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Common Bacterial Culprits
- Staphylococcal organisms and B hemolytic streptococci are common skin disease-causing bacteria.
Contributing Factors
- Immune deficiency states, use of steroid preparations (topical or systemic), and mechanical skin disruption can contribute to bacterial skin infections.
Types of Infections
- Infections can be primary or secondary:
- Primary infections arise on previously normal skin.
- Secondary infections arise on already diseased skin.
Primary Infections
- Direct skin and adjacent tissue infection
- Impetigo
- Ecthyma
- Folliculitis
- Furunculosis
- Carbuncle
- Sycosis
- Occasionally found in cellulitis cases
Secondary Infections
- Can occur in conditions like eczema, infestations, ulcers, etc.
- Cutaneous Diseases from Bacterial Toxins
- Staphylococcal scalded skin syndrome
- Toxic shock syndrome
Impetigo is a common skin infection with two classic forms: non-bullous and bullous.
Non-Bullous Impetigo
Non-bullous impetigo constitutes over 70% of cases. It typically starts on traumatized skin of the face or extremities.
The most common precursor lesions for non-bullous impetigo include insect bites, abrasions, lacerations, chickenpox, scabies, pediculosis, and burns.
Initially, a tiny vesicle or pustule forms, which quickly develops into a honey-colored crusted plaque, usually under 2 cm in diameter.
The infection can spread to other body parts through fingers, clothing, and towels. Lesions usually cause minimal pain or surrounding redness, and there are typically no constitutional symptoms.
Occasional pruritus (itching) occurs, and regional adenopathy (enlarged lymph nodes) is present in about 90% of cases. Leukocytosis (increased white blood cell count) is seen in around 50% of patients.
Untreated cases often resolve without scarring within about 2 weeks.
Differential Diagnosis of Non-Bullous Impetigo
- Viral infections:
- Herpes simplex
- Varicella zoster
- Fungal infections:
- Tinea corporis
- Kerion
- Parasitic infections:
- Scabies
- Pediculosis capitis
- All of these infections have the potential to become impetiginized.
Causative Organisms
- Staphylococcus aureus is the predominant organism responsible for non-bullous impetigo.
- Group A beta-hemolytic streptococci (GABHS) are also implicated in the development of some lesions.
Bullous Impetigo
Bullous impetigo is primarily seen in infants and young children. It is exclusively caused by coagulase-positive Staphylococcus aureus, with around 80% being attributed to phage group 2.
Characteristics of Bullous Impetigo
- Flaccid, transparent bullae tend to develop most commonly on the skin of the:
- Face
- Buttocks
- Trunk
- Perineum
- Extremities
- Neonatal bullous impetigo can initiate in the diaper area.
- Rupture of bullae occurs easily, resulting in a narrow rim of scale at the edge of a shallow, moist erosion.
- Surrounding redness (erythema) and regional adenopathy (enlarged lymph nodes) are typically absent.
- Unlike non-bullous impetigo lesions, those of bullous impetigo are a manifestation of localized staphylococcal scalded skin syndrome and develop on intact skin.
Diagnosis
Diagnosing bacterial skin infections involves the following considerations:
Cultures for Identification
Cultures of fluid from an intact blister or moist plaque should be obtained to identify the causative agent.
Additional Testing
If the patient appears ill, blood cultures should also be obtained to assess the presence of systemic infection.
- Septic arthritis
- Osteomyelitis
- Septicemia
- Pneumonia
- Acute glomerulonephritis, particularly associated with M groups 2, 49, 53, 55, 56, 57, and 60.
Treatment
- Erythromycin (30-50mg/Kg/24 hr divided three to four times daily for 7–10 days)
- Amoxicillin clavulanate
- Staining with Gentian Violet
Staphylococcal scalded skin syndrome is primarily observed in infants and children under 5 years old. It encompasses a spectrum of disease, ranging from localized bullous impetigo to generalized cutaneous involvement accompanied by systemic illness.
