Dr P. Marazzi/Science Source
The patient is empirically diagnosed with AD complicated by bacterial infection. A skin swab culture is positive for Staphylococcus aureus and Streptococcus pyogenes.
AD is a common chronic inflammatory skin disease characterized by pruritus, eczematous lesions, xerosis, and lichenification. Individuals of all ages may be affected by AD, although it normally begins in infancy. Studies suggest that as many as 17.1% of adults and 22.6% of children are affected by AD. The disease is associated with diminished quality of life, sleep disturbance, depression, and anxiety. To further complicate matters, patients with AD have a significantly increased risk for recurrent skin infections, including bacterial, viral, and fungal infections.
The underlying mechanisms of bacterial infection in AD are multifactorial and involve both host and bacterial factors. Factors implicated in the increased risk for infection in patients with AD include skin barrier defects, suppression of cutaneous innate immunity by type 2 inflammation, S aureus colonization, and cutaneous dysbiosis. Up to 90% of patients with AD are colonized with S aureus. It has been theorized that the host skin microbiota may play a role in protecting against S aureus colonization and infection in patients with AD. Additionally, bacterial virulence factors, such as the superantigens, proteases, and cytolytic phenol‐soluble modulins secreted by S aureus, trigger skin inflammation and may also contribute to bacterial persistence and/or epithelial penetration and infection.
Overt bacterial infection in patients with AD can be recognized by the presence of weeping lesions, honey‐colored crusts, and pustules. However, cutaneous erythema and warmth, oozing associated with edema, and regional lymphadenopathy are seen in both AD exacerbations and in patients with infection, making clinical diagnosis challenging. In addition, anatomical site‐ and skin type-specific features may disguise signs of infection, and the high frequency of S aureus colonization in AD makes positive skin swab culture of suspected infection an unreliable diagnostic tool.
S pyogenes is the second most common cause of skin and soft tissue infections in AD (S aureus is the leading cause, although data suggest that pediatric patients are not likely to be affected by superinfections caused by methicillin-resistant S aureus [MRSA]). S pyogenes may cause infections in patients with AD alone or in combination with S aureus. Patients with these skin infections usually present with pustules or impetigo. The lesions may appear as punched-out erosions with scalloped borders that mimic eczema herpeticum or eczema coxsackium. According to guidelines from the American Academy of Dermatology, the presence of purulent exudate and pustules on skin examination may suggest a diagnosis of secondary bacterial infection over inflammation from dermatitis.
The use of systemic antibiotics in the treatment of noninfected AD is not recommended; however, systemic antibiotics can be recommended for patients with clinical evidence of bacterial infection, in addition to standard treatment for AD, including the concurrent application of topical steroids. For patients with AD who have signs and symptoms of systemic illness, hospitalization and empirical intravenous antibiotics are recommended. The antibiotic regimen should provide coverage against S aureus because this is the most frequently identified bacterial pathogen in AD.
When treating critically ill patients, treatment that provides coverage for both MRSA and methicillin-susceptible S aureus (MSSA) with vancomycin and an antistaphylococcal beta-lactam is appropriate. In patients with severe but non–life-threatening infections, vancomycin may be used alone as empirical therapy, pending culture results. Clindamycin can also be considered, particularly if there is no concern for an endovascular infection and the local incidence of clindamycin resistance is less than 15%.
Bacteremia triggered by S aureus initially requires the use of a bactericidal intravenous agent. For MRSA, vancomycin is the first-line agent. Cefazolin and nafcillin are both acceptable first-line agents for MSSA, although nafcillin can cause venous irritation and phlebitis when administered peripherally. Among children with S aureus bacteremia, an oral agent to which the isolate is susceptible is appropriate, as long as there are no concerns for ongoing bacteremia or endovascular complications. Duration of therapy should be determined by the clinical response; 7-14 days is usually recommended.
For patients with AD with uncomplicated, nonpurulent skin infection, a beta-lactam antibiotic that covers both S aureus and beta-hemolytic streptococci (eg, cefazolin or cephalexin) may be appropriate pending clinical response or culture and considering local epidemiology and resistance patterns. In patients who present with a skin abscess, history of MRSA colonization, close contacts with a history of skin infections, or recent hospitalization, consideration of coverage for MRSA is recommended. Acceptable oral options for MRSA skin infections in both children and adults include clindamycin, doxycycline, trimethoprim-sulfamethoxazole, and linezolid, assuming that the isolate is susceptible in vitro. Finally, topical mupirocin ointment for 5-10 days is an appropriate treatment for patients with AD with minor, localized skin infections such as impetigo.
William D. James, MD, Professor, Department of Dermatology, University of Pennsylvania, Philadelphia
Disclosure: William D. James, MD, has disclosed the following relevant financial relationships:
Received income in an amount equal to or greater than $250 from: Elsevier