Common Skin Infections

Divya Singh-Behl

Kenneth J. Tomecki

Bacterial infections

Humans are natural hosts for many bacterial species that colonize the skin as normal flora. Staphylococcus aureus and Streptococcus pyogenes are infrequent resident flora, but they account for a wide variety of bacterial pyodermas. Predisposing factors to infection include minor trauma, preexisting skin disease, poor hygiene, and, rarely, impaired host immunity.

Impetigo

Definition and Prevalence

Impetigo is a superficial skin infection usually caused by S. aureus and occasionally by S. pyogenes. Impetigo affects approximately 1% of children.

Pathophysiology

S. aureus produces a number of cellular and extracellular products, including exotoxins and coagulase, that contribute to the pathogenicity of impetigo, especially when coupled with preexisting tissue injury.

Signs, Symptoms, and Diagnosis

Two clinical types of impetigo exist: nonbullous and bullous. The nonbullous type is more common and typically occurs on the face and extremities, initially with vesicles or pustules on reddened skin that eventually rupture to leave the characteristic honey-colored (yellow-brown) crust (Fig. 1). Bullous impetigo, almost exclusively caused by S. aureus, exhibits flaccid bullae with clear yellow fluid that rupture and leave a golden-yellow crust. Diagnosis depends on clinical presentation and confirmation by culture. 1

Treatment

For most patients with impetigo, topical treatment is adequate, either with bacitracin (Polysporin) or mupirocin (Bactroban), applied three times a day for 7 to 10 days. Systemic therapy may be necessary for patients with extensive disease (Table 1). . 2

Table 1: Oral Antistaphylococcal Antibiotics

Drug Adult Dosage Children's Dosage

Cephalexin 250-500 mg qid 25-50 mg/kg/day in 2 doses

Clindamycin 150-300 mg qid 8-16 mg/kg/day in 3-4 doses

Dicloxacillin 125-500 mg qid 12.5 mg/kg/day in 4 doses

Erythromycin 250-500 mg qid 30-50 mg/kg/day in 4 doses

Folliculitis, Furunculosis, and Carbunculosis

Definition and Prevalence

Folliculitis is a superficial infection of the hair follicles characterized by erythematous, follicular-based papules and pustules. Furuncles are deeper infections of the hair follicle characterized by inflammatory nodules with pustular drainage, which can coalesce to form larger draining nodules. The prevalence of folliculitis is unknown.

Pathophysiology

S. aureus is the usual pathogen, although exposure to Pseudomonas aeruginosa in hot tubs or swimming pools can lead to folliculitis.

Signs, Symptoms, and Diagnosis

Folliculitis is generally asymptomatic, but it may be pruritic or even painful. Commonly affected areas are the beard, posterior neck, occipital scalp, and axillae (Fig. 2). Often a continuum of folliculitis, furunculosis (furuncles) arises in hair-bearing areas as tender, erythematous, fluctuant nodules that rupture with purulent discharge (Fig. 3). Carbuncles are larger and deeper inflammatory nodules, often with purulent drainage (Fig. 4), and commonly occur on the nape of the neck, back, or thighs. Carbuncles are often tender and painful and occasionally accompanied by fever and malaise. 1–3

Treatment

Topical treatment with clindamycin 1% or erythromycin 2%, applied two or three times a day to affected areas, coupled with an antibacterial wash or soap, is adequate for most patients with folliculitis. Systemic antistaphylococcal antibiotics (see Table 1) are usually necessary for furuncles and carbuncles, especially when cellulitis or constitutional symptoms are present. 2 Small furuncles can be treated with warm compresses three or four times a day for 15 to 20 minutes, whereas larger furuncles and carbuncles often warrant incision and drainage.

Ecthyma

Definition and Prevalence

Ecthyma is a deep infection of the skin that resembles impetigo. Ecthyma is somewhat common in patients with poor hygiene or malnutrition, or both.

