Host factors predisposing to anaerobic infections.

Anaerobic bacterial infections of man are typically associated with locally comprised tissues and commonly also with a systemically compromised host. Thus, any condition that interferes with the systemic defence mechanisms of the host and thus predisposes to infection in general, increases the incidence of anaerobic infections also. It is generally true to say that anaerobic infections occur secondary to mechanical disruption of anatomical barriers, usually percutaneous in clostridial infections; in nonclostrial anaerobic infections the disrupted barriers are commonly mucosal surfaces where the offending organisms exist as the dominant part of normal bacterial floras. The most important single factor which enables anaerobes to flourish in the tissues is low oxygen tension which is usually the result in the first instance of a compromised blood supply and poor tissue perfusion. A variety of other predisposing factors may operate in concert, enabling the nonsporing anaerobes to cause a diversity of infective states in many different parts of the body. These host determinants are considered in relation to clostridial, nonclostridial and postsurgical anaerobic sepsis.