Cause:Bacteroides fragilisand other species; anaerobic streptococcus; microaerophilic streptococcus

Pathophys:Abscess formation very often; almost always 2 or more organisms; perivascular localization causes thrombophlebitis

Sx: Brain abscess extrasubdural empyema; peridontal abscess; lung abscess; appendiceal/diverticular abscesses; hepatic abscess; PID/septic abortion; sinus abscess

Si:Putrid pus (fatty acids); palpable gas in tissues, but r/o gas gangrene, or E. coligas formers in diabetic

Indolent, may be relatively asymptomatic for months

Thrombophlebitis often

r/o clostridial gas gangrene, which has incubation <3 d, marked toxemia, severe pain, lots of swelling, necrotic blistered skin, minimal gas, sweet smell, gas extension and infection into muscle, which is all in contrast to anaerobic infections

Lab:Bact:Culture anaerobically

Rx:

Anticoagulate with low threshold because of DVT predisposition

Antibiotics (Med Let 1999;41:95):

• Clindamycin; with gentamicin if may have aerobes; ampicillin alone ok in PID if not too toxic; better than penicillin in pulmonary abscess (Ann IM 1983;98:466 vs 1983;98:546); often used with penicillin for brain abscess
• Metronidazole (Flagyl) po or iv; cidal vs all anaerobes except microaerophilic gram-positives; diffuses well into abscess spaces
• Amoxicillin + clavulanic acid (Augmentin)/ampicillin + sulbactam (Unasyn)/piperacillin + tazobactam (Zosyn)
• Penicillin G, or ampicillin, ~10 million U qd; for brain abscess, perhaps with chloramphenicol
• Chloramphenicol; can be used alone for brain abscesses or w penicillin
• Cefoxitin or cefotetan; are 90% effective vs bacteroides
• Imipenem + cilastatin (Primaxin)