Pathophysiology

S. aureus or S. pyogenes is the usual pathogen of ecthyma.

Signs, Symptoms, and Diagnosis

Infection begins with vesicles and bullae that progress to punched-out ulcerations with an adherent crust, which heals with scarring. The most common site of infection is the legs. Diagnosis depends on clinical presentation with confirmation by culture. 3,4

Treatment

Ecthyma requires treatment with an oral antistaphylococcal antibiotic (see Table 1), coupled with warm compresses three or four times a day for 15 to 20 minutes.2)

Erysipelas and Cellulitis

Definition and Prevalence

Erysipelas is a superficial streptococcal infection of the skin. Cellulitis is a deeper process that extends to the subcutis. Erysipelas has a predilection for young children and the elderly.

Pathophysiology

S. aureus and S. pyogenes are the most common pathogens responsible for erysipelas and cellulitis. S. pyogenes produces enzymes that promote infection with systemic manifestations, such as fever and chills, tachycardia, and hypotension. Predisposing factors for erysipelas include venous stasis or insufficiency, diabetes mellitus, trauma, and alcoholism. 3,4

Signs, Symptoms, and Diagnosis

Classically, erysipelas is a tender, well-defined, erythematous, indurated plaque on the face or legs (Fig. 5). Cellulitis is a warm, tender, erythematous, and edematous plaque with ill-defined borders that expands rapidly. Cellulitis is often accompanied by constitutional symptoms, regional lymphadenopathy, and occasionally bacteremia (Fig. 6). 3,4

Treatment

Penicillin (250 to 500 mg, four times daily for 7-10 days) is the treatment of choice for erysipelas; parenteral therapy may be necessary for extensive or facial disease. An oral antistaphylococcal antibiotic (see Table 1) is the treatment of choice for cellulitis; parenteral therapy is warranted for patients with extensive disease or with systemic symptoms as well as for immunocompromised patients. Good hygiene, warm compresses three or four times a day for 15 to 20 minutes, and elevation of the affected limb help to expedite healing.

Necrotizing Fasciitis

Definition and Prevalence

Necrotizing fasciitis is a rare infection of the subcutaneous tissues and fascia that eventually leads to necrosis.

Pathophysiology

S. pyogenes can be the sole pathogen responsible for necrotizing fasciitis, but most patients have a mixed infection with other aerobes (groups B and C streptococci) and anaerobes (Clostridium spp). Common predisposing factors are injuries to soft tissues, such as abdominal surgery, abrasions, surgical incisions, diabetes, and intravenous drug abuse. 5,6

Signs, Symptoms, and Diagnosis

Infection begins with warm, tender, reddened skin and inflammation that rapidly extends horizontally and vertically. The most common site for infection is the legs, followed by the perineum (Fig. 7). Within 48 to 72 hours, affected skin becomes dusky, and bullae form, followed by necrosis and gangrene, often with crepitus. Without prompt treatment, fever, systemic toxicity, organ failure, and shock can occur, often followed by death. Computed tomography or magnetic resonance imaging can help to delineate the extent of infection. Biopsy for histology, Gram stain, and tissue culture help to identify the causative organism(s). 5,6

Treatment

Necrotizing fasciitis is a surgical emergency requiring prompt surgical débridement, fasciotomy, and, occasionally, amputation of the affected extremity to prevent progression to myonecrosis. Treatment with parenteral antibiotics (usually gentamicin and clindamycin) is mandatory. Even with treatment, mortality approaches 70%.

Fungal and yeast infections

Dermatophytosis

Definition and Prevalence

Dermatophytosis implies infection with fungi, organisms with high affinity for keratinized tissue, such as the skin, nails, and hair. Trichophyton rubrum is the most common dermatophyte worldwide.

Pathophysiology

Three fungal genera—Trichophyton, Microsporum, and Epidermophyton—account for the vast majority of infections. Fungal reservoirs for these organisms include soil, animals, and infected humans.

