Прогноз и профилактика

Morbidity and mortality are as great from anaerobic and mixed bacterial sepsis as from sepsis caused by a single aerobic organism. Anaerobic infections are often complicated by deep-seated tissue necrosis. The overall mortality rate for severe intra-abdominal sepsis and mixed anaerobic pneumonias tends to be high; B. fragilis bacteremia is associated with significant mortality, especially in the elderly and in patients with malignancy.

Preventive measures include early treatment of localized infection to prevent bacteremia and metastatic disease: debridement of necrotic tissue, removal of foreign bodies, reestablishment of circulation, and early antimicrobial treatment of traumatic wounds. Early surgical exploration, drainage, closure of bowel perforation, and antimicrobial treatment of penetrating abdominal wounds are essential. Bowel preparation (eg, with neomycin and erythromycin) should be performed on patients undergoing elective colonic surgery. Parenteral antibiotics can also be used prophylactically in the immediate postoperative period. Cefoxitin or a combination of either metronidazole or clindamycin with gentamicin or tobramycin may be used. In clean-contaminated surgery, prophylactic antibiotics given as a single dose before surgery and continued for 24 h after can reduce the postoperative infection rate of 20 to 30% to 4 to 8%.

Treatment

For deep-seated anaerobic infection, pus should be drained and devitalized tissue surgically removed. Antibiotics given in conjunction with surgery help to control bacteremia, reduce secondary or metastatic suppurative complications, and prevent local spread of infection around the surgical site.

Because anaerobic culture results may not be available for 3 to 5 days, an antibiotic usually must be started before definitive laboratory results are known. Antibiotics sometimes work even when some of the bacterial species in a mixed infection are resistant to the antibiotic, especially if adequate drainage is performed. Treating anaerobes in mixed infections reduces the number of organisms in wounds and the number of abscesses formed. Abscesses and inciting sites of infection, such as organ perforations, must be closed or drained. Devitalized tissue, foreign bodies, and necrotic tissue must be removed. Any closed-space infections, such as empyemas, must be drained, and, whenever possible, the blood supply should be reestablished. Septic thrombophlebitis may require vein ligation as well as antimicrobial therapy.

GI or female pelvic anaerobic infections, which likely contain B. fragilis, may be penicillin-resistant. Resistance has also been described for 2nd-generation cephalosporins and clindamycin. No single regimen has been shown to be superior. The following drugs have excellent in vitro activity and are effective: metronidazole, imipenem/cilastatin, piperacillin/tazobactam, ampicillin/sulbactam, meropenem and ticarcillin/clavulanic acid. Drugs that are somewhat less active in vitro but are usually efficacious include clindamycin, cefoxitin, and cefotetan. Metronidazole 500 to 750 mg IV q 8 h (for children, 30 mg/kg/day in three doses) given with an aminoglycoside (eg, gentamicin 5 mg/kg/day in three divided doses) can be used for intra-abdominal infection or any infection arising from a colonic source to cover enteric gram-negative flora. Serum levels of gentamicin should be monitored because of potential nephrotoxicity and ototoxicity. Clindamycin 900 mg IV q 8 h (for children, 30 mg/kg/day in three divided doses) is an alternative to metronidazole in this regimen. Metronidazole is active against clindamycin-resistant B. fragilis, has unique anaerobic bactericidal activity, and usually avoids the pseudomembranous colitis sometimes associated with clindamycin. Concerns about its potential mutagenicity have not been of clinical consequence. Cefoxitin and cefotetan have good anaerobic coverage. The best in vitro activity is shown by metronidazole, imipenem, meropenem, and the -lactam/ -lactamase combinations. All but metronidazole can be used as monotherapy since these drugs also have good activity against aerobes.

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