Staphylococcal Infections

Staphylococcal infections are among the most common bacterial skin infections. Staphylococci are part of the normal flora on the skin and in the nose of healthy adults. In general, these bacteria do not cause harm, except when there is a break in the skin, burns, or other injuries allowing the organism to enter through the mechanical skin barrier and cause infection. Staphylococcal infections range from mild to life-threatening. People susceptible to staphylococcal infections include newborns, breastfeeding women, people with skin disorders, and people with a weakened immune system, such as those with diabetes and cancer.

Furuncles (Boils)

Staphylococcus aureus is the most common cause of boils and persons who are carriers of the virulent strain of Staphylococcus aureus often go through recurrent boils. Exposure to Pseudomonas aeruginosa and/or Pseudomonas folliculitis in hot tubs or swimming pools may also lead to furuncles. The infection begins in a hair follicle (folliculitis) and subsequently spreads into the surrounding dermis (Figure 10.2). Furuncles can occur in the hair follicles anywhere on the body but are most commonly found on the face, neck, armpit, buttocks, and thighs. At first the lesion presents itself as a firm, red, painful nodule and then develops into a large, painful mass that often drains large amounts of pyogenic exudate (pus). Collections of furuncles can fuse to form carbuncles, a large infected mass, which may drain through several sinuses or develop into an abscess. Drainage to the inside can result in access of the bacteria to underlying sites, which can then be the cause of serious infections such as peritonitis, empyema, meningitis, or systemic poisoning (septicemia). Furuncles may heal on their own if they drain properly. Warm moist compresses encourage furuncles to drain and therefore speed up the healing processes. Deep or large lesions most often need to be lanced or drained surgically.

Cellulitis

Cellulitis is an acute infection of the dermis and subcutaneous tissue usually caused by Staphylococcus aureus, streptococci, or other bacteria. The origin of the infection is either a superficial skin lesion such as a boil or ulcers resulting from trauma. Cellulitis is characterized by redness, swelling, warmth, and pain or tenderness and develops within a few hours or days of the trauma. It occurs most commonly on the lower legs (Figure 10.3) and the arms or hands, but other areas of the body may be involved. Regional lymph nodes become enlarged and the patient suffers malaise, chills, and fever. Systemic antibiotics as well as local compresses and analgesics are usually necessary.

Impetigo (Pyoderma)

Impetigo is a superficial skin infection limited to the epidermis, common in infants and children. People who play contact sports (e.g., football, wrestling) are also susceptible, regardless of age. Staphylococcus aureus is an organism that can cause highly contagious infections such as impetigo in neonates, causing a threat in neonatal care units. In older children impetigo may also be caused by group A β-hemolytic streptococci. Scratching, direct contact with hands, eating utensils, or towels can easily be vectors to spread the infection. Lesions start with red or pimple-like sores most commonly on the face, arms, and legs. The small vesicles rapidly enlarge, fill with pus, and subsequently rupture to form yellowish-brown crusty masses (Figure 10.4). Because of autoinoculation with hands, towels, and clothes, additional vesicles develop around the primary site of infection. The treatment of impetigo depends on the age of the child and the severity of the infections and may include hygienic measures, topical treatment, and oral antibiotics in more severe cases.

Streptococcal Infections

Most often streptococcal skin infections are secondary to a primary lesion caused by another organism. Streptococci can cause cellulitis and impetigo as described previously. Although uncommon because of antibiotic treatment, glomerulonephritis may occur after streptococcal infections.

Erysipelas

Erysipelas is a type of acute infection generally caused by group A Streptococcus. Historically, the face was the most commonly involved site of infection, but now it accounts for approximately 20% of cases and the legs are most often affected (Figure 10.5). Erysipelas can be distinguished from cellulitis by the raised advancing edges and sharp borders. In general, oral antibiotics such as penicillin (see Chapter 21, Pharmacology, and Chapter 22, Antimicrobial Drugs) are used to treat the infection; however, severe cases, with complications such as bacteremia (bacteria in the blood), might require the use of intravenous antibiotics.