Signs, Symptoms, and Diagnosis

Tinea pedis (athlete's foot) is the most common fungal infection in humans in North America and Europe. 4 Affected skin is usually pruritic, with scaling plaques on the soles, extending to the lateral aspects of the feet and interdigital spaces (Fig. 8), often with maceration.

Tinea cruris (jock itch) occurs in the groin and on the upper, inner thighs and buttocks as scaling annular plaques (Fig. 9); disease is more common in men and typically spares the scrotum.

Tinea capitis, or fungal infection of the scalp, is most common in children. It is characterized by scaly, erythematous skin, often with hair loss. Tinea capitis can resemble seborrheic dermatitis. Kerion celsi is an inflammatory form of tinea capitis, characterized by boggy nodules, usually with hair loss and regional lymphadenopathy.

Tinea corporis (body), faciei (face), and manuum (hands) represent infections of different sites, each invariably with annular scaly plaques. Tinea unguium (onychomycosis) is fungal nail disease, characterized by thickened yellow nails and subungual debris (Fig. 10).

Potassium hydroxide preparation or culture help to establish the diagnosis for all forms of fungal infections. 2

Treatment

For most patients, topical treatment with terbinafine (Lamisil), clotrimazole (Lotrimin, Mycelex), or econazole (Spectazole) cream is adequate when applied twice daily for 6 to 8 weeks. For onychomycosis, tinea capitis, and extensive dermatophyte disease, systemic treatment is often necessary: itraconazole (Sporanox) or terbinafine (Lamisil) for nail disease, and griseofulvin for scalp or extensive dermatophyte disease. 7–9

Candidiasis

Definition and Prevalence

Cutaneous candidiasis is a yeast infection caused primarily by Candida albicans. Infection is common in immunocompromised patients, diabetics, the elderly, and patients receiving antibiotics.

Pathophysiology

C. albicans commonly resides on skin and mucosal surfaces. Alterations in the host environment can lead to its proliferation and subsequent skin disease.

Signs, Symptoms, and Diagnosis

Candidal intertrigo is a specific infection of the skin folds (axillae, groin), characterized by reddened plaques, often with satellite pustules (Fig. 11). Thrush is oropharyngeal candidiasis, characterized by white nonadherent plaques on the tongue and buccal mucosa. Paronychia is an acute or chronic infection of the nail characterized by tender, edematous, and erythematous nail folds, often with purulent discharge (Fig. 12); this disease is common in diabetics. Angular cheilitis is the presence of fissures and reddened scaly skin at the corner of the mouth, which often occurs in diabetics and in those who drool or chronically lick their lips (Fig. 13).

Candidal vulvovaginitis is an acute inflammation of the perineum characterized by itchy, reddish, scaly skin and mucosa; creamy discharge; and peripheral pustules. The counterpart in men is balanitis, characterized by shiny reddish plaques on the glans penis, which can affect the scrotum. Balanitis occurs almost exclusively in uncircumcised men. 2

Treatment

For candidal intertrigo and balanitis, topical antifungal agents such as clotrimazole, terbinafine, or econazole cream, applied twice daily for 6 to 8 weeks, is usually curative when coupled with aeration and compresses. For thrush, the treatment is nystatin suspension or clotrimazole troches four to six times daily until symptoms resolve. Systemic antifungal drugs, such as fluconazole 100 to 200 mg/day or itraconazole 100 to 200 mg/day, for 5 to 10 days may be necessary for severe or extensive disease. For paronychia, treatment consists of aeration and a topical antifungal agent such as terbinafine, clotrimazole, or clotrimazole for 2 to 3 months; occasionally, oral antistaphylococcal antibiotics (see Table 1) are needed, coupled with incision and drainage for secondary bacterial infection. Cheilitis resolves with aeration, application of a topical antifungal agent, and discontinuation of any aggravating factors. A single 150-mg dose of fluconazole, coupled with aeration, is usually effective for vulvovaginitis. 10

Tinea (Pityriasis) Versicolor

Definition and Prevalence

Tinea versicolor is a common superficial infection of the skin caused by the ubiquitous yeast Pityrosporum ovale. Prevalence is high in hot, humid climates.

