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

myositis

Infection of skeletal muscle tissue, often secondary to trauma or bacteria

Main Pathogens: staphylococcus aureus, clostridium

Forms:

• Pyomyositis

• gas gangrene

Symptoms: muscle pain, swelling, fever, tenderness, crepitus

Diagnosis: imaging

Treatment: IV antibiotics (vancomycin, piperacillin-tazobactam), surgical drainage

Surgical Wound Infection

Infection at surgical incision site, VERY common hospital-acquired infection

Main Pathogens

• Staphylococcus aureus (MRSA)

• staphylococcus epidermis

• gram - bacteria

Prevention:

• aseptic technique, skin disinfection, proper postoperative care

Pressure and Vascular Ulcer Infections

Chronic skin breakdown in immobile or vascular-compromised patients

Pathogens: polymicrobial—enterococcus, pseudomonas, and anaerobes

Management: debridement, pressure-relief, antibiotics

Prevention: repositioning, nutrition, daily wound assessment

Superficial Mycoses

Fungal skin infection affects outer epidermis

Cutaneous Mycoses

fungal skin infection that affects hair, nails, stratum, and corneum

Subcutaneous Mycoses

fungal skin infection that affects deeper tissue (traumatic inoculation)

Opportunistic Fungi

Fungal skin infection that affects immunocompromised people

Candida Infections

Part of normal microbiota in skin, gut, mouth, and vagina

Most common species: candida albicans

Main infections:

• cutaneous candidiasis: rash in skin folds, under breasts

• oral thrush: white plaque on tongue

• Paronychia: nail fold inflammation

• vaginal candidiasis: itching, discharge

Treatment: oral/ topical antifungals

Malassezia Infection

Lipophilic yeast

Diseases:

• Pityriasis versicolor: hypo/hyper pigmented patches

• Seborrheic Dermatitis: scalp, face

• Catheter-related infections

Treatment: topical antifungals

Herpes Simplex Virus

DNA Virus - Herpesviridae family

HSV-1: oral infections, “cold sores”

HSV-2: genital infections

Varicella-Zoster Virus

Herpesviridae Family

Primary Infection: varicella (chickenpox)

Recativation: herpes zoster (shingles)

Treatment: vaccine, antibiotics, pain control

Human Papillomavirus (HPV)

DNA Virus - papillomaviridae family

infects keratinocytes —> benign or malignant grows

HPV-16 and HPV-18: cervical cancer

Prevention: Vaccine

Common Lesions:

• verruca vulgaris: common wart

• plantar warts: soles of feet

• anogenital warts: sexual transmission

Molluscum Contagiosum (Poxvirus)

DNA Virus - poxviridae family

Lesions: small, dome-shaped bumps

Common: immunosuppressed adults, children

Keratitis

Corneal Infection

inflammation/ infection of the cornea —> vision threatening

Main Causes:

• infected contact lenses

• HSV-1

Herpes Zoster Ophthalmicus (HZO)

reactivation of Varicella-Zoster virus in the ophthalmic branch of the trigeminal nerve.

Endophthalmitis - severe intraocular infection

Infection inside the eye (aqueous + vitreous humors).

Types:

• Exogenous: after surgery, trauma, or corneal perforation.

• Endogenous: from bloodstream (sepsis, endocarditis, etc.)

Symptoms: Sudden severe eye pain. Vision loss (rapid). Redness, eyelid swelling.

Hypopyon (pus in anterior chamber).

Treatment:

• Intravitreal antibiotics immediately.

• Vitrectomy in severe cases.

• Hospitalization and systemic antibiotics.