Skin and Ocular Infectious Diseases

epidermis

outer layer of the skin (keratinized)

dermis

middle layer of skin (connective tissue, glands, follicles)

subcutaneous tissue

deepest layer of skin (fat, vessels, nerves)

Exogenous 

*route of infection

from outside (cuts, trauma, bites)

endogenous

*route of infection

from normal microbiota

staphylococcus aureus

• Gram-positive cocci

• catalase+, coaglualse +

• diseases: folliculitis, impetigo, abscesses

staphylococcus epidermis

• gram-positive cocci

• catalase +, coagulase -

• forms biofilms

• causes chronic device-associated infections

streptococcus pyogenes

• gram positive cocci in chains

• catalase -, β-hemolytic

• Diseases: impetigo, erysipelas, cellulitis, “flesh eating disease”

pseudomonas aeruginosa

• gram-negative rod

• oxidase +

• found in water, soil, moist environments

• typical infections: folliculitis, “simmers ear”, burn wounds

otitis externa “swimmers ear”

Anatomy: skin-lined canal → similar to other skin infections

Main pathogens:

• Pseudomonas aeruginosa (most common)

• Staphylococcus aureus

• Candida spp., Aspergillus spp. (fungal otitis)

Clinical: pain, itching, redness, swelling, discharge

Treatment: cleaning + topical antibiotics (ciprofloxacin) ± antifungals

folliculitis

Inflammation/infection of the

hair follicle.

Main pathogen:

• Staphylococcus aureus

Common sites: beard, scalp, chest,

thighs

Predisposing factors: shaving, friction,

occlusion, sweat

Treatment: hygiene + topical antibiotics

(mupirocin, clindamycin)

furuncle and carbuncle

Furuncle (boil): deep infection of hair follicle →

abscess

Carbuncle: cluster of interconnected furuncles

Main pathogen:

• Staphylococcus aureus

Clinical: painful, red, fluctuant nodules with pus

Treatment: incision & drainage ± antibiotics (MRSA

coverage if needed)

Impetigo

Etiology:

• Staphylococcus areas (most common)

• streptococcus pyogenes

Clinical features:

• honey-colored crust around the nose and mouth

• blisters

Diagnosis:

• swab from active lesion

treatment:

• topical mupirocin

• oral cephalexin, dicloxacillin, clindamycin

*common in children, spreads by contact/ scratching, and is very contagious

erysipelas

Infection of the dermic and lymphatic blood vessels

Etiology:

• streptococcus pyogenes

Clinical features:

• bright red, swollen, hot skin with raised borders

Diagnosis

• swab from legion edge if open

cellulitis

Etiology:

• Staphylococcus areas

• streptococcus pyogenes

• sometimes both

• entry via. skin trauma, ulcers, surgical wounds

clinical features

• redness, swelling, pain, heat, tenderness

• poorly defined borders

diagnosis:

• clinical evaluation

treatments

• antibiotics

necrotizing fasciitis

infection of the fascia and deep subcutaneous tissue, often producing gas and necrosis

Pathogens:

• streptococcus pyogenes

• clostridium perfringens

clinical features:

• severe pain

• rapid swelling and skin discoloration (purple)

• necrosis, blisters and crepitus (gas under skin)

diagnosis:

• clinical suspicion with CT scan and tissue culture

treatment:

• emergency surgery

• IV broad-spectrum antibiotics