Skin and Soft Tissue Infections

What are the three layers of the skin?

Epidermis (Barrier)

Dermis (Nerve+Vessel innervations)

Hypodermis (SUBQ Fat)

What is the epidermis?

Outer layer of the skin, acts as a physical barrier. A portal of entry for microbes occurs when the epidermis is broken

What is the dermis?

Inner layer of the skin, consists of blood vessels, nerves, hair follicles, and glands, all of which can serve as portal of entry for microbes

Why can only certain microbes live on the skin as normal flora?

The skin is inhospitable for many microbes because it is covered in salt, sweat, and sebum which possess antimicrobial properties, and the skin is continuously sloughed off

Most of the normal skin flora consists of gram positives and yeasts

What microbes constitutes as part of the normal flora of the skin?

Gram positive bacteria (mostly staphylococcus epidermis)

Yeasts

Which areas of the skin consist of the most diverse normal flora?

Warm moist areas of the skin (under the arms, between the legs, perineal region)

Can consist of species such as staphylococcus aureus, Gram negative bacteria, and GI normal gut flora

What is a benefit and risk of the skin normal flora?

Benefit - Acts as microbial antagonism against parasitic organisms

Risk - Can become parasitic if it enters openings in the skin barrier

What bacterial strain is coagulase negative staph?

Staphylococcus epidermis (skin normal flora)

What bacterial strain is coagulase positive staph?

Staphylococcus aureus ("infectious" staph)

What are skin rashes?

A change in the color or texture of skin. Associated with an active infection if it is accompanied with systemic symptoms or there are signs of a deep rash

What is an exanthem skin rash?

A rash on the skin accompanied by systemic symptoms

What is an enanthem skin rash?

A rash on the mucous membranes accompanied by systemic symptoms

What are common causes of rashes?

-Allergic response

-Drug reaction

-Autoimmune response

-Bacterial toxin induced

-Pathogen damage

-Immune response to pathogen

What are categories of skin rashes that are less than 1cm in size?

Macule

Vesicle

Papule

Pustule

What are categories of skin rashes that are greater than 1cm in size?

Patch

Plaque

Bullae

Nodule

Wheal

What is a macule?

A flat rash less than 1cm in size with no induration or texture (non papable). Often the starting appearance of a skin infection

What types of skin rashes are characterized by being non palpable

Macule (<1cm in size)

Patch (>1cm in size)

What is a vesicle?

A palpable rash less than 1cm in size with induration. It is caused by an accumulation of clear fluid in the epidermis, making it fragile

What types of skin rashes are characterized by accumulation of clear fluid and fragility?

Vesicle (<1cm in size)

Bullae (>1cm in size)

What is a papule?

A palpable rash less than 1cm in size that is caused by an accumulation of "material" other than fluid (ex:infection). Feels solid upon palpitation

What types of skin rashes are characterized by an accumulation of material + feeling "solid" on palpitation?

Papule (<1cm in size)

Plaque (>1cm in size)

What is a pustule?

A palpable rash less than 1cm in size that is characterized by an accumulation of pus from dead inflammatory cells

What type of skin rash is characterized by an accumulation of pus?

Pustule

What is a patch?

A nonpalpable skin rash greater than 1cm in size that is flat with no induration and texture

A larger form of a macule

What is a plaque?

A palpable skin rash greater than 1cm in size that is characterized by an accumulation of "solid" material (ex: infection).

A larger form of a papule

What is a bullae?

A palpable skin rash greater than 1cm in size tat is characterized by an accumulation of clear fluid

A larger form of a vesicle

What is a nodule?

A palpable skin rash greater than 1cm in size that is formed in the dermis or SUBQ fat (hypodermis)

What is a wheal?

A palpable skin rash that is transient and characterized by peripheral redness and central pallor.

It is the result of histamine release and is often associated with allergic reactions

Which type of skin rash is associated with allergic reactions?

Wheal

Which type of skin rash is associated with deeper layers of the skin?

Nodule

What is a skin ulcer?