Characteristics of Staphylococcal Scalded Skin Syndrome
- The rash's onset might be preceded by malaise, fever, irritability, and extreme skin tenderness.
- Erythema develops diffusely and is more pronounced in flexural and periorificial areas.
- Inflammation of the conjunctivas occasionally leads to purulence.
- The skin, initially brightly erythematous, can quickly adopt a wrinkled appearance. In severe cases, sterile, flaccid blisters and erosions form diffusely.
- Circumoral erythema is distinct, along with radial crusting and fissuring around the eyes, mouth, and nose.
- Epidermis may separate with gentle shear force (Nikolsky sign). Larger sheets of epidermis can peel away, revealing moist, glistening, denuded areas.
- Secondary cutaneous infections, sepsis, and fluid and electrolyte imbalances can result from this.
- The desquamative phase initiates after 2-5 days of cutaneous erythema; healing occurs without scarring within 10-14 days.
- Patients might exhibit pharyngitis, conjunctivitis, and superficial erosions of the lips, but intraoral mucosal surfaces are typically unaffected.
- While some patients may appear unwell, many are relatively comfortable aside from the pronounced skin tenderness.
Differentials
- Bullous impetigo
- Epidermolysis bullosa
- Epidermolytic hyperkeratosis
- Pemphigus
- Drug eruption
- Erythema multiforme
- Drug-induced toxic epidermal necrolysis
Causative Factors of Staphylococcal Scalded Skin Syndrome
Staphylococcal scalded skin syndrome is predominantly caused by phage group 2 staphylococci, especially strains 71 and 55. These strains are localized at sites of infection.
Foci of infection can include the nasopharynx, and less commonly, the umbilicus, urinary tract, superficial abrasions, conjunctivae, and blood.
The epidermolytic toxins A and B are responsible for the pathology associated with this syndrome.
Ecthyma is characterized by pyogenic skin infection where adherent crusts form over underlying ulceration.
Predisposing Factors
Poor hygiene and malnutrition are predisposing factors. The disease is caused by the same organisms responsible for impetigo.
Characteristics of Lesions
Lesions initially appear as small bullae or pustules on an erythematous base, which progressively increase in size.
Crust and Healing
The resulting crust is typically difficult to remove, and the lesion ultimately heals with scarring.
Commonly Affected Sites
The buttocks, thighs, and legs are the most commonly affected sites.
Furuncles
Furuncles are caused by the invasion of hair follicles by pyogenic staphylococci. Lesions are usually perifollicular and begin as small, painful, hard lumps with a bright red surface. They eventually become pointed, break down, and discharge pus. Furuncles heal with scarring and do not occur on non-hairy surfaces like palms, soles, or mucous membranes.
Carbuncles
Carbuncles are an aggregation of furuncles. They typically form deeper and more extensive lesions.
Folliculitis
Folliculitis involves multiple small pustular lesions found on hair follicles, often affecting areas like the beard and thighs. It may result from the irritant effect of twisted hair shafts digging into the skin. For example, folliculitis in the beard area of men is known as sycosis barbae.
Management
- Swabs for Bacterial Culture
- Acute Staphylococcal Infections
- Chronic and Recurrent Cases
- General Measures
- Carbuncles
- Complications
Swabs for bacterial culture are taken from the lesion and from carrier sites such as the nose, axilla, and groin. Obesity, diabetes mellitus, and occlusion from clothing are predisposing factors.
Acute staphylococcal infections are treated with antibiotics, both systemic (e.g., flucloxacillin or erythromycin) and topical (e.g., fusidic acid, mupirocin, or neomycin).
Chronic and recurrent cases are more challenging. Carrier sites, like the nose, require treatment with a topical antibiotic (e.g., mupirocin).
General measures include improved hygiene, regular bathing or showering, and the use of antiseptics in the bath and on the skin (e.g., chlorhexidine). Courses of oral antibiotics might be necessary.
Carbuncles often require prompt surgical drainage.
An infrequent complication is thrombosis in the cavernous sinus, associated with facial infection.
Practice Questions
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