Acne

Acne is caused by Propionibacterium acnes, a bacterium present on the skin of most people. It lives on fatty acids secreted by sebaceous glands, which in adolescence have increased activity due to hormonal changes (Figure 10.6). This excessive amount of sebum released results in the formation of whiteheads and blackheads, and the breakdown of sebum by P. acnes causes local inflammation and the eruption of pimples, sometimes causing skin lesions (folliculitis) that can result in permanent scar formation. P. acnes can be treated with antibiotics and antibacterial preparations; however, tetracycline-resistant P. acnes is becoming common.

Leprosy

Leprosy (Hansen’s disease) is caused by Mycobacterium leprae and previously affected millions of people worldwide. Although leprosy still represents a health problem in parts of Africa, Asia, the South Pacific, and some South American countries, according to the World Health Organization (WHO) the global number of new cases detected annually has decreased dramatically, and continues to do so. Leprosy is not highly contagious and prolonged exposure to a source is necessary for infection. Transmission of the infection is related to overcrowding and poor hygiene; it generally occurs by direct contact and aerosol inhalation. The clinical manifestations vary but generally affect the skin, mucous membranes, and nerves (see Chapter 13, Infections of the Nervous System and Senses). The chronic disease is classified as borderline, paucibacillary, or multibacillary leprosy.

• Borderline leprosy is the most common form; the skin lesions, or macules, resemble those of tuberculoid leprosy (i.e., hypopigmented areas without feeling, due to destruction of nerve tissue by the immune response) but are more numerous and irregular.”

• Paucibacillary leprosy is characterized by one or more hypopigmented skin macules and damaged peripheral nerves, resulting from attack by inflammatory cells of the immune response.

• Multibacillary leprosy is associated with symmetric skin lesions, nodules, thickened dermis, and damage to the nasal mucosa (Figure 10.7).Typically there is no loss of feeling because patients with this form of leprosy do not mount an effective immune response.

The mechanism of pathogenicity is relatively unknown because the organism cannot be grown on artificial culture medium, making it difficult to study in the laboratory environment. Laboratory diagnosis of M. leprae therefore depends on microscopic examination of skin biopsies. Treatment of leprosy includes antibiotics, rehabilitation, and education. In the case of immunocompromised patients drug treatment might be required over the entire lifetime. An overview of bacterial skin infections is given in Table 10.1.

Warts

Warts are the result of a common viral infection caused by the human papillomavirus (HPV). They are generally small, rough tumors, most often located on the hands and feet.

The virus is transmitted by direct contact with an individual or by fomites such as a towel. Autoinoculation is sometimes responsible for the spreading of warts in an individual. Different types have been identified according to shape (Figure 10.8), site affected, and type of HPV:

Warts in children and adolescents often disappear on their own. The treatment of warts depends on their length of time on the skin, location, type, and also their severity. Treatment may include the application of salicylic and lactic acid to soften the infected area, freezing the wart with liquid nitrogen, electrodesiccation, or laser surgery.

Herpes Simplex Infections

Herpes infections generally manifest themselves as painful, watery blisters in the skin or mucous membranes of the lips, mouth, or the genitals (Figure 10.9). The herpes simplex virus has two strains: herpes simplex virus 1 and 2 (HSV-1 and HSV-2). HSV-1 usually causes infections on the lips and in the mouth (fever blisters), whereas HSV-2 is primarily responsible for genital herpes. It should be noted that both strains can potentially infect both general regions. All herpesviruses have the capacity to remain latent in the ganglia of the sensory fibers innervating a particular area of the skin. Subsequent infections therefore have the tendency to appear in the same areas. HSV is transmitted by direct contact of lips or genitals during the time when the sores are present or just before they appear. The mechanism(s) of reactivation of the virus are poorly understood but several factors have been identified to cause reoccurrence: ultraviolet light, x-rays, heat, cold, hormonal imbalance, and emotional or other stress factors. Herpes can also be transmitted during childbirth and the disease can be fatal to the infant. Both viruses can also cause morbidity and mortality in an immunosuppressed person.