Pathophysiology

P. ovale produces phenolic compounds that inhibit tyrosinase, which can produce hypopigmentation in many patients.

Signs, Symptoms, and Diagnosis

Infection produces discrete and confluent, fine scaly, well-demarcated, hypopigmented or hyperpigmented plaques on the chest, back, arms, and neck (Fig. 14). Disease usually occurs in warmer months or in hot, humid climates. Potassium hydroxide preparation exhibits short hyphae and spores with a spaghetti-and-meatballs appearance.

Treatment

Selenium sulfide shampoo (2.5%) or ketoconazole shampoo is the mainstay of treatment, applied to the affected areas and the scalp daily for 3 to 5 days, then once a month thereafter. Alternatively, a variety of topical antifungal agents, including terbinafine, clotrimazole, or econazole cream, applied twice daily for 6 to 8 weeks, constitute adequate treatment, especially for limited disease. 11

Viral infections

Herpes Simplex

Definition and Prevalence

Herpes simplex virus (HSV) infection is a painful, self-limited, often recurrent dermatitis, characterized by small grouped vesicles on an erythematous base. Eighty-five percent of the population has antibody evidence of HSV type 1 infection. HSV type 2 infection is responsible for 20% to 50% of genital ulcerations.

Pathophysiology

Disease follows implantation of the virus via direct contact at mucosal surfaces or on sites of abraded skin. After primary infection, the virus travels to the adjacent dorsal ganglia, where it remains dormant unless reactivated by psychological or physical stress, menses, or sunlight.

Signs, Symptoms, and Diagnosis

Primary infection occurs most often in children, exhibiting vesicles and erosions on reddened buccal mucosa, the palate, tongue or lips (acute herpetic gingivostomatitis) (Fig. 15). Herpes labialis, (fever blisters or cold sores) appears as grouped vesicles on red denuded skin, usually the vermilion border of the lip; infection represents reactivated HSV. Primary genital infection is an erosive dermatitis on the external genitalia that occurs about 7 to 10 days after exposure; intact vesicles are rare. Recurrent genital disease is common (approximately 40% of affected patients). Viral culture helps to confirm the diagnosis; direct fluorescent antibody (DFA) is a helpful but less specific test. Serology is helpful only for primary infection.

Treatment

Acyclovir remains the treatment of choice for HSV infection; newer antivirals, such as famciclovir and valacyclovir, are also effective (Table 2). For recurrent infection (more than six episodes per year), suppressive treatment (see Table 2) is warranted. Primary infection in immunosuppressed patients requires treatment with acyclovir 10 mg/kg every 8 hours for 7 days.

Table 2: Oral Antivirals

Indication Acyclovir Famciclovir Valacyclovir

Primary HSV 200 mg 5x/day or 400 mg tid x 10 days 500 mg bid or 250 mg tid x 7 days 1 g bid x 10 days

Recurrent HSV 400 mg tid x 5 days 125 mg bid x 5 days 500 mg bid x 5 days

Suppression 400 mg bid 250 mg bid 1 g or 500 mg qd

Herpes zoster 800 mg 5x/day x 7-10 days 500 mg tid x 7 days 1 g tid x 7 days

HSV, herpes simplex virus.

Herpes Zoster

Definition and Prevalence

Herpes zoster (shingles) is an acute, painful dermatomal dermatitis that affects approximately 10% to 20% of adults, often in the presence of immunosuppression.

Pathophysiology

Zoster represents reactivation of latent varicella zoster virus within a single dermatome.

