Table of Contents   This Chapter   All Chapters

GRAM-POSITIVE INFECTIONS

Impetigo

Etiology and pathogenesis

Impetigo represents a superficial infection of the skin by either Staph. aureus or Strep. pyogenes , with Staph. aureus being more commonly found (Table 24.1). Combined infections are seen. A bullous form occurs and is almost always caused by toxin-producing Staph. aureus (see staphylococcal scalded skin, later, for discussion of the toxin). Chicken pox, insect bites, abrasions, lacerations, and burns commonly precede non-bullous impetigo. It may occur secondary to scabies. Patients with atopic dermatitis are usually highly colonized with Staph. aureus and are at increased risk for impetigo.

Clinical

A tiny pustule or vesicle forms initially and then rapidly spreads out to form the typical honey-colored, crusted lesion. It is commonly found on the face, especially below the nostrils (Fig.24.1), but it may occur anywhere (Figs 24.2 and 24.3). Lesions may be bullous (Fig.24.4), pustular, crusted, or mixed. Pain, surrounding erythema, and constitutional symptoms are usually absent. Regional adenopathy is common. The term ecthyma (Fig.24.5) is used to describe multiple, circular or oval ulcers covered by a hard, brown, dried crust on the legs caused by group A b -hemolytic streptococcus, Staph. aureus , or both. As with other streptococcal infections, acute glomerulonephritis may occur.

Figure 24.1 Impetigo of the face. The face is a common location for impetigo. The area below the nose is particularly prone, presumably because staphylococci often colonize the nose. Any nasal drainage promotes infection.

Figure 24.2 Widespread impetigo in a child. Children are commonly affected by impetigo. If untreated, the infection can become widespread.

Figure 24.3 Impetigo. Multiple eroded lesions on the buttocks. A bacterial culture showed Staphylococcus aureus. The clinical appearance mimicked herpes simplex, emphasizing that, at times, distinguishing bacterial impetigo from herpes simplex is impossible.

Figure 24.4 Bullous impetigo. Both small vesicles and large bullae may occur in impetigo. The separation occurs high up in the epidermis, leading to flaccid bullae.

Figure 24.5 Staphylococcus aureus. Multiple, circular or oval ulcers covered by a hard, brown, dried crust on the legs caused by group A ?-hemolytic streptococcus, Staphylococcus aureus, or both is characteristic of ecthyma.

Differential diagnosis

The diagnosis is usually obvious, but herpes simplex infection can present as an acute, crusted lesion. Autoimmune bullous disorders often have a crusted component, but most cases are in the older adult population. Swabs for bacteriology will prove the diagnosis; serology (DNaseB) is less commonly performed for retrospective confirmation.

Treatment

Topical mupirocin or fusidic acid three times a day for 7 days may be given for localized disease, although they probably should not be used around the mouth, as they may be licked off. Fusidic acid-resistant staphylococci are common in some localities. For widespread involvement, an oral antibiotic should be used, usually a cephalosporin (e.g. cephalexin) or a b -lactamase-stable penicillin (e.g. cloxacillin, dicloxacillin, or co-amoxiclav). In many regions, a significant percentage of Staph. aureus strains are erythromycin-resistant, and therefore this antibiotic is not recommended routinely, although it may be useful in penicillin-allergic patients if the bacterial sensitivities are known. For the elimination of Staph. aureus nasal carriage, mupirocin or bacitracin instilled in the nose twice a day for 5 days is sufficient.

    Note that this condition is very infectious. It is logical, even if poorly evidence-based, to soak off crusts (which oral antibiotics won't penetrate) and to apply an antiseptic to reduce transmission.

Perianal dermatitis

Etiology and pathogenesis

Also called perianal cellulitis, this disease represents an infection of the perianal skin by streptococci. A well-demarcated perianal erythema that may be accompanied by itching, bleeding, and painful defecation is characteristic (Fig.24.6). Children aged 7 months to 8 years are most commonly affected, but adults may also be affected. It has recently been suggested that group A b -hemolytic streptococcus (GABHS)-induced vulvovaginal and penile infections should be grouped together with perianal dermatitis under the inclusive term perineal streptococcal disease , because these conditions coincide, share important clinical characteristics, and therefore represent manifestations of the same disease. A skin swab culture showing GABHS is diagnostic. Perianal dermatitis has been known to precipitate guttate psoriasis. Penicillin, cephalosporins, erythromycin, or topical mupirocin may be used for treatment.