Treatment is available in the form of antiviral medications, which reduce the duration of the symptoms and accelerate healing, but do not cure the condition or limit the ability of the virus to establish latency or recurrent infections.

Varicella-Zoster Infections

The varicella-zoster virus (VZV), a herpesvirus, is the causative agent for chickenpox, and when recurring later in life it causes herpes zoster, also called shingles. This virus is transmitted by respiratory droplets or by any contact with secretions of the respiratory tract of an infected individual. Therefore the primary infection begins in the mucosa of the respiratory tract, and then progresses by the bloodstream throughout the body and to the skin. VZV has some characteristics in common with HSV, such as the ability to create latent infections of neurons, and therefore having the ability to cause recurrent disease and the formation of blister-like lesions.

The primary disease caused by VZV is chickenpox, which is usually relatively mild in children but more severe if it affects adults. Because the virus is latent, it can be reactivated in older adults or in people with impaired immunity. Once reactivated, the virus replicates along the neural pathways and infects the skin, causing a characteristic rash along the entire dermatome (Figure 10.10).

Molluscum Contagiosum

Molluscum contagiosum is caused by a poxvirus, the molluscum contagiosum virus or MCV. This viral skin infection causes raised, pearl-like papules or nodules in the skin and is common in children. Lesions in children are frequently apparent on the face, neck, armpit, arms, and hands, but may occur anywhere on the body except the palms and the soles. The virus is contagious and in children is transmitted through direct contact, saliva, or shared articles of clothing, including towels. In adults, molluscum infections are most often spread by sexual contact and usually affect the genitals, lower abdomen, buttocks, and inner thighs. The skin lesions are flesh-colored, dome-shaped, pearly in appearance, and generally not painful, but can itch or become irritated. Molluscum lesions in people with normal immune systems may disappear in 6 to 9 months but can also persist through autoinoculation. The lesions may be extensive in people with AIDS or other conditions that affect the normal functioning of the immune system. Treatment, if necessary, depends on the patient’s age, overall heath, and medical history; on the location and number of lesions; and involves a variety of topically applied substances as well as cryosurgery and laser therapy.

Roseola Infantum

Roseola infantum or sixth disease is caused by human herpesvirus type 6 (HHV-6) and HHV-7 (roseolovirus). It is a self-limiting disease affecting children between 6 months and 3 years of age and is characterized by a high fever of 102° F to 104° F (39° C to 40° C) and a generalized body rash. In some cases, the high fever can cause febrile convulsions due to a sudden rise in body temperature. Once the fever subsides, after 3 to 5 days the rash appears, usually starting on the trunk and spreading to the limbs. The rash disappears within hours to a day.

Smallpox

Smallpox is an acute contagious disease caused by the variola virus, a member of the orthopoxvirus family. It is one of the most devastating diseases known to humans and for centuries epidemics swept across continents, drastically reducing the population. The virus can be spread from person to person by contact with skin lesions or via secretions of the respiratory tract. The disease, for which no effective treatment has been developed, kills approximately 30% of the infected population. Survivors show characteristic deep pitted scars (pockmarks), which are most prominent on the face. The incubation period is usually 12 to 14 days and is followed by the sudden onset of influenza-like symptoms such as fever, malaise, headache, prostration, and severe back pain; when the digestive system becomes involved, abdominal pain and vomiting occur. A few days later, when the body temperature falls, the characteristic pimples associated with the disease start to erupt in the mouth, arms, and hands and later on the rest of the body (Figure 10.11). These pimples, now called macules, are still small but the patient is at the most contagious stage.

