Lesson 13.2: Skin Infections and Infestations

Introduction

In this lesson, we will explore various skin infections and infestations that are critical for any healthcare professional to recognize and manage. By understanding the mechanisms of bacterial, viral, and fungal infections as well as skin infestations, you will enhance your ability to provide effective care to patients across various age groups.

Learning Objectives

1. Diagnose and manage bacterial, viral, and fungal skin infections.
2. Recognize cellulitis, abscess, and necrotizing infection.
3. Address infestations and their treatment.
4. Select antimicrobial therapy for common skin infections.
5. Recognize necrotizing soft-tissue infection requiring urgent care.

Bacterial Skin Infections

Overview

Bacterial infections of the skin are among the most common dermatologic conditions. The two most typical bacteria responsible for these infections are Staphylococcus aureus and Streptococcus pyogenes. These infections can vary in severity and may require different approaches for diagnosis and treatment.

Common Bacterial Infections

1. Impetigo

Impetigo is a highly contagious skin infection, primarily caused by Staphylococcus aureus or Streptococcus pyogenes. It often presents during hot and humid months, particularly among children.

Characteristics:

• Red sores around the nose and mouth.
• The sores burst and develop honey-colored crusts.

Treatment:

• Topical antibiotics such as mupirocin or fusidic acid.
• If widespread, systemic antibiotics such as cephalexin may be necessary.

Example:

Consider a 5-year-old patient with a scabbed area around the mouth. Upon examination, the area shows several red, honey-crusted lesions. A diagnosis of impetigo is made, and topical mupirocin is applied.

2. Cellulitis

Cellulitis is an infection of the deeper layers of the skin, often caused by Streptococcus or Staphylococcus. It typically arises from a break in the skin.

Characteristics:

• Redness and swelling of the area.
• Warmth and tenderness to touch.
• Fever may be present.

Treatment:

• Initial treatment with oral antibiotics such as dicloxacillin or cephalexin.
• Increased severity may require intravenous antibiotics.

Example:

A 30-year-old patient presents with a red swollen leg after a bug bite. An examination reveals significant warmth and tenderness in the area. After diagnosing cellulitis, the patient is started on oral cephalexin.

3. Necrotizing Fasciitis

This severe, rapidly progressing infection affects the fascial plane and subcutaneous tissue, and it requires immediate surgical intervention.

Characteristics:

• Severe pain out of proportion to examination findings.
• Rapid swelling and systemic symptoms such as fever.

Treatment:

• Urgent surgical debridement.
• Broad-spectrum intravenous antibiotics.

Example:

A patient complains of increasing pain and swelling in the leg after a minor injury. Examination reveals exquisite tenderness, and blood tests show elevated white blood cell counts. Surgical consultation is initiated for suspected necrotizing fasciitis.

Viral Skin Infections

Overview

Viral infections of the skin, such as herpes simplex and varicella zoster, play a significant role in dermatology. These infections can lead to significant morbidity if not properly managed.

Common Viral Infections

1. Herpes Simplex Virus (HSV)

HSV is classified primarily into two types: HSV-1 (often oral) and HSV-2 (usually genital).

Characteristics:

• Painful vesicular lesions at the site of infection.
• Often accompanied by systemic symptoms like fever.

Treatment:

• Antiviral medications like acyclovir or valacyclovir.

Example:

A patient presents with blisters around the lips and an accompanying fever. The diagnosis of herpes labialis is made, and the patient is started on acyclovir.

2. Varicella Zoster Virus (VZV)

This virus causes chickenpox in children and can reactivate later in life as shingles.

Characteristics:

• Pruritic vesicular rash that crusts over.
• Shingles presents as a painful dermatomal rash.

Treatment:

• Supportive care for chickenpox, antivirals like acyclovir for shingles if initiated early.

Example:

A 10-year-old child with a recent rash and fever is diagnosed with chickenpox after examination reveals vesicular lesions on the trunk. Supportive care is advised.

Fungal Skin Infections

Overview

Fungal infections are prevalent and can affect anyone. They tend to thrive in warm, moist environments.

Common Fungal Infections

1. Tinea (Ringworm)

Tinea infections are caused by dermatophyte fungi and often present in various forms depending on the body part affected (e.g., tinea corporis, tinea capitis).

Characteristics:

• Circular, red, itchy patches with clear centers.

Treatment:

• Topical antifungals like clotrimazole or terbinafine for localized infections.
• Oral antifungals like griseofulvin for widespread infections like tinea capitis.

Example:

A 12-year-old presents with circular lesions on the scalp. After examining the lesions, a diagnosis of tinea capitis is made, and griseofulvin is prescribed.

2. Candidiasis

Typically caused by the Candida species, this infection is common in warm, moist areas such as the groin and under breasts.

Characteristics:

• Red, itchy rash with a well-defined border and sometimes small pustules.

Treatment:

• Topical antifungal cream (e.g., nystatin) for localized infections.
• Systemic antifungal for severe cases.

Example:

An adult female presents with pruritic lesions in the folds of her arm. A diagnosis of candidiasis is made, and nystatin cream is recommended.

Infestations

Overview

Infestations by ectoparasites can lead to itchy and sometimes severe dermatitis. Common infestations include scabies and lice.

Common Infestations

1. Scabies

Scabies is caused by the Sarcoptes scabiei mite, which burrows into the skin.

Characteristics:

• Intense itching, especially at night.
• Burrows visible as small, linear tracks on the skin.

Treatment:

• Permethrin cream or oral ivermectin for severe cases.

Example:

A 25-year-old presents with intense itching and burrows in the web spaces of the fingers. After diagnosing scabies, permethrin cream is applied to the entire body.

2. Lice

Pediculosis can occur in various forms, but head lice are most common.

Characteristics:

• Itching of the scalp.
• Visible nits (eggs) attached to hair.

Treatment:

• Permethrin lotion or pyrethrin shampoo applied as directed.

Example:

A 7-year-old child presents with excessive scratching of the scalp. Upon examination, multiple nits are identified, and treatment with permethrin is initiated.

Conclusion

In summary, understanding skin infections and infestations is crucial for proper diagnosis and treatment. This lesson covered bacterial, viral, and fungal infections, along with infestations, offering insights into their presentations and management. Recognizing the signs and symptoms can lead to earlier interventions and better patient outcomes.

Study Notes

• Bacterial skin infections include impetigo, cellulitis, and necrotizing fasciitis.
• Treatment for bacterial infections often includes antibiotics based on culture sensitivity.
• Viral infections like herpes simplex and VZV require antiviral medications.
• Fungal infections, such as tinea and candidiasis, are treated with antifungal therapies.
• Infestations such as scabies and lice require topical or systemic prescriptions for eradication.