Figure 24.6 Perianal dermatitis.

Bacterial folliculitis

Etiology and pathogenesis

Folliculitis refers to infection of individual follicles (more extensive follicle-based infection, termed furunculosis, is discussed later). The most common offending organism is Staph. aureus . Colonization of the nose followed by dissemination on to the skin is a typical pattern.

Clinical

Multiple follicular pustules scattered on the trunk or extremities (Figs 24.7 and 24.8) may represent a bacterial folliculitis. Lesions may be deep-seated and appear only as erythematous papules without a pustule. Excoriations may also mask the primary pustule. Culture establishes the diagnosis and may indicate the appropriate antibiotic choice. Bacterial folliculitis of the vertex of the scalp (Fig.24.9) occurs, most commonly in dark-skinned patients.

Figure 24.7 Bacterial folliculitis. A pustule pierced by a hair.

Figure 24.8 Bacterial folliculitis of the chest. A bacterial folliculitis may occur on almost any part of the body. Grouped or scattered red papules and some pustules are typical.

Figure 24.9 Bacterial folliculitis of the scalp. The vertex of the scalp is prone to infection by Staphylococcus aureus, particularly in dark-skinned patients. Aggressive oral antibiotic treatment is needed until the lesions clear.

Differential diagnosis

Many organisms may cause folliculitis, and there are several other causes. The differential diagnosis of folliculitis or follicular pustules is listed in Table 24.2.

Treatment

An oral antibiotic as directed by culture should be given. The usual pathogen is Staph. aureus , so appropriate empiric therapy may be begun after sending a specimen for culture. It should be clear from the differential diagnosis list that it is good practice to identify a cause: many patients are subjected to many courses of antibiotics but do not actually have staphylococcal folliculitis. If chronic folliculitis is swabbed after failed treatment, there is a risk of the antibiotics causing a false negative result. Clean the skin, pierce the pustule with a sterile needle, and swab the pus content.

    For those with persistent or recurrent furunculosis caused by Staph. aureus , the following regimen may be tried (doses for an adult):

PRACTICE POINTS

Furuncles, carbuncles, and boils

Etiology and pathogenesis

The term furuncle is used when the erythema of inflammation from a bacterial infection extends well beyond the follicle. A carbuncle is a larger mass of infection that exudes pus from multiple follicles. A boil is an inflammatory nodule that, if untreated, ruptures, exudes pus, and slowly heals; in common usage, this term may include furuncles, carbuncles, abscesses, and infected cysts.

    Low serum iron has been associated with chronic furunculosis, as this deficiency may impair oxidative killing by neutrophils.

Clinical

An acute, tender, inflamed nodule (Figs 24.10 and 24.11) may develop in the axilla or elsewhere, representing a local infection or abscess. After several days, the surface may thin, the nodule becoming fluctuant and then rupturing. Alternatively, the abscess may remain deep, being resorbed by the body. Chronic furunculosis may result from a Staph. aureus nasal carrier state or occur due to reinfection from family members.

Figure 24.10 A furuncle or a boil begins as a tender, inflamed nodule that usually becomes fluctuant, points, and ruptures.

Figure 24.11 Carbuncle on the nape of a diabetic man. This is a staphylococcal infection of several contiguous hair follicles.

Differential diagnosis

Treatment

Warm compresses twice daily may help bring the abscess to a head. Incision and drainage once the lesion becomes fluctuant is the primary therapy. Attempting to incise and drain too soon may lead to a bleeding incision but no pus. Oral antibiotics for the normal host are probably unnecessary if incision and drainage are performed. Daily hexachlorophene cleansing of the body and mupirocin to the nose and anus (for patient only or all family members) is usually effective in chronic cases. Rarely, chronic oral antibiotics may be needed.