Signs, Symptoms, and Diagnosis

Herpes zoster is primarily a disease of adults. It typically begins with pain in a dermatomal or bandlike pattern followed by grouped vesicles within the dermatome (Fig. 16), and occasionally accompanied by fever and malaise. Most patients with zoster do well with only symptomatic treatment, but post-herpetic neuralgia (continued dysthesias and pain after resolution of skin disease) is common in the elderly. Disseminated zoster is uncommon and occurs primarily in immunocompromised patients. Diagnostic tests are the same as for HSV. 2

Treatment

Zoster deserves treatment, if possible, with rest, analgesics, compresses applied to affected areas, and antiviral therapy, if possible, within 24 to 72 hours of disease onset (see Table 2). Disseminated and ophthalmic zoster warrants treatment with acyclovir 10 mg/kg intravenously every 8 hours for 7 days.

Warts

Definition and Prevalence

Warts are common and benign epithelial growths caused by human papillomavirus (HPV). Warts affect approximately 5% of the population.

Pathophysiology

HPV infection follows inoculation of the virus into the epidermis through direct contact, usually facilitated by a break in the skin.

Signs, Symptoms, and Diagnosis

The common wart is the most common type: a, hyperkeratotic, flesh-colored papule or plaque studded with small black dots (thrombosed capillaries) (Fig. 17). Other types of warts include flat warts (verruca plana), plantar warts, and condyloma acuminatum (venereal warts). Clinical appearance and location usually suggest the diagnosis.

Treatment

Therapy is variable and often challenging. Most modalities are destructive: cryosurgery, electrodesiccation, curettage, and application of various topical products such as trichloroacetic acid, salicylic acid, podophyllin, and canthacur. For stubborn warts, laser therapy is often necessary. The immunomodulator, imiquimod cream (Aldara), is a novel topical agent recently approved for the treatment of condyloma acuminatum. Sexual partners of patients with condyloma warrant examination, and women require gynecologic examination.

Molluscum Contagiosum

Definition and Prevalence

Molluscum contagiosum is an infectious viral disease caused by the poxvirus. Infection is common in children, sexually active adults, and patients with human immunodeficiency virus (HIV) infection.

Pathophysiology

The disease follows direct contact with the virus, which replicates in the cytoplasm of cells and induces hyperplasia.

Signs, Symptoms, and Diagnosis

Molluscum are smooth flesh-colored, dome-shaped, umbilicated papules with a central keratotic plug (Fig. 18). They usually resolve spontaneously, but they often persist in immunocompromised patients.

Treatment

Treatment might not be necessary. If indicated, treatment is similar to the modalities outlined for warts.

Summary

Impetigo is a superficial skin infection usually caused by Staphylococcus aureus and occasionally by Streptococcus pyogenes.

Folliculitis is a superficial infection of the hair follicles characterized by erythematous, follicular-based papules and pustules.

Ecthyma is a deep infection of the skin that resembles impetigo. Ecthyma is somewhat common in patients with poor hygiene or malnutrition.

Erysipelas is a superficial streptococcal infection of the skin.

Necrotizing fasciitis is a rare infection of the subcutaneous tissues and fascia that eventually leads to necrosis.

Dermatophytosis implies infection with fungi, organisms with high affinity for keratinized tissue, such as the skin, nails, and hair. Trichophyton rubrum is the most common dermatophyte worldwide.

Cutaneous candidiasis is a yeast infection caused primarily by Candida albicans.

Tinea versicolor is a common superficial infection of the skin caused by the ubiquitous yeast Pityrosporum ovale.

Herpes simplex virus infection is a painful, self-limited, often recurrent dermatitis, characterized by small grouped vesicles on an erythematous base.

Warts are common and benign epithelial growths caused by human papillomavirus.

Herpes zoster (shingles) is an acute, painful dermatomal dermatitis that affects approximately 10% to 20% of adults, often in the presence of immunosuppression.

Molluscum contagiosum is an infectious viral disease caused by the poxvirus.