Bacterial Skin Infections Flashcards
3 major factors for development of bacterial infection
(1) the portal of entry and skin barrier function
(2) the host defenses and inflammatory response to microbial invasion,
(3) the pathogenic properties of the organism
Primary infection
- Invasion of normal skin by usually a single speciesbacteria.
- Treatment of bacterial pathogen, cures the lesion
- Ex: Impetigo, erysipelas, furunculosis
Secondary infection
- Develop in areas of already damaged skin
- Bacteria present did not produce underlying skin disorder but may aggravate and prolong the disease
- Usually mixture of organisms
- Ex: Atopic dermatitis with secondary infection
What are the major pathogens of bacterial skin infections?
S. aureus or group A Streptococcus
Define impetigo
- Common, highly contagious
- Superficial skin infection (Pyoderma)
- Bullous or non-bullous: non-bullous is majority**
- Seen in children and adults
- Limited to epidermis
What organism causes Impetigo?
- S. aureus
- GAS
Nonbullous impetigo clinical presentation
- red macule becomes a vesicle which ruptures, forming erosion with honey-colored crusting (more prominent than bullous type)
- usually face or extremities
Bullous impetigo clinical presentation
- vesicle progresses to flaccid bulla
- no surrounding erythema.
- bulla ruptures forming honey-colored crust
- favors intertriginous areas
Dx of impetigo
Gram stain or Bacterial cultures can be obtained but not necessary
Tx of impetigo
-Antibacterial wash
Localized impetigo can be treated with topical medications including:
- Mupirocin (Bactroban) ointment
- Retapamulin (Altabax) ointment
Other tx of impetigo
- more widespread impetigo may require oral antibiotics, such as first-generation cephalosporins, dicloxacillin, amoxicillin/clavunate, or azithromycin
- refer for severe or persistent disease that does not respond to therapy
Define folliculitis
- infection of hair follicle with +/- pus in the ostium of follicle
- begins in the upper portion of the hair follicle
PE of folliculitis
- follicular papule, pustule, or crust at the follicular infundibulum
- can extend deeper into the entire length of the follicle (sycosis)
Causes of folliculitis
1 is always bacteria - staph or strep (mainly staph)
Bacteria, fungi, virus and mites
S/sx of folliculitis
Usually nontender or slightly tender, may be pruritic
*Can progress to abscess or furuncle formation
Predisposing factors of folliculitis
- shaving hairy regions
- occlusion of hair-bearing areas
- topical corticosteroid preparations
- diabetes mellitus
- and immunosuppression
Organisms causing folliculitis
-bacteria
S. aureus;Pseudomonas aeruginosa(hot-tub)
Organisms causing folliculitis
-viral
Herpetic, molluscum contagiosum
Organisms causing folliculitis
-fungal
Candida, Malassezia, dermatophytes
Organisms causing folliculitis
-other
Demodex
Dx of folliculitis
- diagnosis made clinically
- cultures from intact pustules may isolate the causative organism
- skin scrapings may identify folliculitis caused bydemodexorpityrosporum
Tx of bacterial folliculitis
-mild
mild cases may be managed by topical disinfectant skin washes (eg, benzoyl peroxide, Dial soap, benzalkonium chloride, chlorhexidine, and bleach baths) +/- topical antibiotic (erythromycin, clindamycin)
Tx of bacterial folliculitis
-mod or severe
moderate or severe cases often requires 10 to 15 days of the appropriate oral antibiotic- dicloxacillin, amoxicillin, cephalosporins anddoxycycline- usually for 7 to 10 days
*10 days is normal treatment time
Hot-tub folliculitis is caused by…
Pseudomonas Aeruginosa
-following immersion in contaminated spa/pool water
PE of hot-tub folliculitis
- follicular-based papules and pustules of the trunk and lower extremities
- areas covered by bathing suits and axillae more prone
S/sx of hot-tub folliculitis
Fever, lymphadenopathy, and otitis externa (swimmer’s ear) may also rarely be associated with hot tub folliculitis
Tx of hot-tub folliculitis
- typically self-resolving, within 1 to 2 weeks, as long as one stays out of contaminated water
- severe cases: oral ciprofloxacin 500mg orally twice daily for 7 days
Define furuncle
AKA “boil”
- deep-seated inflammatory nodule that develops around a hair follicle
- arise in hair-bearing sites, particularly in regions subject to friction, occlusion, and perspiration, such as the neck, face, axillae, and buttocks
Furuncle etiology
- Often occur in the setting of staphylococcal folliculitis
- Majority of patients otherwise healthy
- Often more extensive with diabetes
Organism that causes furuncle
Staphylococcus aureus (SA) is the MCC - Methicillin sensitive (MSSA) or methicillin resistant (MRSA)
Furuncle on PE
-Hard, tender, red folliculocentric nodule, up to 1-2 cm
-Hair-bearing skin
-Enlarges and becomes painful and fluctuant (abscess) +/- pustule
-Zone of cellulitis may surround
Solitary or multiple lesions
Define carbuncle
- larger, more serious inflammatory lesion than furuncle with a deeper base
- composed of several to multiple, adjacent, and coalescing furuncles
- nape of the neck, the back, or thighs
Carbundle on PE
- Red, indurated nodule/plaque with multiple pustules, draining externally around multiple hair follicles
- Develops a yellow–gray irregular crater at the center
- **Extremely painful
- Fever and malaise are often present
- Results in scarring
Define abscess
- initially an erythematous nodule with formation of a pus-filled cavity
- commonly occur in folliculocentric infections: folliculitis, furuncles, and carbuncles
- can occur at sites of trauma, foreign bodies, burns, or insertion of intravenous catheters
What organism should you think of when you think of abscess?