Methicillin-resistant Staphylococcus aureus

Originally viewed as a hospital problem, infection by community-acquired MRSA is becoming more and more common (Fig.24.12). Traditional antistaphylococcal antibiotics are ineffective. Oral agents that might be effective include tetracycline, linezolid, or a combination of trimethoprim–sulfamethoxazole and rifampin. Intravenous vancomycin is an alternative. Topical mupirocin is often useful for cutaneous treatment. Any abscesses may need to be drained. Repeated cultures with sensitivity testing may be helpful. In general, local laboratories should be consulted for identification of strain (and therefore of a likely source); for specific therapeutic policies, which will depend on the sensitivities; and for contact tracing and local environmental control measures. The nose should be cultured, and both nose picking and skin scratching should be discouraged.

Figure 24.12 Abscess caused by methicillin-resistant Staphylococcus aureus (MRSA). Skin infection by MRSA is a growing problem. Culture and sensitivity testing is important to target effective antibiotic therapy. Draining of abscess, as was done here, is often necessary.

Wound infection

Wounds are more likely to become infected if foreign material or necrotic tissue is present, if the patient is immunosuppressed, if the area has a compromised blood supply, if the wound is under increased tension, and if the patient smokes. The key clinical differential is allergic contact dermatitis. An open wound will become red and inflamed, and drain pus (Fig.24.13). A closed infected space will become swollen and painful. Lymphadenopathy may occur. Any abscess should be drained, and a bacterial culture should be taken. An oral antistaphylococcal antibiotic should be started.

Figure 24.13 Wound infection. Note the erythema and drainage. The most common condition in the differential diagnosis is an allergic contact dermatitis to some component of the dressing. In that case, the skin is eczematous (e.g. red and scaly or microvesicular).

PRACTICE POINTS

Erysipelas and cellulitis

Etiology and pathogenesis

These two terms have become rather merged over the years. In theory, erysipelas is superficial dermal infection and cellulitis represents a larger, deeper, spreading infection of the skin. Some use erysipelas to refer to facial infection but cellulitis for other sites. Local spread of infection around a wound may also be termed cellulitis, but generally does not have the importance of the more serious and potentially life-threatening condition discussed here.

    The causes also vary. Local infection around a wound is usually staphylococcal, while infections around leg ulcers have many causes. Erysipelas of the face is streptococcal, although Haemophilus infection of the face in children still occurs in some countries where immunization with Hib vaccine is unavailable. The typical spreading erythema ascending the lower leg, with fever, swelling, and malaise, is most commonly streptococcal.

Clinical

Both facial erysipelas and lower leg cellulitis are associated with fever and malaise, usually preceding the cutaneous features.

    In facial erysipelas, there is central facial, sharply defined redness and swelling that may be unilateral initially but often becomes bilateral in a ‘butterfly' distribution.

    Lower leg cellulitis or erysipelas is characterized by the acute onset of a warm, erythematous, edematous plaque that each day enlarges several times to many centimeters (Figs 24.14–24.16). Swelling may be severe; blistering and necrosis may occur. Cellulitis of the face occurs on occasion (Fig. 24.17) and must be treated aggressively.

    There are several factors that put a patient at risk for both bacterial cellulitis and necrotizing fasciitis. They include toe web maceration or tinea pedis, impaired venous or lymphatic return, diabetes mellitus, atherosclerosis, non-steroidal antiinflammatory drug use, and a preexisting open lesion.

Figure 24.14 (a,b) Erysipelas on the face. The acute onset of a bright-red, warm, spreading, edematous plaque on the cheek may represent a bacterial infection, usually caused by streptococci. Fever or chills may accompany the rash, and pustules or skin breakdown may occur. Early and aggressive treatment is indicated, usually with intravenous antibiotics.

Figure 24.15 Erysipelas of the leg. (a) Note the open wound on the proximal thigh, which gave rise to this infection. The patient should be monitored closely for more severe skin changes (e.g. purpura, bulla, postbullous ulceration, necrosis, hypoesthesia, or fluctuance), which may suggest necrotizing fasciitis or pyomyositis. (b) Chronic lymphedema has predisposed to cellulitis in this elderly patient.

Figure 24.16 Lymphangitic streaking. After a mastectomy, this woman developed cellulitis of the forearm with subsequent lymphangitic streaking along the defective lymphatic system.