An open sore of the skin that is maintained (slow healing) by inflammation, infection, or medical conditions that impede healing (diabetes) - often penetrating deep into the skin

What are culturing techniques for skin and soft tissue infections?

Skin scraping (Fungal Infections)

Aspiration (Fluid)

Tissue biopsy (Straw needle apparatus)

Swabs (Leading edge or deep to collect pathogen)

How should swabbing be done when collecting cultures from skin and soft tissue infections?

Swab the leading edge or deep into the infection to collect the suspected pathogen (and avoid normal flora)

What are the two most common bacterial strains responsible for skin infections?

Staphylococcus aureus

Group A streptococcus

What are pathogenic factors of staphylococcus aureus?

Gram positive cocci

Catalase positive (aerobic)

Coagulase positive (able to form clots)

Staphylokinase (dissolve clots)

Slime Layer (evasion)

Protein A on Cell Wall (evasion)

Cytolytic toxins (cell damage)

Leukocidin toxins (wbc damage)

Exofoliative toxins (skin decoupling)

Epidermal cell differentiation inhibitor (penetration)

Toxic shock syndrome toxin (superantigens)

What are pathogenic factors of group A streptococcus?

Gram positive cocci

Catalase negative (facul anerobic)

M proteins (attachment and evasion)

Streptokinase (dissolve clots)

Hyaluronidase (gaps between tissues)

Deoxyribonucleases (breaks down DNA)

Streptolysin (hemolytic)

Pyrogenic toxins (Skin redness + warmth)

Exotoxin A (superantigen)

What are differences between staphylococcus aureus and staphylococcus epidermis?

Staphylococcus aureus

-Possesses coagulase and staphylokinase (able to form and dissolve clots to evade defenses)

-Possess protein A on cell wall (evade defenses)

-Produces many exotoxins (cytolytic factors, leukocidin, epidermal cell differentiation inhibitor, exfoliative toxins, toxic shock syndrome toxin

-Most common cause of skin and soft tissue infections

What layer of the skin does folliculitis affect?

Causes inflammation to epidermis, dermis, and in severe cases the hypodermis (Furuncle and carbuncle formation)

What causes folliculitis?

Caused by localized bacterial infection of the hair follicles

Which pathogens are responsible for folliculitis?

Staph aureus!

Pseudomonas aeruginosa

What are symptoms of folliculitis?

Localized inflammation

Redness

Pain

Swelling/edema

What are key indicators that a patient has folliculitis compared to other skin and soft tissue infections?

Inflammation is localized to the affected hair follicle and is commonly found in the back of the neck

If the inflammation progresses to furuncles, the nodule often forms a yellow/white tip (like a pimple) that ruptures on its own

What is the treatment for folliculitis?

-Normal-

Warm compress (open+clean pores) + antibacterial soap (kill off causative bacterial pathogen)

-Multiple lesions-

Topical antibiotics (Mupirocin/Clindamycin)

-Severe lesions-

Oral antibiotics

What are furuncles?

Aka boils

Advanced folliculitis in which the inflammation has spread from the follicle to the surrounding dermis and hypodermis, causing increased pain and forming a nodule (hypodermis invol)

The furuncle progresses tot he point in which it develops a yellow/white tip that eventually ruptures and drains - ending the inflammation

What are carbuncles?

Furuncles (folliculitis) that take longer to heal often due to patients with increased skin thickness (older men), which results in increased inflammation + pressure on the hypodermis, and can eventually cause systemic involvement, toxic shock (superantigen production) and damage to the hypodermis (necrotizing fasciitis)

What is the treatment for furuncles and carbuncles?

Applying warm compress to cause spontaneous rupturing of the furuncle

Incision and drainage of the furuncle/carbuncle

Oral antibiotics if signs of systemic involvement are present

Who is most vulnerable to folliculitis?

Older men - possess thick skin which makes it harder for furuncles to erupt, resulting in more carbuncles

Which layer of the skin does stapylococcal scalded skin syndrome affect?

Epidermis

What is staphylococcal scalded skin syndrome?

