The aetiology of perirectal sepsis.

Organisms that are present in the normal faecal flora, especially Bacteroides fragilis, were isolated significantly more often from perirectal abscesses associated with a fistula. Other organisms similar to those associated with infection of obstructed apocrine glands at other sites were isolated from abscesses without fistulas. These findings suggest that perirectal abscesses with and without fistulas may have a different aetiology and that appropriate bacteriological investigation may give an indication of the presence of an unsuspected fistula and thus provide useful guidance to the correct surgical management of the patient. Staphylococcus aureus and other skin organisms were found less frequently than in previous studies on perirectal sepsis and were equally common in cases with or without a fistula-in-ano.