Figure 24.17 Cellulitis of the nose. Every year or so, this woman develops cellulitis of the nose and, if untreated, the cheeks. A pustule of rosacea may have precipitated this episode.

Differential diagnosis

The differential is that of an acute, extending red plaque (Table 24.3).

Treatment

The patient without significant systemic signs or severe skin changes may be treated expectantly with appropriate intravenous antibiotics, usually including benzyl penicillin for the streptococcal entities. If the affected area is small and localized, oral antibiotics may be given with close monitoring. Edema should be treated by elevation and, if persistent but the leg is comfortable, by compression bandages or stockings. It is essential to treat any tinea pedis, as recurrences are otherwise common.

    If there is no response to antibiotics within 24h, either by persistence of systemic signs or by progression of the skin lesion(s), then the possibility of necrotizing fasciitis or pyomyositis should be considered. Magnetic resonance imaging (MRI) may be helpful in distinguishing these entities and defining the extent of the infection.

Necrotizing fasciitis

Etiology and pathogenesis

Necrotizing fasciitis is a potentially life-threatening infection of the skin. If not treated aggressively, it may spread rapidly through tissue, leading to sepsis and death. It is also known as the ‘flesh-eating' disorder. Strep. pyogenes is the most common pathogen, but Staph. aureus , gram-negative organisms, and anaerobes may be found, and synergistic infection also occurs. Risk factors include trauma, diabetes, and renal impairment.

Clinical

Onset of disease may be fulminant (within hours), acute (within days), or subacute (over several weeks). Warm and increasingly painful induration of a portion of a limb, followed by dusky or violaceous discoloration, then bulla formation and necrosis is characteristic (Fig.24.18). The infection may spread quickly,and mortality rates are high, especially if treatment is delayed. A skin swab or culture of aspirated fluid or tissue is more likely to be positive than are blood cultures.

Figure 24.18 Necrotizing fasciitis. The so-called flesh-eating bacteria, group A ?-hemolytic streptococcus, can cause significant tissue destruction rapidly. This 32-year-old woman developed pain, erythema, and swelling of the foot followed by necrotic ulceration over a week. There was no history of trauma. (Courtesy of Roger Bitar, M.D.)

Features that suggest this possibility are listed in the Practice point box.

Differential diagnosis

The differential is that of an acute necrotic plaque:

Treatment

Systemic antibiotics are not enough. Extensive surgical debridement is necessary. MRI may be helpful in some cases to delineate the extent of the infection. Fulminant cases have the worst prognosis, with a significant risk of death, especially when multiple organ failure and respiratory distress ensue. Because there is a high bacterial load, which may inhibit the action of penicillins, vancomycin is generally included in the therapy of the cases due to streptococci.

PRACTICE POINT

Warning signs of necrotizing fasciitis and the need for urgent surgical debridement in a patient with presumed lower leg streptococcal cellulitis include:

Staphylococcal scalded skin syndrome

Etiology and pathogenesis

This disease of young children is caused by a focus of infection by Staph. aureus that secretes an exfoliating toxin. The target for the toxins has recently been identified as desmoglein-1, a desmosomal glycoprotein that plays an important role in maintaining cell-to-cell adhesion in the superficial epidermis (it is the same protein that is targeted by the abnormal immune reaction in pemphigus). The toxin cleaves the extracellular domain of desmoglein-1, resulting in disruption of intercellular adhesion and formation of superficial blisters. A recent study showed that Staph. aureus cultured from the skin was non-toxin-producing in 69% of cases. Therefore the true offending staphylococcus was somewhere else in the body. The correct diagnosis is based on the clinical picture rather than laboratory studies.

Clinical

The infant or child may first develop a prodrome of fever and a sore throat. Within 48h, extremely tender flaccid bullae, which are Nikolsky sign-positive, develop. The bullae enlarge and rupture easily to reveal a moist erythematous base, which gives rise to the scalded appearance. The face may be heavily involved with erythema and crusting, particularly around the mouth. The neck and axilla are other characteristic sites (Figs 24.19 and 24.20). Adults may, rarely, be affected; see later.

Figure 24.19 Staphylococcal scalded skin syndrome. Very superficial peeling and erosions are seen about the mouth. Bright-red, tender skin is also typical.