A skin infection characterized by decoupling and sloughing off of skin starting from near the mouth and eventually spreading throughout the body, thus appearing as if the patient has been scalded/burnt

What pathogen is responsible for staphylococcal scalded skin syndrome?

Staphylococcus aureus strains which produce exfoliative exotoxins

What causes staphylococcal scalded skin syndrome?

Certain staphylococcus aureus strains produce exfoliative exotoxins, which causes the epidermis to decouple from surrounding and underlying tissue, resulting in the skin being sloughed off.

The exotoxin spreads through the bloodstream and causes skin to slough off throughout the whole body

What are symptoms of staphylococcal scalded skin syndrome?

Sloughing off of skin

Redness and wrinkling of skin (mouth -> body)

Vesicle blisters

Crusting of skin after vesicles rupture

What are key indicators that a patient with a skin and soft tissue infection has staphylococcal scalded skin syndrome?

Exfoliation/sloughing off of skin starting from mouth and spreading throughout the body

What is the treatment of staphylococcal scalded skin syndrome?

IV antibiotics or vancomycin for (MRSA resistant strains)

What is the action of exfoliative toxins?

Exfoliative toxins causes decoupling of skin from surrounding and underlying tissue, which results in the skin being sloughed off in staphylococcal scalded skin syndrome

What layer of skin does impetigo affect?

The epidermis

What is impetigo?

A skin infection characterized by pleomorphic lesions located between the nose and mouth.

What causes impetigo?

Damage to the skin between the nose and mouth (often through using rough objects to wipe the nose) allows bacterial pathogens (staphy aureus and strepto pyogens) to enter. These bacterial species causes inflammation characterized by pleomorphic lesions

What are symptoms of impetigo?

Pleomorphic lesions (Patches, Vesicles, Pustules)

Crusting of old pustules near nose and mouth

What are key indicators that a patient with a soft and skin tissue infection has impetigo?

Lesions appearing between the nose and mouth in children

What pathogens cause impetigo?

Staphylococcus (Predominant)

Streptococcus pyogenes

What is the treatment of impetigo?

Limited - Topical antibiotics (Mupirocin)

Severe - Oral antibiotics (Cloxacillin)

Which populations are vulernable to impetigo?

Children in the summer

What layer of the skin does erysipelas affect?

Dermis

What is erysipelas?

A deep skin infection characterized by well demarcated butterfly indurated lesions on the face, arms and legs

What causes erysipelas?

Streptococcus pyogenes enters through a portal of entry, most commonly through breaks of the skin barrier, and releases pyrogenic toxins, which causes erythema on the face, arms and legs

What pathogen is responsible for erysipelas?

Streptococcus pyogenes

Which populations are vulnerable to erysipelas?

Extremes of age

Previous impetigo/streptococcal pharyngitis (GAS infections)

What are symptoms of erysipelas?

Indurated well demarcated skin redness

Pain

"Butterfly wing lesions" on the face

Systemic symptoms (fever, chills)

Rx for bacteremia

What are key indicators that a patient has erysipelas compared to other skin and soft tissue infections?

Lesion is indurated and well demarcated

"Butterfly wing lesion" apperance on the face

What is the treatment of erysipeleas?

Oral or IV antibiotics (Penicillin/amoxicillin - B lactams)

What layer of the skin does cellulitis affect?

Hypodermis

What is cellulitis?

Acute skin infection that involves the hypodermis most commonly in the lower extremities

Which populations are vulnerable to cellulitis?

Middle aged and older adults

Immunocompromised

Diabetes

Obesity

Chronic venous stasis (immobility)

Previous cellulitis

What pathogens cause cellulitis?

Staphylococcus aureus

Streptococcus pyogenes

What causes cellulitis?

Bacterial pathogens enter the skin through breaks in the skin barrier and spread to the hypodermis, causing an infection and increased risk of bacteremia and sepsis due to involvement of the blood vessels in the hypodermis

What are symptoms of cellulitis?

Poorly demarcated area of redness and swelling in the lower extremities (can last up to 48-72 hours of initiating treatment)

Pain

Systemic symptoms (Fever, chills)

What is necrotizing faciitis?

