Serological diagnosis of Bacteroides fragilis infections by a complement fixation test

Paired specimens of serum from patients from whom Bacteroides fragilis had been isolated were tested by complement fixation against a crude B. fragilis antigen. A high titre or a rise in titre to B. fragilis was obtained in each of five patients with infection after abdominal surgery but in none of 11 patients with postpartum pyrexia nor in nine with vaginitis.