ANAEROBIC AND NECROTIZING INFECTIONS

ANAEROBIC AND NECROTIZING INFECTIONS - Ruben Peralta, MD, FACS; Hongyi Cui, MD, PhD
BASICS
DESCRIPTION
• Necrotizing infection of the skin and fascia are called necrotizing cellulitis and necrotizing fasciitis respectively.
• Anaerobic and necrotizing infections may be associated with gas in tissue.
• Necrotizing fasciitis is a rapidly spreading and potentially fatal soft-tissue infection located in the deep fascia, with secondary necrosis of the subcutaneous tissue. Organisms spread from the subcutaneous tissue along the deep fascial planes, presumably facilitated by bacterial enzymes and toxins.
• Type I necrotizing fasciitis is a mixed infection caused by the synergistic effect of both aerobic and anaerobic bacteria; Type II necrotizing fasciitis refers to a monomicrobial infection caused by group A -hemolytic streptococcus (GAS).
• Gas gangrene is a subset of necrotizing myositis usually caused by the Clostridium species with gas formation within the tissue.
• Necrotizing skin and soft-tissue infection is usually associated with extensive destruction of tissue, systemic toxicity, loss of limb, and even death.
ALERT
Geriatric Considerations
Increased risk with age >60
GENERAL PREVENTION
• Avoidance of trauma
• Good care of skin
• Control of diabetes
• Avoidance of tight orthopedic casts
• Follow routine surgical principles for skin closure
EPIDEMIOLOGY
• Predominant age: Any age
• Predominant sex: Male = Female
Incidence
Incidence of necrotizing faciitis 1,000-1,500 cases annually in the US
Prevalence
Rare
RISK FACTORS
• Tissue poor blood supply
• Old age
• Trauma
• Diabetes mellitus
• Malnutrition
• Immune suppression (e.g., HIV, malignancies, steroid use, etc.)
• Chickenpox
• Cigarette smoking
• Alcoholism
• Obesity
• Intravenous drug abuse
• Surgery
ETIOLOGY
Necrotizing fasciitis often begins as a cutaneous injury, which could be minor; a necrotizing process then begins below the dermis and spreads radially.
ASSOCIATED CONDITIONS
See "Risk Factors."


DIAGNOSIS
SIGNS AND SYMPTOMS
• Most important symptom is pain out of proportion to exam
• Malaise, anorexia
History
Most common predisposing conditions: Most cases arise from previous trauma or infection (surgical wound from open or laparoscopic procedure, ulcers, burns, IV drug injection site, abscess). May develop without apparent cause.
Physical Exam
The diagnosis of necrotizing fasciitis is clinical, based on physical exam
• Localized erythema and edema
• Skin discoloration with vesicle formation
• Foul odor
• Fever, often low grade early in the disease
• Tachycardia, hypotension
• Diaphoresis
• Rapidly spreading skin lesion
TESTS
Lab
• No test result is diagnostic, except frozen section biopsy of the fascia. Treatment should not be delayed while awaiting biopsy. Diagnosis is made clinically.
• Cultures and sensitivity tests for microorganisms reported to produce gas in human tissues
- Gram-positive anaerobes
 Cocci: Peptostreptococcus (anaerobic Streptococcus) (usually with group A streptococci [Streptococcus pyogenes, beta-hemolytic streptococci] or Staphylococcus aureus)
 Bacilli: Clostridium perfringens and other clostridia
- Gram-negative aerobes: Bacilli: Escherichia coli, Klebsiella pneumoniae, Enterobacter species, Proteus species (all usually in mixed infections)
- Gram-negative anaerobes: Bacilli: Bacteroides fragilis (usually with other gram-negative bacilli)
• With severe gangrene, studies will reveal anemia and leukocytosis.
• Gram smears for many possible organisms
• Daily serum creatine kinase
• Elevated liver functions may result from release of bacterial toxins.
• Renal dysfunction may occur secondary to hypotension and myoglobinuria.
• Drugs that may alter lab results
- Antibiotics before culture
Imaging
• Plain radiographs
- Gas in tissues; foreign body if present
• CT
- Soft-tissue swelling and presence of gas in tissues
Diagnostic Procedures/Surgery
Immediate surgical intervention, with longitudinal incisions of skin, superficial fascia, deep fascia, and muscles to look for and remove necrotic tissue and/or foreign bodies
• Multiple daily surgical interventions may be required.
