Infections of the Integumentary System, Soft Tissue, and Muscle

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Infections of the Integumentary System, Soft Tissue, and Muscle



Hands are one of the most efficient and direct instruments for transferring microbes and/or pathogens to the main port of entry in the body—the mouth. They are also one of the most efficient and direct methods for pathogens to be collected and subsequently transferred to other ports of entry, such as breaks in the skin. The average person carries between 10,000 and 10 million bacteria per hand. Ignaz Semmelweis (July 1, 1818 to August 13, 1865), a Hungarian physician, is one of the first practitioners to understand and connect the relationship between hands and the transfer of bacteria to portals of entry. His assessment of the cause and the use of the information helped to cure the ravages of puerperal (childbed) fever. The current medical practice of that time (mid-1800s at about the same time the germ theory of disease was being formulated) was for physicians to proceed directly from an autopsy to the live patient without washing anything, least of all hands. In fact, the crusts of blood, pus, and some necrotic tissue residues were wiped on and left on the lapels of their coats to show they had “experience.” In addition, the medical bureaucracies were highly resistant to any changes in their established practices that did not include anything resembling hygiene, but did include belief in miasmas (“bad air”) and balance of the “four humours” (see Why You Need to Know: History in Chapter 2, Chemistry of Life). Actually, the miasmas were generated from the stench of rotting flesh from dead tissues and cadavers. The germ theory of disease had not yet been developed. Then a fellow physician and close friend of Semmelweis died from a scalpel wound with symptoms not unlike those of patients with puerperal fever.


Ignaz Semmelweis postulated that the odor came from some residue on the patients or cadavers and that if this was removed then the puerperal fever might be altered. He extended his washing to remove the stench and included instruments used to examine patients and cadavers, medical students’ hands, midwife personnel, and all who came in contact with puerperal fever. The results were dramatic. Death rates in the wards and elsewhere plummeted from more than 30% to 1%! Yet, the “establishment” was unwilling (see Semmelweis reflex, below) to accept the cause of death and dying from puerperal fever as a result of their time-honored practices. Finally, the wisdom and evidence of Semmelweis, Koch, Pasteur, Lister, and others prevailed during the mid- to late 1800s as the germ theory gradually became accepted.

Joseph Lister (April 5, 1827 to February 10, 1912), “the father of modern antisepsis,” was aware of the work of Semmelweis and that of other germ theory advocates; however, he used carbolic acid (phenol) instead of chlorinated soaps to disinfect hands, surgical instruments, and operating fields. Carbolic acid was used to deodorize sewage and his reasoning, like that of Semmelweis, was to get rid of the source of the odor. In addition, one of Lister’s nurses developed contact dermatitis to the carbolic acid and he had Charles Goodyear make rubber surgical gloves for protection. He further acknowledged Semmelweis’s earlier work by stating, “Without Semmelweis, my achievements would be nothing.”


Bureaucratic rejection without examination of experimental evidence has given rise to the “Semmelweis reflex” or dismissal out of hand, as an automatic reflex to new, challenging ideas without the benefit of thought or experimentation.

Soaps and detergents are definitely effective tools to slow down or prevent transmission of microbes. The development of antimicrobacterial soaps has led to the use of these products in most households, public places, and in the healthcare environment. While the use of these antibiotic products is essential in healthcare facilities, concern is growing over the overuse of antibacterial household cleaning and hygiene products for fear of the possible development of antimicrobial drug resistance. Appropriate hand washing with regular soap and water has proven effective under most circumstances. The Centers for Disease Control and Prevention, in conjunction with many scientific groups, is currently studying the possible consequences of overuse of certain antibacterial products.


The skin provides an efficient, significant barrier against invading microbes and thus represents the first line of defense against infection (see Chapter 20, The Immune System). The human skin and mucous membranes host many bacterial species as part of their normal flora (see Chapter 9, Infection and Disease). Although these organisms normally do not cause infections in intact skin, any break in the skin can lead to a range of infections, from treatable to life-threatening skin conditions. There are many types of skin infections caused by different organisms such as bacteria, viruses, fungi, and parasites. Microbial disease of the skin may result from the following:

Persons with certain conditions or diseases can be at greater risk for such infections; such people include but are not limited to those with:

To understand the different types of skin infections and infections of the underlying tissue it is important to understand tissue structure. The skin is composed of three layers: the epidermis, dermis, and subcutaneous tissue or hypodermis (Figure 10.1).

