Impetigo is a superficial bacter skin infection that is very contagious. Impetigo can be brought about by Streptococcus pyogenes and also Staphylococcus aureus. This page focuses on infections caused by S. Pyogenes, which are also called team A Streptococcus or team A strep.

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Impetigo deserve to be bullous or non-bullous. Toxin-producing S. Aureus reason bullous impetigo. S. Aureus, S. Pyogenes, or both cause non-bullous impetigo, i beg your pardon is likewise called “impetigo contagiosa.”

S. Pyogenes room gram-positive cocci that flourish in chains (see number 1). They exhibit β-hemolysis (complete hemolysis) as soon as grown top top blood agar plates. Lock belong to team A in the Lancefield classification system for β-hemolytic Streptococcus, and thus are likewise called group A streptococci.


Figure 1. Streptococcus pyogenes (group A Streptococcus) ~ above Gram stain. Source: Public health and wellness Image Library,

Clinical Features

Streptococcal impetigo, or non-bullous impetigo, begins as papules. The papules evolve to pustules and also then malfunction to kind thick, adherent crusty lesions (Figure 2). The crusts room typically gold or “honey-colored.” this lesions usually appear on exposed areas of the body, most frequently the face and also extremities. Lot of lesions typically develop. In instances of non-bullous impetigo, physics examination cannot differentiate streptococcal native staphylococcal infection.1


Streptococcal impetigo is most typically spread through direct call with other world with impetigo. People with impetigo are much much more likely to transmit the bacteria 보다 asymptomatic carriers. Crowding, such as found in schools and daycare centers, rises the threat of an illness spread from human being to person.

Lesions deserve to be spread (by fingers and also clothing) to other parts that the body.

Humans space the main reservoir for group A strep. There is no proof to indicate that pets deserve to transmit the bacteria to humans.


Figure 2. Streptococcus pyogenes caused the lesions top top this patient’s left forearm. Source: Public wellness Image Library,

Incubation Period

The incubation duration of impetigo, from emigration of the skin to breakthrough of the properties lesions, is around 10 days.1 that is vital to note not everyone that becomes colonized will go on to develop impetigo.

Risk Factors

Impetigo can happen in human being of every ages, but it is most common among children 2 with 5 years of age. Scabies epidemic and tasks that result in cutaneous cut or abrasions (e.g., sports such as wrestling and also football) boost the danger of impetigo. That is also much more common in tropical or subtropical locations and also in the summer in pleasant climates however can take place anywhere.1

Diagnosis and also Testing

Impetigo is normally diagnosed by physics examination, however physical examination cannot reliably differentiate in between streptococcal and staphylococcal non-bullous impetigo.1 Gram stain or society of the exudate or pus native an impetigo lesion can identify the bacterial cause. However, laboratory experimentation is not essential nor frequently performed in clinical practice.


Antibiotic treatment, whether oral or topical, need to be aimed in ~ both bacteria the are connected with impetigo: group A strep and S. Aureus. Object antibiotics, mupirocin or retapamulin, might be offered when there are just a couple of lesions, while oral antibiotics are provided for multiple lesions.1,2,3

Prognosis and Complications

Rarely, complications can take place after impetigo. Post-streptococcal glomerulonephritis (PSGN) can occur as a delayed non-suppurative complication of impetigo. The most frequently occurs one to 2 weeks ~ the original infection resolves. PSGN is believed to it is in the result of an immune an answer that is motivated by the group A strep infection.


The spread of impetigo deserve to be prevent by extending lesions, treating with antibiotics, and practicing great hand hygiene. Clothing, linens, and towels provided by one infected human should be washed every day and also not common with rather in the household. Persons through impetigo have the right to return to school or job-related after initiating antibiotic treatment if lesions on exposed skin are covered.

The spread out of all types of group A strep infection can be lessened by good hand hygiene, especially after coughing and sneezing and also before preparing foods items or eating, and also respiratory etiquette (e.g., spanning your cough or sneeze).


In the joined States, impetigo is much more common in the summer.1 The world Health Organization estimates that 111 million children in the arising world have streptococcal impetigo at any type of one time.4 higher rates that impetigo are found in crowded and impoverished settings, in warm and humid conditions, and among populations with poor hygiene.

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Bryant AE, Stevens DL. Streptococcus pyogenes. In Bennett J, Dolin R, Blaser M, editors. 8th Mandell, Douglas, and Bennett’s Principles and also Practice of infectious Diseases. Philadelphia (PA): Elsevier; 2015:2:2285–300.