CUTANEOUS INFECTIONS Dr. Nancy Cornish Director of Microbiology Methodist and Children’s Hospitals

WHAT IS COVERED? Superficial Erythematous lesions Ulcers, Nodules Sporotrichoid lesions Sinus tracts Burn wounds Simple post-operative wound infections Complicated wound infections Crepitant cellulitis Necrotizing fascistic Gas gangrene with myonecrosis Bite wounds

What is not covered? Systemic diseases with skin manifestations Chicken pox Rocky mountain spotted fever Others Toxin mediated disease Toxic shock syndrome, others Parasitic infestations Scabies, others Viral diseases Orf (pox virus), others

SKIN INFECTIONS Primary - de novo, no obvious portal of entry Secondary - secondary to injury Localized or extensive Mono microbial or poly microbial

SKIN INFECTIONS Acute (staph folliculitis) Chronic (fungal infections)

Superficial Erythematous Lesions Erysipelas Painful, red, edematous, indurated KEY - sharply demarcated raised border Fever, chills, regional lymphadenopathy Causes: Group A strep (rare; Group C or G) Involves dermis, superficial lymphatics Diagnosis (Dx) is usually clinical Treatment (Tx) is penicillin

Superficial Erythematous Lesions Cellulitis Diffuse spreading infection of loose connective tissue of deeper layers of dermis KEY - ill defined margins Causes: Group A Strep Penicillin Staph aureus Dicloxacillin Rarely, Aeromonas, Vibrio from swimming in fresh, sea water

Cellulitis LAB DX, if needed Disinfect skin Aspiration of advancing margin of erythema If necessary, inject 0.1 to 0.5 ml sterile, non bacteriostatic, isotonic saline subcutaneously and aspirate back Plant blood, chocolate and broth 37°C

Cellulitis Success of Cultures at Diagnosis Blood cultures - 4% Soft tissue aspirate - 10% Skin punch biopsies - 20%

Superficial Erythematous Lesions Erysipeloid cellulitis Erysipelothrix rhusiopathiae (gram positive rod, catalase negative, H2S positive) Occupational disease Fisherman, butchers, abattoir workers, cooks Hands, fingers Painful purplish inflammation with red margin and central pallor Tx is penicillin

Erysipeloid LAB DX Gram stain/culture usually negative Full-thickness skin biopsy at margin of lesion after decontamination of skin surface Place in broth, 35°C, 5 days Subculture daily onto blood agar until positive

Superficial Erythematous Lesions Impetigo Small erythematous papules →vesicles → thick honey colored crusts Bullous form (associated with S. aureus) Causes - Group A strep, Staph aureus and community acquired methicillin resistant Staph aureus (CA-MRSA) Superficial intra-epidermal infection Tx is topical antibiotic or dicloxacillin Ecthyma is deeper form, leads to scarring

Impetigo LAB DX Usually clinical If bacterial cultures needed Clean lesion with alcohol Remove crust, culture base of lesion Bullous lesion - aspirate fluid Plant on blood agar, 37°C

Folliculitis, Furunculosis, Carbuncles Localized cutaneous abscesses Distinguished by size and extent of subcutaneous involvement

Folliculitis Dome shaped papules, pustules around a hair with rim of erythema

Folliculitis CAUSES Staph aureus Enterobacteriaceae (patients on long term antibiotics) Proteus Pseudomonas aeruginosa Associated with contaminated whirlpools, swimming pools, hot tubs Itchy rash, buttocks, hips, thighs, axillae apocrine sweat glands, occluded by bathing suit Other symptoms Low grade fever Malaise Earache (otitis externa) Painful breasts (mastitis)

Folliculitis LAB DX Treatment Usually not necessary and often negative Usually local Topical antibiotics Warm compresses

Furunculosis (Boil) Abscess destroys tissue around hair follicle

Carbuncles Deep, extensive abscess involving several hair follicles/sebaceous glands Systemic symptoms Fever Malaise Cellulitis Bacteremia

Furuncles/Carbuncles Occur where hair follicles are present and subject to friction and perspiration Staph aureus most common pathogen

Furuncles/Carbuncles Treatment Warm compresses Incision and drainage (I & D) Antibiotics, if necessary LAB DX Aspirated pus, collected after sterilization of skin Plant blood/MacConkey agar, 35°C

Paronychia Superficial infection of nail fold Acute; Staph aureus Drainage, warm compresses Chronic; Candida species Frequent immersion of hands in water Remove cause, topical antifungal medication

Paronychia Usually not necessary LAB DX: Usually not necessary Decontaminate skin surface with 70% alcohol collect aspirated/drainage pus Plant on blood agar, 35°C

Whitlow Purulent lesion on distal phalanx of finger often caused by a puncture wound Staph aureus Herpetic Whitlow is due to Herpes simplex often mistaken for bacterial paronychia How to distinguish herpetic Whitlow from pyogenic cause (bacterial) Medical, paramedical, dental occupation Satellite vesicles Pain disproportionate to physical findings Non tense pulp space Serous drainage (not purulent) HSV lesions, mouth or genitals

Staphylococcus aureus - Virulence Factors Catalase; enzyme attacks H2O2 cell defense system Fibrinolysins; breaks down fibrin clots Hyaluronidase; dissolves connective tissue Lipases; dissolves fat  lactamases; breaks down  lactam antibiotics “penicillin” and others

Staphylococcus aureus - Virulence Factors Contd. Hemolysins; kills PMN’s, lysis of RBC’s Exotoxins; kills neutrophils Exfoliatins; causes shedding of skin Enterotoxins; causes food poisoning, vomiting, diarrhea Toxic shock syndrome toxin 1 (TSST-1) Panton-Valentine leukocidin→punches holes in WBCs (Mostly found in community acquired MRSA)

Streptococcus pyogenes (Group A Strep) - Virulence factors Capsule of hyaluronic acid; prevents phagocytosis M protein; helps prevent phagocytosis and intracellular killing Streptolysin O and S; toxic to a variety of cell types (also responsible for hemolysis on blood agar) Exotoxins; cause rash of scarlet fever, TSS Hyaluronidase; breaks down connective tissue Streptokinases; lysis fibrin clots

Whitlow LAB DX - HSV Decontaminate skin surface Firmly sample base of lesion, aspirate vesicles Submit in viral transport media Direct fluorescent antibody rapid test (DFA) Culture Treatment - HSV Acyclovir LAB DX - Bacterial Usually not needed Culture aspirate of pus on blood agar, 37°C Treatment - Bacterial Dicloxacillin or Clindamycin

Cutaneous Fungal Infections (Superficial Mycoses) Involve the keratinized layer of the epidermis, hair or nails Causes Dermatophytes Candida spp. Malassezia spp.