In 1967 the WHO started a campaign to eradicate smallpox by vaccination (originally developed by Edward Jenner) with a live attenuated strain of the vaccinia virus. After successful vaccination campaigns throughout the world, the WHO certified the eradication of smallpox in 1979. Cultures of the virus are kept by the Centers for Disease Control and Prevention (CDC) in the United States and at the Russian Vector Institute for Virology in Novosibirsk, Siberia. Concern about the use of smallpox by bioterrorists resulted in the preparation of contingency plans by many countries to deal with potential threats (see Chapter 24, Microorganisms in the Environment and Environmental Safety). These plans include the stockpiling of the smallpox vaccine. In December 1999, the WHO Advisory Committee on Variola Virus Research concluded that the then current vaccine supplies to prevent and control a smallpox outbreak were limited. As a result, a number of governments have chosen to examine their stocks, test their potency, and consider whether more vaccine is required. At present, the United States has a big enough stockpile of the smallpox vaccine to vaccinate everyone in the United States in the event of a smallpox emergency (CDC information).

Tinea Capitis

Tinea capitis is an infection of the scalp causing itchy, red areas, destroying the hair and leaving bald patches. This infection is common in school-aged children and may result from infection with Microsporum canis, transmitted by cats and dogs, or by Trichophyton tonsurans, which is transmitted by humans. The infection can also be transmitted by infected items (fomites) such as hats, combs, clothing, or other such objects. Oral antifungal medications are recommended for treatment.

Tinea Corporis

Tinea corporis affects the body almost anywhere; on the arms, legs, or chest, in particular on nonhairy parts. The lesion is characterized by a round, erythematous ring of vesicles or papules with a clear center, customary for “ringworm” infections. Symptomatic pruritus or a burning sensation is not unusual. Tinea corporis is contagious and can be acquired from infected individuals; through contaminated items, shower floors and walls, as well as pool surfaces. The infection can also be spread by pets, in particular by cats. Topical, over-the-counter antifungal medications are often effective. Severe or chronic infections may require oral antifungal medications, and antibiotics may be given to prevent secondary bacterial infections. Furthermore, if transmitted by a pet, the pet should also be treated.

Tinea Versicolor

Tinea versicolor is caused by the yeast Malassezia furfur (formerly Pityrosporum ovale) and is commonly found on the human skin; it is therefore not contagious to others. The pathogenicity of this particular fungus seems to be associated with a change from its yeast form to the hyphal form, which occurs under special conditions such as in warm and humid environments. This fungal infection often affects the skin of young people, and spots are commonly present on the back, underarms, upper arms, chest, lower legs, and neck. The spots produced are either reddish-brown or lighter than the surrounding area. In people with dark skin tones, hypopigmentation is common, and in people with lighter skin color hyperpigmentation is more common. Treatment includes over-the-counter topical applications, but in severe cases prescription-strength topical and/or oral medication might be required. Although tinea versicolor does not leave permanent skin discoloration, the skin may remain uneven in color for several weeks, even after successful treatment.

Tinea Cruris

Tinea cruris is a fungal infection of the groin area and is commonly referred to as “jock itch.” The infection occurs most commonly in adult men and can be triggered by friction from clothes and prolonged wetness in the groin area as occurs during sweating. The condition causes itching and a burning sensation and the affected area may appear red, tan, or brown, with flaking, peeling, or cracking skin. Tinea cruris can be passed from one person to the next by direct skin-to-skin contact or by contact with unwashed clothing such as athletic supporters; hence the term “jock itch.” The condition usually responds to self-care within 2 weeks if the skin is kept clean and dry, topical over-the-counter antifungal or drying powders are applied, and tight damp clothing is avoided.

Tinea Unguium

Tinea unguium, also called onychomycosis, infects the nails, particularly the toenails. The infection can occur directly in the nail itself or can result from an untreated fungal infection of the foot. Tinea unguium produces nails that look white and opaque, and are thick and brittle. People at risk for this infection are those with diabetes and/or peripheral vascular disease, older women, and people of any age who wear artificial nails. In addition, people who are required to wear close-fitting rubber footwear at work and people living in a warm humid climate are also more likely to acquire this infection.

Treatment might require several months and usually includes oral antifungal medication as well as local fungicides. Onychomycosis is difficult to cure and may return even after treatment.