Figure 24.20 Staphylococcal scalded skin syndrome. Very superficial erosions in the flexural areas of the neck and axillae are typical.

Differential diagnosis

The differential is that of losing sheets of skin. Forms of epidermolysis bullosa may need to be considered in very young children, and bullous fixed drug eruption may be considered, but the main differential is toxic epidermal necrolysis (TEN; see Fig. 24.21 and Ch.18). Staphylococcal scalded skin syndrome (SSSS) is more common in the child and starts typically around the mouth and face; in TEN, a causative drug would be expected.

Figure 24.21 Toxic epidermal necrolysis (TEN) in a child. Staphylococcal scalded skin syndrome must be distinguished from TEN, which can occur in children, although this is unusual. Note the widespread dusky rash and the skin peeling off the areas of friction on the trunk. (Courtesy of O. Dale Collins III, M.D., Ph.D.)

Treatment

Hospitalization, an antistaphylococcal antibiotic, and supportive measures should be given.

Staphylococcal scalded skin syndrome in adults

Staphylococcal scalded skin syndrome may, rarely, occur in adults secondary to infection of, for example, surgical wounds. Most cases occur in the context of either kidney failure (the toxin is renally excreted) or immunosuppression, but healthy adults can be affected. Blood cultures often are positive for Staph. aureus (whereas they are usually negative in children). Detection of the exfoliating toxin may be done with the newborn mouse bioassay. SSSS can be difficult to differentiate from TEN, but TEN often has mucosal involvement, whereas SSSS does not; pustules are more characteristic of SSSS, and a positive Nikolsky sign of uninvolved skin is more characteristic of SSSS. In cases where there is doubt, biopsy will demonstrate a different level of cleavage in the epidermis.

Toxic shock syndromes

Etiology and pathogenesis

The disease is typically caused by a toxin-producing Staph. aureus infection, classically of a superabsorbent tampon in a young woman during a menstrual period. Since superabsorbent tampons have been eliminated, the incidence of toxic shock syndrome (TSS) has decreased, but menstruating women still seem to be preferentially affected. Non-menstrual TSS may occur from Staph. aureus infection of wounds, catheters, contraceptive diaphragms, or nasal packing. The pathophysiology is believed to involve the secretion of an exotoxin, TSST-1, by Staph. aureus , which acts as a superantigen to cause the release of cytokines from a large number of both antigen-presenting cells and T-helper cells. This intense release of inflammatory mediators is probably responsible for the majority of systemic symptoms.

    A similar syndrome has been reported to occur from streptococcal infection (e.g. group A b -hemolytic or group B streptococcus) and is termed streptococcal toxic shock-like syndrome (STS-LS). In one patient, a novel toxin was isolated that was able to cause TSS in rabbits. The diagnosis of STS-LS should be suspected in a patient with hypotension and from whom group A streptococcus has been isolated. In addition, renal impairment, coagulopathy, liver involvement, adult respiratory distress syndrome, a generalized erythematous rash that may desquamate, and soft tissue necrosis, including necrotizing fasciitis, myositis, or gangrene may occur. Flu-like symptoms are common.

Clinical

The acute onset of high fever, vomiting, and watery diarrhea, sometimes with sore throat, headache, and myalgias is characteristic. Within 48 h, a diffuse, macular erythematous rash and non-purulent conjunctivitis, along with hypotensive shock, may ensue, accompanied by other systemic signs (e.g. disorientation, renal or hepatic dysfunction, headache, and myalgias). Swelling of the palms and soles, conjunctival hyperemia, a strawberry tongue, and desquamation of the palms and soles after 1–2 weeks also occur.

Differential diagnosis

This is the differential of diffuse acute erythema in an adult.

Treatment

Large volumes of fluid plus other vasopressors may be needed to maintain perfusion, usually given in the intensive care situation. Intravenous antistaphylococcal antibiotics, early vaginal irrigation, or drainage of the infected focus is necessary. The throat, blood, vagina, and urine should be cultured. If any abscess or tissue necrosis is present, immediate surgical debridement is indicated. Intravenous immunoglobulin infusion has been used, particularly for cases caused by Streptococcus.