Acute skin infection characterized by death of tissue in the deep fascia and hypodermis, resulting in immense pain (later numbness) and rapid progression

What layer of the skin does necrotizing faciitis affect?

Hypodermis and deep fascia

What are type 1 necrotizing infections?

Infection caused by a mix of bacterial pathogens other than GAS, most commonly in postoperative and previously ill patients

What are type 2 necrotizing infections?

Infection caused by group A strep to staphylococcus aureus, commonly seen in the community setting in patients without known risk factors

What are symptoms of necrotizing faciitis?

-Rapidly progressing (cm per hr) bullae, crepitus, or necrosis which are not raised and notn demarcated

-Disproportionate pain

-Numbness in late stages of disease

-Hemodynamic instability

-Firmness of hypodermis

-Risk for sepsis (Fever, tachycardia, hypotension)

-Risk for streptococcal shock syndrome (superantigens)

What pathogens cause necrotizing faciitis? (Type 2)

Streptococcus pyogenes and Staphylococcus aureus

What are key indicators that a patient with a skin and soft tissue infection has necrotizing faciitis?

Rapidly progressing red skin lesions

Dusky purple skin indicative of tissue death

No demarcation or marked indurations

Disproportionate pain compared to observed tissue damage

Which populations are vulnerable to necrotizing faciitis?

Post surgical patients

History of recent trauma

Recent streptococcus pyogenes infection (streptococcal pharyngitis)

What is the treatment for necrotizing faciitis?

Skin biopsy for diagnosis

Broad spectrum antibiotics for type 1

IV beta lactam antibiotics for type 2 (GAS)

Clindamycin as an antitoxin

IV immunoglobin G for streptococcal toxic shock syndrome

Amputation

What is streptococcal toxic shock syndrome?

An uncontrolled immune response from a streptococcus pyogenes infection caused by the release of superantigens

What is the treatment for streptococcal toxic shock syndrome?

Clindamycin (antitoxin)

IV Immunoglobin G - reduces effects of toxin and modulates immune response

What is varicella?

aka chickenpox

Highly contagious viral skin infection characterized by pleomorphic rashes on the trunk, head, and extremities that can spread airborne, droplets, or direct contact

What pathogen causes varicella?

Varicella-zoster (a form of the human herpes virus)

What are the symptoms of varicella?

-Systemic symptoms-

Fever

Headache

Sore throat

Rhinitis

Abdominal pain

Pleomorphic rash (1-2 days after systemic symptoms)

Pruritus

What are key indicators that a patient with a skin and soft tissue infection has varicella?

Presence of pleomorphic rash all throughout the body

History of contact with varicella (highly contagious via airborne + droplet + contact)

What is the treatment for varicella?

Antihistamines (itchiness)

Daily baths/showers with careful drying

Covering affected area to reduce transmission

Prevent - routine varivax vaaccine at 15 months + 4-6 y/o

Which populations are vulnerable to varicella?

Unvaccinated children

What is herpes zoster?

A viral skin infection which is caused by the reactivation of a latent form of the varicella virus, often as a cause of stress, and causes symptoms that follow a dermatome pattern

What causes herpes zoster?

A latent form of the varicella virus which resides in the dorsal root or cranial nerve ganglia is activated as a result of age, immunosuppression, or stress. This causes the virus to infect the peripheral nerves and cause pain and pleomorphic lesions to a specific dermatome

What pathogen is responsible for herpes zoster?

Latent varicella zoster

What are the symptoms of herpes zoster?

-Prodromal/Systemic Manifestations-

Fever

Pruritus

Pain in single dermatome

Pleomorphic lesions in 1-2 adjacent thoracic dermatomes (after 3-4 days of prodromal manifestations

What are key indicators that a patient with a skin and soft tissue infection has herpes zoster?

Pain and pleomorphic lesions limited to 1-2 adjacent dermatomes, normally in the thoracic region

Which populations are vulnerable to Herpes Zoster?

Older patients

Patients w/o Varicella or shingrix vaccine

Immunocompromised patients

Stress