Tinea Pedis

Tinea pedis, commonly called “athlete’s foot,” thrives in warm and humid conditions. The infection is most frequently due to Trichophyton rubrum, T. interdigitale, and Epidermophyton floccosum. Of all the tinea infections, athlete’s foot is the most common. It generally causes cracked, flaking, peeling skin between the toes and the affected areas are commonly red. Itchiness, burning, or stinging and blisters, oozing, or crusting may occur as well (Figure 10.13). The infection may also spread to the heels, palms, and between the fingers. Athlete’s foot is contagious and can be obtained through direct contact or fomites such as shoes, stockings, showers, or pool surfaces (see Life Application: Athlete’s Foot). The afflicted feet may have a foul odor and secondary bacterial infections are not uncommon, which adds to the inflammation and possible necrosis. Over-the-counter antifungal powders, sprays, or creams can help to control the infection.

Chromoblastomycoses

Chromoblastomycosis is a chronic localized infection of the subcutaneous tissue characterized by verrucoid lesions of the skin, usually located in the lower extremities. It is limited mostly to the subcutaneous tissue without involvement of bone, tendon, or muscle. The original site of infection may be very small, often caused by vegetative material such as thorns or splinters, and the infection builds at the site over a period of months or years. Small red papules will appear but the lesions are usually not painful and patients often do not seek medical care. Satellite lesions may occur as the disease develops; the rashlike areas may enlarge, become raised irregular plaques, and sometimes become tumors with a cauliflower-like appearance. Although the prognosis for small lesions is good, severe cases of the infection are difficult to cure. Some antifungal drugs given orally and cryosurgery have been shown to have some effectiveness. Antibiotics may be given to prevent and/or treat bacterial superinfections, which may occur as a result of these mycoses.

Mycetomas

Mycetoma is a chronic infection that begins as a subcutaneous nodule after injury and may penetrate deeper into the tissue, sometimes even to the bone. Mycetoma may be caused by several fungi and/or actinomycetes, which are bacteria that, like fungi, form filaments. Both types of organisms are found in the soil and on plant material of tropical regions, and are often associated with injuries of the feet. As the infection progresses from the original site it characteristically swells and the middle of the lesion caves in, ulcerates, and discharges pus and grains. Eventually sinus tracts (holes) form, which also are pyogenic with grains that are filled with the microorganism. Considerable deformity occurs, which makes walking difficult. Furthermore, mycetoma may cause itching or burning sensations along with secondary bacterial infections, which are common. Because of the wide range of causative microorganisms, the treatment of mycetoma depends mainly on its etiological agent and the extent of the disease. Treatment with combinations of drugs over extended periods of time has met with some degree of success; however, severe infections may require more heroic interventions such as amputation of the infected foot or hand.

Sporotrichosis

Sporotrichosis, the third general class of subcutaneous mycoses, is caused by Sporothrix schenckii, a fungus found in the soil, in sphagnum moss, hay, and other plant material in all parts of the world. The fungus enters the skin through small cuts or punctures from thorns, barbs, pine needles, or wires. At risk are people working with thorny plants, sphagnum moss, and hay. The fungus is not spread by person-to-person contact. Initial symptoms are small painless bumps resembling insect bites and can be red, pink, or purple. The bump occurs at the site of fungal entry, usually on a finger, hand, or arm. Additional bumps follow that resemble boils, and heal very slowly. The occurrence of the initial bump may be any time from 1 to 12 weeks after exposure; however, in most instances they appear within 3 weeks. The infection usually spreads along cutaneous lymphatic channels of the involved extremity. Sporotrichosis formerly was treated with oral potassium iodide and now most often with itraconazole, a new drug with fewer side effects. Sporotrichosis can usually be prevented by wearing gloves and long sleeves when working with plant or wire material that can prick the skin. Skin contact with sphagnum moss should be avoided because it has been implicated as a source of the fungus in a number of outbreaks, especially in plant nurseries.