CA-MRSA should be suspected in all patients with abscess
Etiology of Furuncle, Carbuncle, Abscess
- Extensive furunculosis or carbuncle/abscess may be associated with leukocytosis
- Diagnosis by clinical appearance
- Obtain culture from pus
- S. aureus is almost always the cause - CA-MRSA more than likely
Surgical tx of Furuncle, Carbuncle, Abscess
- Local application of moist heat (warm compress)
- Large, painful, and fluctuant lesions need I&D in a timely manner
- Simple incision with #11 scalpel blade: drainage with evacuation of the pus, probing the cavity to break up loculations
- Wound can be packed with iodoform gauze to encourage further drainage
- Draining lesions should be covered to prevent autoinoculation and diligent hand washing performed
Pharm tx of Furuncle, Carbuncle, Abscess
- *With surrounding cellulitis, associated fever or central facial involvement, need systemic antibiotic
- MSSA: dicloxacillin, cephalexin, clindamycin, doxycycline, minocycline, and trimethoprim sulfamethoxazole
- MRSA: clindamycin, doxycycline, minocycline, and trimethoprim sulfamethoxazole
- MRSA treat with intranasal mupirocin (Bactroban) ointment twice a day for 5-7 days and antibacterial wash
Define cellulitis
- Acute spreading infection of the dermis and subcutaneous tissue
- Common cause of inpatient hospital admissions
Organisms that cause cellulitis
- *S. aureus or Group A Strep
- Pathogens gain entry via any break in the skin or mucosa
- Tinea pedis and leg/foot ulcers common portals
Cellulitis risk factors
- chronic venous / arterial insufficiency
- edema
- surgery
- intravenous drug use
- body piercing
- human and animal bites
- diabetes
- hepatic cirrhosis
- immunosuppression
- and neutropenia
Clinical presentation of cellulitis
- Acute onset of localized erythema, induration and tenderness
- Erythema rapidly spreads and becomes intense
- Borders may be ill-defined and surface crusts may develop
- Overlying epidermis may have bulla formation or necrosis, resulting in extensive areas of epidermal sloughing and superficial erosion
- Lymphangitis and regional lymphadenopathy may be associated
- Usually presents in a unilateral distribution
Systemic symptoms of cellulitis
fever, chills, and malaise are variable, and may precede localizing signs
Dx of cellulitis
- Dx generally made clinically
- Epidermal swabs rarely helpful: organism found likely to be a colonizer or contaminant rather than a true pathogen
- Uncommon for blood cultures skin bx for culture or skin aspirates to be +
- Open wound: higher probability of + culture
Define Erysipelas
Acute beta-hemolytic group A streptococcal infection of skin involving superficial dermal lymphatics
S/sx of Erysipelas
- Local redness, heat, swelling
- Highly characteristic sharply demarcated raised indurated border
- Surface findings are often described as peau d’orange (skin of an orange)
Erysipelas vs. cellulitis
-More sharply defined margin and the erythema is classically bright red: compared to cellulitis
Patient complaints with erysipelas
May be accompanied with malaise, chills, high fever, HA, vomiting and arthralgias
Most common sites for erysipelas
Legs and face MC sites
Predisposing factors for erysipelas
- surgical wounds
- fissures in nares, under the nose, between/under toes
- abrasions
- venous insufficiency
- obesity
- lymphedema
- chronic leg ulcers
