[Bacterial Infections] [Viral Infections] [Fungal Infections]


Bacterial infections

Bacterial infections of the skin can be divided by the portion of skin involved. Most bacterial skin infections are caused by Group A Beta-hemolytic Streptococcus (GABHS) and/or Staphylococcal aureus regardless of the depth of the infection. The characteristics, location, and depth of the lesion may suggest one of these two organisms or the other as the more likely causative agent, but together they account for almost all of the bacterial skin infections we see. Less common organisms may be seen in patients who are immunosuppressed, have HIV or diabetes, or have a hospital-acquired infection.

Site Infection Treatment
Epidermis Impetigo
Ecthyma (impetigo with ulceration)
Bullous Impetigo		 Oral Antibiotic*
(topical mupirocin may be used for small areas of mild infection)
Dermis Erysipelas
Cellulitis (involves both dermis and subcutaneous tissue)		 Oral Antibiotic*
IV antibiotics may be indicated based on severity
Dermal Appendages
(hair follicle, nail fold)		 Folliculitis
Carbuncle/Furuncle
Paronychia
Abscess		 Topical or Oral Antibiotic*
Incision and Drainage (I&D) is usually indicated in the treatment of carbuncles, furuncles, and abscess.
Subcutaneous Necrotizing Fasciitis
Cellulitis (see above)		 Hospitalization
IV Antibiotics
Debridement
* Oral antibiotics must cover Group A Beta-hemolytic Streptococci and Staphylococcus aureus. 1st line - dicloxacillin, cephalexin; 2nd line - erythromycin for severe penicillin allergy

Viral infections

Warts

Warts are caused by over 60 subtypes of human papilloma virus (HPV). Warts most commonly occur on the hands, feet, and genitals. The appearance of the wart is strongly related to its location. Warts on the hands (verruca vulgaris) are usually raised and hyperkeratotic. Warts on the soles of the feet (plantar warts) are flat, disrupt skin lines, and have dark dots visible in them. Flat warts (verruca plana) are flat and are usually seen in groups. Finally, genital warts (condyloma acuminata) often have a cauliflower appearance and are transmitted sexually.

Some warts will be symptomatic and regress spontaneously, while others may be painful. The HPV that causes condyloma acuminata has been associated with cervical intraepithelial neoplasia and cervical cancer. Plantar warts and periungual warts are typically associated with the most pain.

Although there are many treatments for warts, some warts do not respond to treatment or recur within a short period of time. Treatment options for warts are found below. For an evidence-based table that estimates efficacy of these various treatment modalities please click here.

Treatment Verrucae Vulgaris Plantar Warts Flat Warts Condyloma Acuminata
Podophyllum Resin X
Podofilox (Condylox) X
Trichloroacetic acid X
Salicylic acid X X X
Topical tretinoin (Retin-A) X
Topical fluorouracil X
Cantharidin X
DNCB X
Cryosurgery X X X X
Hyfrecator X X X
LEEP X X X
Laser X X X
Excision X X X
Injection
Bleomycin injection X X
Interferon injection X



Herpes Viruses

Herpes simplex virus (HSV) types I and II produce vesicular eruptions on the skin with surrounding erythema. The lesions progress to crusts of ulcers before they re-epithelialize. However, the primary episode of HSV I can infect the entire mouth (gingivostomatitis) or be asymptomatic. Recurrent episodes of HSV I often occur on the lips and are commonly called cold sores or fever blisters (not canker sores). HSV II is a sexually transmitted disease that can occur on the genitals, anus, buttocks, or in the mouth. HSV I can occur on the genitals but this is less commonly found in the location compared with HSV II. The varicella-zoster virus initially produces chicken-pox and can be re-activated later and cause zoster (shingles). In Figure 33.3 you can see the dermatomal distribution.

Most infections with HSV and VZV (varicella-zoster virus) are acutely painful, uncomplicated, and resolve spontaneously in one to two weeks. However, there are many complications that can occur with these viruses, especially in infants or immunosuppressed individuals. Once a person is infected with one of these viruses, the virus remains latent in the dorsal root ganglia and can be reactivated. Because we do not have any curative antiviral agents for HSV or VZV the goals of therapy are to diminish pain, viral shedding, duration of symptoms and to prevent recurrences. Although it is common for an individual to have repeated recurrent episodes of HSV, it is rare for zoster to recur. One additional reason for treating zoster with an antiviral agent in older individuals is to prevent post-herpetic neuralgia.