• The epidermis is composed of five layers of epithelial tissue, where the cells are constantly formed by the innermost layers through mitosis. Within the epidermis are Langerhans cells, which are dendritic cells that play a role in defense against invading microbes (see Chapter 20, The Immune System).

• The dermis consists of two layers: the superficial papillary layer (closest to the epidermis) and a deeper reticular layer. The papillary layer is composed of loose connective tissue and contains blood capillaries that service the epidermis and cutaneous receptors. The reticular layer consists of irregular dense connective tissue surrounding blood vessels, hair follicles, nerves, sweat glands, and sebaceous glands. The epidermis is anchored to the dermis by a basement membrane.

• The hypodermis or subcutaneous layer is made of loose connective tissue with abundant adipose (fat) cells.

Skin Manifestations of Systemic Bacterial and Fungal Infections

Disease Cause Skin Manifestation
Toxic shock syndrome Staphylococcus aureus and some streptococci Rash and desquamation due to bacterial toxin
Scarlet fever Streptococcus pyogenes Erythematous rash caused by bacterial erythrogenic toxins
Syphilis Treponema pallidum Disseminated infectious rash in the secondary stage of the disease
Enteric fever Salmonella typhi “Rose spots” containing bacteria
Meningitis, septicemia Neisseria meningitidis Petechial or maculopapular lesions containing bacteria
Septicemia Pseudomonas aeruginosa Ecthyma gangrenosum

Macular or hemorrhagic rash Blastomycosis Blastomyces dermatitidis Papule or pustule development into granuloma lesions containing fungus Cryptococcosis Cryptococcus neoformans Papule or pustule most commonly on the face or neck


Bacterial Infections

Bacterial infections of skin, soft tissue, and muscle can be classified on an anatomical basis, depending on the layers of skin and soft tissue involved:

• Abscesses: An abscess is a localized collection of pus in an area of tissue that is infected. It is a defensive mechanism of the body to prevent the spread of infectious material to other areas of the body. Abscesses can occur in any kind of solid tissue but most frequently on the skin surface, where they are easily visible. They may be superficial pustules or pimples, furuncles or boils, carbuncles or pyogenic groups of hair follicles, and deep skin abscesses.

• Spreading infections: Can be limited to the epidermis, such as is the case for impetigo, or can involve the subcutaneous fat, as in cellulitis.

• Necrotizing infections: These infections result in the death of the infected tissue (necrosis). Some of these infections spread with alarming rapidity (i.e., “flesh-eating bacteria”) along the surface of the muscles, causing an interruption of blood flow. Because the immune system uses the bloodstream for the purposes of defense, the cells of the immune system and their antibodies cannot reach the infected area; hence the infection can spread rapidly and may be difficult to control. In the case of a necrotic infection, death is not uncommon, even with the appropriate treatment.

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 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 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.

Acute Necrotizing Fasciitis

Necrotizing fasciitis (“flesh-eating bacteria”; see Medical Highlights) is an uncommon infection of the deep layers of the skin and subcutaneous tissue. Although a mixture of aerobic and anaerobic bacteria is often present at the original site of infection, the severe inflammation and tissue necrosis seem to be due primarily to the actions of a highly virulent strain of Streptococcus pyogenes (gram-positive, group A β-hemolytic Streptococcus), the organism responsible for “strep throat.” These infections typically originate in the mucous membranes (e.g., the throat) or skin. Necrotizing fasciitis is a progressive, rapidly spreading, inflammatory infection causing secondary necrosis of subcutaneous tissue and adjacent fascia. Proteases, which are tissue-destroying enzymes released by the pathogen, are the cause of the necrosis. The infected area becomes noticeably inflamed, painful, and enlarged, and symptoms of dermal gangrene are apparent. Systemic toxicity accompanied by fever, tachycardia, hypotension, mental confusion, disorientation, and possibly organ failure occur. Immediate and aggressive treatment is essential, including surgical removal of all infected tissue, accompanied by aggressive antimicrobial therapy, fluid replacement, and possible amputation to prevent further spread of the infection. The mortality rate is estimated to be 40% to 60%.