Download LAB DX

CUTANEOUS INFECTIONS
Dr. Nancy Cornish
Director of Microbiology
Methodist and Children’s Hospitals
Sinus Tracts
LAB 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 structures
Follow surgery or trauma
Severe, rapidly progressive high mortality rate
Anaerobes 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 Infections
 LAB 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 You
Any questions?
[email protected]