrate the epidermis (outer layer of the skin) and then proliferate.⁴ Impetigo is limited to only the epidermis. In contrast, erysipelas is restricted to the upper dermis while cellulitis involves the deeper dermis and subcutaneous fat.¹³

Impetigo is caused by Staphylococcus aureus or Streptococcus pyogenes (group A streptococci) or a mixture of both.^4,8 It can also be caused by Group C and G streptococci.⁸ The incubation period following infection (time from when an individual is exposed to a causative agent until the first symptoms develop) is 4-10 days. 

Signs and symptoms of Impetigo

There are three types of impetigo namely nonbullous impetigo (also known as impetigo contagiosa), bullous impetigo and ecthyma.¹⁸

Nonbullous impetigo is the most common form, accounting for approximately 70% of cases.⁵ It begins as painless, itchy papules (red sores usually around the nose and lips though they can appear on the limbs and other parts of the face) which break down to form thick, golden crusty lesions (referred to as honey-colored).^4,6 Sometimes, the sores may progress to pustules (pus filled blisters) that rupture to form the golden crusts. When these crusts dry, they leave a red mark that usually fades without scarring.⁴ Systemic symptoms are usually absent, though lymphadenopathy (swelling of the lymph nodes) may be present.¹

Bullous impetigo begins as itchy painful bullae (fluid-filled blisters, usually on the limbs or central core between the waist and neck) which quickly spread, then burst after several days, leaving a yellow crust that also usually fades without scarring.⁴ Bullous impetigo is more likely to occur with non-specific symptoms such as fever, malaise (sick feeling), and swollen lymph nodes.^1,7

In ecthyma, the ulcerative lesions penetrate through the epidermis and deep into the dermis.¹  The lesions may be purulent (containing pus) while the crusts can be honey-coloured or brown-black. 

Though impetigo may be itchy or painful, it is important not to touch or scratch the sores as this can lead to further spread of the infection to other parts of the body or to other people.⁴

Management and treatment for impetigo

Impetigo is usually a mild, self-limiting condition in which the lesions would crust within 2–3 weeks.² However, treatment may be prescribed to reduce the healing time (to within 10 days), spread, and complications.^1,4 Topical antibiotics (antibiotic creams) are used for localized impetigo while oral therapy (antibiotic tablets) are used for widespread impetigo.^{2, 4} 

In localized impetigo, the crust should be removed with soap and warm water before applying a topical antibiotic such as mupirocin, retapamulin, or fusidic acid.^1,4 If impetigo is extensive or if topical antibiotics do not work, oral antibiotics such as flucloxacillin and cephalexin can beused. If MRSA (antibotic resistant bacterial strain) is confirmed, then the recommended treatment is with clindamycin or doxycycline.^1,7,19

Most people remain contagious until after 48 hours of treatment or until the sores have dried and healed, so it is recommended to isolate them from work, school, or any other public gathering until this point.⁴ Complications can occur though they are rare. They include cellulitis, septicemia, scarlet fever, scarring, staphylococcal scalded skin syndrome, and post-streptococcal glomerulonephritis.^6,13

FAQs

How is impetigo diagnosed?

Impetigo is diagnosed based on the clinical presentation , history taking, and physical examination.^1,6 However, laboratory investigations are used if the impetigo lesions persist despite treatment, if the lesions recur or are widespread, or if your GP suspects methicillin-resistant Staphylococcus aureus (MRSA) infection. In this case, skin swabs (from the lesion or blister usually from the nostrils or mouth area will be cultured.⁵ A skin biopsy may also be considered if the lesions are persistent or if bullous impetigo is suspected.¹ 

How can I prevent impetigo?

Prevention of impetigo should prioritize a healthy immune system and environmental health interventions. These include good hand hygiene including washing hands before and after applying creams, avoiding sharing towels or face cloths, resisting the urge to scratch affected areas that are itchy, daily changing beddings and clothing and self-isolation if infected until lesions have crusted over, or until at least 48 hours of treatment. 

Who is at risk of impetigo?

All ages can develop impetigo but children between 2-5 years are most at risk. Other persons at risk are those with a weak immune system (either from disease or treatment), persons living in areas of high humidity, persons living in crowded environments (such as schools, hostels, military barracks), skin trauma from bites, abrasions, burns, lacerations, and poor hygiene (such as sharing clothes and towels). 

How common is impetigo?

Studies on impetigo are limited but it is estimated that there are over 140 million children who have experienced impetigo worldwide. In the UK, the annual incidence in children 0-4 years is 2.8%, while in children 5–15 years, it is 1.6%. 

Is impetigo contagious?

Impetigo is a mild but highly contagious infection that spreads primarily through direct contact and causes sores and blisters. There are other skin conditions that may show a similar presentation to impetigo. These may be due to infectious causes from bacteria (such as cellulitis, ecthyma, erysipelas, staphylococcal scalded skin syndrome, and necrotizing fasciitis), fungi (such as candidiasis, tinea corporis, and tinea capitis), parasites (such as scabies), and viruses (such as varicella-zoster and herpes simplex). Or non-infectious causes from contact dermatitis, eczema, insect bites and stings, burns and scalds, drug reactions, and erythema multiforme.

How long does impetigo last?

Untreated impetigo spontaneously resolves within 2-3 weeks while treated impetigo heals within 10 days. While on treatment, there may be a positive response within 72 hours, however, it is recommended to complete the full course as prescribed.

When should I see a doctor?

Impetigo will usually spontaneously heal, without leaving any serious complications. In the UK, it is recommended to visit your GP if the infection is severe, widespread, or recurring, or if treatment does not work. Depending on the clinical presentation, your GP may prescribe an antiseptic nasal cream, take a swab of the affected skin for testing or refer to a dermatologist (skin specialist) for further tests.⁴

Summary

Impetigo is a mild but highly infectious infection of the epidermis (superficial layer of the skin). It occurs in all ages, though most frequent in children between 2-5 years of age. There are three types of impetigo namely nonbullous impetigo, bullous impetigo, and ecthyma. The diagnosis is usually based on clinical manifestation. The classic presentation is golden (honey-colored) crusted legions. Impetigo usually resolves spontaneously without scarring within 2-3 weeks; however, antibiotic treatment can shorten this time to 10 days. Complications are rare.