Pathological Findings
Soft-tissue necrosis, with polymorphonuclear cells and vascular thrombosis
DIFFERENTIAL DIAGNOSIS
Other soft-tissue infection including abscess and post-surgical wound infection
TREATMENT
GENERAL MEASURES
• Infectious disease consultation, if available
• IV fluids with electrolyte repletion, if indicated
• Daily complete blood count and electrolytes in acute phase
• Prophylaxis for tetanus
• Hyperbaric oxygen in selected cases
Diet
By mouth, as tolerated
Activity
Bed rest
SPECIAL THERAPY
Hyperbaric oxygen
• Unclear therapeutic value
• No delay of surgical intervention for hyperbaric oxygen therapy
MEDICATION (DRUGS)
• Initially broad-spectrum antibiotic regimen, then tailor to organisms identified by blood and wound cultures and organism sensitivities. (1)[B]
• Initial broad spectrum coverage should include penicillin, which will provide coverage of Streptococcus, and clindamycin, which works synergistically with penicillin when large bacterial load is present and also binds Group A Steptococcus toxin.
• Aminoglycosides will cover enteric Gram-negative organisms.
• Metronidazole is an alternative to clindamycin for treatment of anaerobic organisms.
• For vibrio species, tetracycline can be used.
• Retrospective studies suggest there may be a survival benefit with the use of Intravenous Immunoglobulin (IVIG) therapy. IVIG works by binding toxins and binds superantigens which suppresses pro-inflammatory mediators. (2)[B]
• Important: Do not delay treatment even if smear, cultures, and tests are negative.
• Unlike Clostridia perfingens and group A -hemolytic streptococci, the Aeromonas species are uniformly resistant to penicillin-G but are reported highly sensitive to 3rd-generation cephalosporins.
• Precautions: Delay of operative treatment is an important determinant of increased morbidity and mortality.
SURGERY
• Necrotizing soft tissue infections are a surgical emergency. Patients should be taken to the operating room once the diagnosis is made.
• All necrotic tissue should be resected. Dissection should be carried along all involved fascial planes. Preservation of tissue should not take precedence over adequate debridement.
• If a limb is involved, amputation might be necessary because of extensive fascial and subcutaneous soft tissue necrosis and overwhelming systemic toxicity.
• Adequate surgical treatment can rarely be accomplished with a single operation. Debridement should continue until all necrotic tissue is removed. Multiple debridements is the norm.
• Negative pressure suction dressing (i.e., VAC dressing) may be utilized to improve wound care and assist with postoperative fluid management.
• Wound coverage and reconstruction can be undertaken once systemic sepsis has been controlled, all nonviable tissue has been removed and local bacterial control in the wound has been achieved.
FOLLOW-UP
DISPOSITION
• Following surgical debridement, patients should be monitored and managed in an ICU setting if clinically indicated.
• Close contacts of patients and health care workers do not require chemoprophylaxis with antibiotics. (3)[B]
PROGNOSIS
• Mortality for necrotizing fasciitis decreased to 14% in 2002 from nearly 28% in 1994. (4)[B]
• Risk factors for mortality are associated with the following: Pre-existing and concurrent health conditions age >60 years, male, malnutrition, IV drug abuse, bacteremia, history of pulmonary or heart disease or carcinoma.
COMPLICATIONS
• Tissue and functional losses
• Amputation
• Fulminant course leading to death without treatment
PATIENT MONITORING
• As clinically indicated; may include following cultures, electrolytes, drug levels
• May require surgical critical care management in an ICU.
• Diligence required to recognize spreading gangrene
REFERENCES
1. Elliott D, Kufera JA, Myers RA. The microbiology of necrotizing soft tissue infections. Am J Surg 2000;361-366.
2. Norrby-Telund A, Low DE. Group A Streptococcal Toxic Syndrome and Necrotizing Fasciitis. Current Treatment Options in Infectious Diseases 2003;5,419-429.
3. Smith A. Invasive group A streptococcal disease: Should close contacts routinely receive antibiotic prophylaxis? Lancet Inf Dis 2005;5:494-500.
4. MMWR, 2005 51(53) 11 and MMWR 1994;43:401.