Pitted keratolysis

Small 1–2-mm pits, reticulated or annular erosions, or extensive loss of the hyperkeratotic outer layer on the sole or toes in a teenager are characteristic (Figs 24.22–24.24). There is typically a history of prolonged wearing of footwear and of excessive sweating. The palms may rarely be affected, the lesions having the appearance of ringed collarettes. Causative bacteria include Kytococcus sedentarius , which can secrete a protease with callous-degrading activity.

    Erythromycin or clindamycin topically are effective. Aluminum chloride 20% helps reduce the hyperhidrosis and odor. Prolonged use of occlusive footwear should be avoided.

Figure 24.22 Pitted keratolysis. Multiple 1–2-mm pits in a teenager with prolonged wearing of footwear and sweating are typical.

Figure 24.23 Pitted keratolysis. Macerated skin on toe pulps, with annular patterning.

Figure 24.24 Pitted keratolysis. A rather more sharply defined lesion on the heel, a less common site, but showing the typical soggy appearance of the skin, resembling the changes seen after prolonged immersion in water.

Erythrasma

Erythrasma is caused by the bacterium Corynebacterium minutissimum . C. afermentans has also been reported. Red-brown patches, commonly of the groin or axilla, with a distinct border and little to no scale, occur in erythrasma (Fig.24.25). Wood's lamp examination showing coral-pink fluorescence is diagnostic (Fig.24.26); the fluorescence results from the production of porphyrins by the bacteria.

    Erythromycin topically or orally is effective. Topical clindamycin is an alternative. A single 1-g dose of clarithromycin has been reported to be effective. Some studies support the effectiveness of antimicrobial soaps against erythrasma, and these can be recommended to prevent recurrences.

Figure 24.25 (a,b) Erythrasma. Corynebacterium minutissimum is the bacterium responsible for this mild, chronic, superficial infection. Red-brown patches, commonly of the groin or axilla, with distinct border and little to no scale occur.

Figure 24.26 Corynebacterium minutissimum creates a water-soluble porphyrin that fluoresces coral pink under Wood’s light examination. This finding may be absent if the patient has bathed recently.

Trichomycosis axillaris

Trichomycosis represents a bacterial colonization of the hair. Corynebacterium tenuis is one of the bacteria identified in this situation. It is usually an incidental finding. Yellow, red, or black attachments on the hair, representing bacterial colonization, occur (Fig.24.27). Topical clindamycin twice a day, or simply shaving with subsequent regular washing, is effective.

Figure 24.27 (a,b) Trichomycosis axillaris. Yellow, red, or black attachments on the hair occur, representing bacterial colonization.

PRACTICE POINTS

Blistering distal dactylitis

Blistering distal dactylitis represents a bacterial infection of the pulp area of the distal digit. Group A b -hemolytic streptococcus is the usual culprit, but occasionally Staph. aureus may be found, alone or in combination with streptococci.

    A painful solitary or multiple blister or pustule on the volar fat pad of a child aged 2–16 years is characteristic of this condition (Figs 24.28 and 24.29). Adults may, rarely, be affected and, if so, are usually immunocompromised. Diagnosis is made by culture of the pus. Incision and drainage combined with oral antibiotics (e.g. dicloxacillin) is appropriate treatment.

Figure 24.28 Blistering distal dactylitis. This painful lesion should be drained, and the patient started on oral antibiotics. (Courtesy of Arlene Tsuchia, M.D.)

Figure 24.29 Blistering distal dactylitis.

Erysipeloid

Erysipeloid is a cutaneous infection by the gram-positive pleomorphic bacterium Erysipelothrix insidiosa . It mimics erysipelas (thus the name), but the patient lacks constitutional symptoms or lymphatic spread. The bacteria may be found on decaying meat, fish, or contaminated soil. Butchers, fishermen, farmers, or cooks are at highest risk. A presumptive diagnosis may be made given the classic history and clinical picture. If confirmation is needed, tissue culture using blood agar incubated at 35–37°C in 5–10% carbon dioxide is positive. Histopathologic examination, including Gram stain, does not usually show the organisms; however, electron microscopy will.

    A red, purplish, well-demarcated, urticarial plaque beginning on the hand, usually several days (usually 1–7) after inoculation while fishing, or other contact with dead fish or animals, is characteristic (Fig.24.30). Penicillin is the treatment of choice. Erythromycin and a cephalosporin are alternatives.