Acyclovir (Zovirax) was the first antiviral agent with proven efficacy against HSV and VZV. Two newer agents now available are Famciclovir (Famvir) and Valacyclovir (Valtrex). All three agents can be used to treat primary and recurrent herpes simplex, herpes zoster and to prevent recurrent herpes simplex. Acyclovir is also FDA-approved to treat acute varicella (chicken-pox). Preliminary data on both newer agents indicates that they are at least as effective for treatment of zoster and herpes simplex as Acyclovir. Both newer agents have the advantage of requiring fewer doses per day and currently Valacyclovir is priced less expensively than Acyclovir and Famciclovir. It remains to be seen if any one of these agents will be shown to be more effective than the others for any of the possible indications described above. While we have newer agents for treatment, we should not forget that we now have the varicella vaccine for primary prevention.

Other viruses

There are other viruses that cause primary skin lesions (molluscum contagiosum) and viruses that produce skin manifestations during a systemic infection (measles, rubella). Detailed information can be found about these viral infections in many dermatology or infectious disease books.

Fungal infections

Fungal infections of the skin occur at many sites and are most often caused by dermatophytes, Candida, or Pityrosporum species. The dermatophytes cause tinea infections which are commonly called "ringworm". Although the Latin word "tinea" means worm, there is no worm in ringworm. Tinea versicolor is misnamed because it is caused by an inflammatory reaction to Pityrosporum species rather than a dermatophyte. Candida can cause cutaneous infections in most intertriginous areas as well as mucosal surfaces. Fungal infections of the nails are most often caused by dermatophytes but can be caused by yeasts and molds.

The typical dermatophyte infection of the body has an annular appearance with central clearing, and redness and scale on the perimeter of this well-demarcated lesion. Dermatophytes can not thrive on mucosal surfaces like Candida can. Candida causes thrush, balanitis, and vaginitis but can also be seen in the groin and under the breast.

The first two columns in the table below summarize the names of the dermatophyte infections and their locations. Tinea in each location has a different appearance and has different diagnostic and treatment issues. A skin scraping treated with KOH and analyzed with a microscope can be helpful when classic hyphae or yeast forms are found on the slide. A negative KOH wet mount does not rule out a fungal infection because false negatives are common when specimen collection is inadequate, when the patient has started OTC antifungals, or when the slide is read by an inexperienced viewer. Fungal cultures can be expensive and take a long time to grow, but may provide the most definitive evidence of fungal infection while providing you with the identity of the fungus.

Dermatophyte Infection Location Treatment Modality Duration
Tinea capitus scalp systemic antifungals 4 - 8 weeks
Tinea corporis body topical antifungals (small area) / systemic antifungals (large area) 2 weeks / 2 - 4 weeks
Tinea cruris groin topical antifungals (small area) / systemic antifungals (large area) 2 weeks / 2 - 4 weeks
Tinea pedis feet topical antifungals (small area) / systemic antifungals (large area) 2 weeks / 2 - 4 weeks
Onychomycosis nails of feet / hands systemic antifungals 3 - 4 months
Tinea capitus causes patchy alopecia with broken hairs and some scaling. Because the hair shaft and follicle are involved, topical antifungals are not effective. Oral Griseofulvin is still the treatment of choice.

Tinea corporis can occur on almost any part of the body. Small areas may respond well to topical antifungals, whereas large areas or treatment failures may need oral antifungals. There are numerous topical antifungals that are OTC or require a prescription. The OTC antifungals (miconazole, clotrimazole) are significantly less expensive and are equally effective for most cutaneous fungal infections. Whereas most topical antifungals treat dermatophytes and Candida, Nystatin treats Candida only. Therefore Nystatin has no role in the treatment of a suspected dermatophyte.

Tinea cruris may be red and scaling without the central clearing seen in tinea corporis. It should also be differentiated from Candida which may be more red and have satellite lesions, and erythrasma which is more brown and has coral-red fluorescence with ultraviolet light. Topical or systemic antifungals may be used depending upon the severity of involvement. If you are uncertain if there is Candida involvement, it is best to choose an antifungal agent that covers both dermatophytes & Candida (not Tinactin or Naftin).

Tinea pedis may be seen as macerated white areas between the toes or as dry red scaling on the soles or sides of the feet (moccasin distribution). It can be treated with the same topical or oral antifungals used for tinea corporis or cruris. Griseofulvin or the newer oral antifungals may be used when the lesions are not responding to topical agents.

Onychomycosis is a fungal infection of the nails. Until the release of the newer oral antifungal agents (itraconazole, terbinafine) the success rate for eradication of nail fungus was poor. The newer agents can be give for short treatments of 3 months or given as pulse therapy one week a month for 3-4 months. They are costly and have cure rates of approximately 70%.

It is important to establish a definitive diagnosis of onychomycosis before starting treatment with oral antifungals because there are other causes for dystrophic nails such as psoriasis, lichen planus, and trauma. Before prescribing oral antifungal agents, it is important to go over the risks and benefits of these medications with your patients. Itraconazole and terbinafine are more effective than griseofulvin and do offer more hope than before to patients suffering with painful or dystrophic nails with a fungal etiology.