CUTANEOUS INFECTIONS
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Dr. Nancy CornishDirector of Microbiology
Methodist and Children’s Hospitals
CUTANEOUS INFECTIONS
Sinus TractsLAB DX:
– Surgical exploration to obtain deep tissue biopsies for cultures is BEST
– Poor correlation between results of culturing drainage/opening of fistula/sinus tract and cultures obtained from deeper infected tissues as surface specimens become colonized with bacteria/fungus
– Obtain blood cultures if systemic symptoms present fever, chills
– Granules (if present) should be collected crushed and cultured in cases of mycetoma
Burn Wounds
Quantitative culture definition:– Burn wound complications associated with > 105
organisms (CFU)/gram of tissue
Controversial– Surface cultures misleading due to colonization– Deep tissue biopsies, marked variation of number
of bacteria within tissue– Inability to estimate the depth to which organisms
have spread
Simple Postoperative Wound Infections
Wound is contaminated with bacteria– Patient’s own flora
– Caregiver’s flora
– Hospital environment flora
Predisposing Host Risk Factors
– Obesity
– Diabetes
– Vascular insufficiency
– Immune suppression
Microbial Risk Factors
– Microbial load (how many?)
– Virulence factors carried by bacteria
• S. aureus
• Group A strep
• Ps. aeruginosa
Surgical Risk Factors
– Duration of an operation
– Poor hemostasis
– Presence of foreign bodies
• Sutures
• Mesh
• Grafts
Simple Postoperative Wound Infections
In the presence of risk factors, the inoculums size necessary to initiate infection is much smaller than that required to cause infection in healthy tissues.
Simple Postoperative Wound Infections
LAB DX Important:– Best specimen aspirate of pus (at least 1 cc)– Gram stain– Plant blood, MacConkey agar at 37°C
TX:– Broad spectrum empiric therapy started based on
gram stain results if possible– Antimicrobial therapy tailored to culture results
when available
Complicated Wound Infections
Affects skin and subjacent structuresFollow surgery or traumaSevere, rapidly progressive high mortality rateAnaerobes involved, esp. Clostridium spp.
Complicated Wound Infections
3 Syndromes– Crepitant cellulitis
• Clostridial
• Non-clostridial
– Necrotizing fasciitis• Meleney’s gangrene (abdominal surgery)
• Fournier’s disease (perineum and scrotum)
– Gas gangrene with Myonecrosis• Associated with Clostridium perfringens
Complicated Wound InfectionsLAB DX
– Tissue and fluid cultures from surgery set up for aerobic and anaerobic work up and gram stain
(5 ml or grams of tissue)Gram stain often shows lack of white cells and
presence of bacteria and cellular debris– Blood cultures
TX– Surgical debridement ASAP!– Broad-spectrum antimicrobial therapy is
indicated to cover gram positive and gram negative organisms as well as anaerobes
Infections Complicating Bite Wounds
Oral flora of biter is injected into the bite– Human bites
• Severe necrotizing infections
• Aggressive treatment– Debridement
– Antibiotics
– Animal• Deep puncture wounds
• Unusual organisms– Pasteurella multocida (dogs/cats)
– Streptobacillus moniliformis (rats)
– Cat scratch disease (Bartonella henselae)
Bite Wounds
LAB DX:– Culture of fresh bite wound is unrewarding -
reveals only the oral flora of the biter– Culture, if needed, is best if aspirated pus taken
from depths of wound taken after infection develops
TX:– Should cover both aerobic and anaerobic
organisms = Amoxicillin/Clavulanic acid
For copies of specimen collection posters go to:
www.thepathologycenter.org
Thank YouAny questions?
Nancy.Cornish@nmhs.org
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