ABSTRACT

Pilonidal abscess Arises from infection of a pre-existing pilonidal sinus. Gram-negative anaerobic organisms and Bacteroides fragilis are often the cause.

Perianal abscess Infection of hair follicles caused by Staphylococcus aureus. This organism is often responsible for abscess formation wherever it causes disease; examples include lung abscesses, psoas abscesses (see below), meningitis and brain abscesses, etc.