Impetigo Organism-Specific Therapy

Impetigo  is a contagious, superficial bacterial skin infection commonly seen in children. ^[1]  Unlike in the past, most cases of impetigo are caused by Staphylococcus aureus, with growing frequency of methicillin-resistant isolates. Group A beta-hemolytic streptococci are implicated in 20% to 30% of cases. ^[2] Group C and G beta-hemolytic streptococci rarely may cause impetigo. Microbial invasion generally follows the loss of skin integrity, such as due to skin abrasion, trauma, or an insect bite. The lesions generally are localized and are without systemic toxicity. Two different clinical forms of impetigo have been recognized: nonbullous (70% of cases) and bullous (30% of cases). ^[3]

Nonbullous impetigo — Initial lesions are papules that become vesicular and later pustular. Eventual rupture of pustular lesions results in the apperance of characteristic thick crust with a somewhat golden appearance.  Lesions commonly are localized and most frequently are located on the face and extremities. Streptococci cause nonbullous impetigo. 

Bullous impetigo  — Bullous impetigo is characterized by the appearance of large flaccid bullae at the site of infection. These are filled with fluid that initially is clear but later turns turbid. A thin varnish-like brownish crust is noted following the rupture of bullous lesions. ^[4] Bullous impetigo more frequently is noted on the trunk. It is caused by strains of S aureus that produce exfoliative toxin A causing cleavage in the superficial skin layer. ^[5]

Treatment of impetigo:

Timely therapy of impetigo is necessary to hasten recovery and to prevent nonsuppurative complications such as poststreptococcal glomrulonephritis and rheumatic fever. Impetigo can be treated with topical therapy when limited skin is involved and in the absence of any complications. Oral antibiotic therapy is indicated for patients with more extensive skin lesions, outbreaks of poststreptococcal glomerulonephritis, and when multiple infections have occurred within the home, daycare, or athletic-team settings. ^[6]  

Topical therapy of impetigo:

Topical therapy results in fewer side effects as compared with oral therapy. Mupirocin and retapamulin both are effective topical agents. ^[6]  Ozenoxacin cream offers a potent bactericidal activity against the causative agents of impetigo. It has demonstrated clinical efficacy and safety in patients with impetigo and was approved by the US Food and Drug Administration (FDA) in 2017.9 All of these topical agents are effective against impetigo due to S aureus (including methicillin-resistant strains) and beta-hemolytic streptococci. Localized, uncomplicated impetigo can be treated with one of the topical agents listed in table 1 below. Topical therapy for 5 days is considered adequate.

Table 1. Topical Therapy of Impetigo (Open Table in a new window)

Oral therapy of impetigo:

Widespread and complicated impetigo is treated with an oral antibiotic. Organism-specific oral therapeutic regimens for impetigo are listed below.

 

Therapy of impetigo due to Group A beta-hemolytic streptococci

Impetigo due to beta-hemolytic streptococci can be treated with one of the oral antibiotics listed in table 2 below.  A 7-day course of treatment is considered adequate.

Table 2. Therapy of Impetigo Due to Group A Beta-hemolytic Streptococci (Open Table in a new window)

 

Therapy of impetigo due to methicillin-susceptible S aureus  

Impetigo due to methicillin-susceptible S aureus can be treated with one of the oral antibiotics listed in table 3 below.  A 7-day course of treatment is considered adequate.

Table 3. Therapy of Impetigo Due to Methicillin-susceptible S aureus   (Open Table in a new window)

 

Therapy of impetigo  due to methicillin-resistant S aureus  

Impetigo due to methicillin-resistant S aureus can be treated with one of the oral antibiotics listed in table 4 below. ^[7]  A 7-day course of treatment is considered adequate.

Table 4. Therapy of Impetigo Due to Methicillin-resistant S aureus   (Open Table in a new window)

 

Alternate treatment of impetigo for patients with allergy to beta-lactam antibiotics

Impetigo in patients allergic to beta-lactam antibiotics can be treated with one of the oral antibiotics listed in table 5 below.  A 7-day course of treatment is considered adequate.

Table 5. Alternate Treatment of Impetigo for Patients with Allergy to Beta-lactam Antibiotics (Open Table in a new window)

Unless cultures reveal only beta-hemolytic streptococci, empiric oral therapy of impetigo should be effective for the treatment of both S. aureus and streptococcal infections. Cephalexin and dicloxacillin are appropriate empiric choices unless the presence of methicillin-resistant S. aureus is considered likely.  Oral trimethoprim-sulfamethoxazole may also be an alternative for treating impetigo. It has excellent activity against the community-acquired methicillin-resistant S. aureus and has been shown more recently to be effective in the treatment of skin and soft tissue infections due to group A beta-hemolytic streptococci. ^[8] Impetigo is contagious. Contact precautions should be used in hospitalized patients until 24 hours after the administration of antibiotics to prevent spread of infection. ^[9]