Anaerobic infections. The basics for primary care physicians.

Anaerobic bacteria constitute a major portion of the normal human microflora, and some of them can cause disease in contiguous body parts, especially if there is a mucosal break. Most anaerobic infections are polymicrobial. Because anaerobes are difficult to culture, diagnosis is often made on the basis of clinical clues. Thus, knowledge of the common sites, predisposing conditions, and other representative features of anaerobic infections is critical. For anaerobic infections above the diaphragm, where Bacteroides fragilis is not a common isolate, high-dose penicillin G therapy is usually sufficient. Addition of clindamycin (Cleocin) or metronidazole (Flagyl, Metryl, Protostat) may be necessary for serious infections. Cefoxitin sodium (Mefoxin) or clindamycin is adequate for most anaerobic infections occurring outside the central nervous system. Metronidazole, chloramphenicol, imipenem, or beta-lactam antibiotics combined with beta-lactamase inhibitors may be preferable for serious infections. Appropriate coverage for aerobic bacteria must be included in the treatment regimen. Drainage of abscesses, decompression of infected spaces, debridement of necrotic tissue, and removal of foreign bodies are critical in management of many anaerobic infections.