Figure 24.30 Erysipeloid affecting the thumb of a middle-aged woman. The source was presumed to be food prepared at home, as she had had no relevant occupational exposures. Infection may occur after minor penetrating injuries from fishbones or bone fragments from chickens or pigs.

Scarlet fever

Etiology and pathogenesis

The rash of scarlet fever is caused by a toxin-producing group A b -hemolytic streptococcus. The tonsil or pharynx is the usual site of infection, but surgical wounds or other foci are possible. A rapid antigen detection test may be performed, but this has a significant false positive rate, and negative tests should be backed up by culture. Early cases with a rash and fever need to be distinguished from Kawasaki disease.

Clinical

A child, typically 4–8 years of age, will develop a high fever, sore throat, headache, and vomiting. The exanthem follows within 1–2 days and appears as many small papules on diffuse erythema (Fig.24.31). The skin may feel rough, like sandpaper. Linear petechiae in the axillae and groin, Pastia lines, are classic, as is circumoral pallor. Desquamation, worse on the hands and feet, begins 7–10 days later (Fig.24.32). The tongue may be initially white and later red (strawberry tongue).

Figure 24.31 Scarlet fever. The rash of scarlet fever is usually generalized, often with small, papular lesions like sandpaper. There may be accentuation in the folds, frequently with linear purpura (Pastia lines).

Figure 24.32 Scarlet fever. Between 7 and 10 days after the onset of the rash, the skin often desquamates, particularly on the hands and feet.

Differential diagnosis

The differential of scarlet fever is that of a diffuse red rash in a child and is huge, but includes the following.

Treatment

Penicillin orally or intramuscularly is effective. Erythromycin may be used in penicillin-allergic patients. Recurrent attacks of scarlet fever may occur.

Acute paronychia

See Chapter 29.

Kawasaki disease

Etiology and pathogenesis

Kawasaki disease, also known as mucocutaneous lymph node syndrome, is currently the leading cause of pediatric acquired heart disease. It occurs most commonly in Japan , followed by other Asian countries. It mainly affects children aged less than age 5 years.

    Although, at the time of writing, the cause of Kawasaki disease is unclear, it has been included in this section on bacterial diseases as the pathogenesis is thought to represent a superantigen response to an infectious agent, possibly an unidentified respiratory agent with tropism for vascular tissue.

Clinical

The diagnosis is made in the setting of a fever for 5 days or more without obvious cause, and four of the five criteria listed in Table 24.4 (and illustrated in Figs 24.33 and 24.34).

    Between 20 and 25% of untreated patients develop significant cardiovascular complications, including arrhythmias (acute), aneurysms and thrombi (subacute), or scarring and ischemic heart disease (late). Generalized pustules with a resemblance to pustular psoriasis have been reported. Peripheral gangrene may occur. Adult cases of Kawasaki syndrome have been reported.

Figure 24.33 Kawasaki disease. A non-purulent conjunctivitis is classic. (Courtesy of O. Dale Collins, M.D.)

Figure 24.34 (a,b) Kawasaki disease. Note the swollen, inflamed, crusted lips. (Courtesy of O. Dale Collins, M.D.)

Figure 24.31 Scarlet fever. The rash of scarlet fever is usually generalized, often with small, papular lesions like sandpaper. There may be accentuation in the folds, frequently with linear purpura (Pastia lines).

Figure 24.32 Scarlet fever. Between 7 and 10 days after the onset of the rash, the skin often desquamates, particularly on the hands and feet.

Differential diagnosis

See differential for scarlet fever, discussed earlier.

Treatment

Hospital admission, high-dose aspirin (e.g. 80–100mg/kg per day in four divided doses, reduced to 3–5mg/kg as a single daily dose on day 10), and intravenous gamma-globulin (e.g. 2g/kg infused over 10h) are recommended. The treatment need not be withheld until the fifth day of fever if the diagnosis is reasonably certain. The patient's cardiac status should be closely monitored, including the use of echocardiograms.

Plasma exchange has been used in a child resistant to standard treatment, as has pulsed methylprednisolone.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.