Secondarily Infected Dermatoses
Secondarily infected dermatoses develop when a bacterium invades compromised skin, such as in atopic dermatitis, psoriasis, and allergic contact dermatitis. The bacteria frequently causing secondarily infected dermatoses are Staphylococcus aureus or Streptococcus pyogenes. The following are types of skin infections that may become secondarily infected:
Atopic dermatitis | Allergic contact dermatitis | Psoriasis
Atopic Dermatitis
Atopic dermatitis (AD) is an allergic, chronic inflammatory skin disease. It is characterized by pruritic, erythematous patches with papules and scaling. In children, it is usually found on the face, scalp, extremities and trunk. In adults, it is usually found on the neck, face, wrists and forearms. People with asthma and allergic rhinitis may be predisposed to developing AD. Because of compromised skin surface, AD sufferers frequently develop recurrent bacterial skin infections. These infections can also worsen the disease. S aureus is frequently responsible for secondary infections because people with the disease are commonly colonized with the bacteria. Dermatitis with pustules usually indicates a secondary infection with S aureus.
Secondarily infected AD is treated both with topical and systemic antibiotics; although without signs of infection, oral antibiotics are not thought to be helpful in treating atopic dermatitis. Topical antibiotics are considered effective in patients with infected AD, although some topical antibiotics, such as mupirocin, may lead to resistance.
Allergic Contact Dermatitis
Allergic contact dermatitis is a hypersensitivity skin reaction to a substance and is characterized by a pruritic, papular erythematous rash. The most common allergen causing this reaction is urushiol, the plant oleoresin found in poison ivy, poison oak and poison sumac. Other common agents that trigger allergic contact dermatitis are nickel (found in jewelry), formaldehyde (found in clothing and nail polish), fragrances, preservatives (found in medications and cosmetics), rubber, and chemicals in leather and synthetic shoes. Topical medications, such as hydrocortisone, neomycin, bacitracin, benzocaine and thimerosal may also cause allergic contact dermatitis. Iatrogenic allergic contact dermatitis may occur when these medications are used to treat another form of dermatitis.
When the allergen is removed, allergic contact dermatitis usually resolves in 2 to 4 weeks. It may also be treated with topical corticosteroids or, in more severe cases with extensive oozing, wet-to-dry compresses are employed. Water or aluminum acetate dry the skin, which then allows for the application of topical steroids. When a secondary infection occurs, as in the case of allergic contact dermatitis, the antibiotic treatment algorithm of any secondary infection is recommended.
Psoriasis
Psoriasis is a chronic, life-long skin disease most commonly causing erythematous papules and silver scale plaques. Psoriasis develops as a response triggered by T-lymphocytes in the skin. Hyperproliferation, abnormal differentiation of the epidermis, vascular changes and inflammatory cell infiltrates cause erythema and scaling. There are several different types of psoriasis, which have different clinical features:
- Plaque psoriasis usually affects young adults and features symmetrically distributed plaques on elbows, knees and back. These thick, silvery scales range from 1 to 10 cm in diameter and may be pruritic
- Guttate psoriasis, which occurs mostly in children and young adults as acute eruptions, features multiple lesions, less than 1 cm, usually on the trunk of the body
- Pustular psoriasis is the most severe form, characterized by erythema, scaling and sheets of pustules. Pustular psoriasis can be life-threatening and is associated with fever, diarrhea, malaise, leukocytosis and hypocalcemia
- Inverse psoriasis usually presents without scaling, affecting the inguinal, perineal, genital, intergluteal, axillary and inframammary regions
- Nail psoriasis is characterized by pitting and abnormal nail plate growth, tan-brown nail discoloration and thick crumbling nails
Patients who smoke and abuse alcohol have a higher prevalence of psoriasis; psoriatic patients who abuse alcohol have a higher risk of death. Depending on the severity and type, psoriasis is treated with topical corticosteroids, tar ( in shampoos, creams and oils), calcipotriene, tazarotene, topical calcineurin inhibitors, ultraviolet light, methotrexate, retinoids, immunosuppressive drugs, and immunomodulatory drugs, such as etanercept, alefacept, efalizumab and infliximab.
Typically mild, the disease may be worsened by viral and bacterial infection, such as infection with Streptococcus pyogenes. Similar to any dermatose, when a secondary infection occurs in the case of psoriaris, antibiotics are given.
