PRINCIPLES OF PROPHYLAXIS AGAINST METASTATIC INFECTION
Metastatic infection is defined as infection that occurs at a location physically separate from the portal of entry ofthe bacteria. The classic and most widely understood example of this phenomenon is bacterial endocarditis, which arises from bacteria that can be introduced into
the circulation as a result of tooth extraction. The incidenceof metastatic infection can be reduced if antibiotic administration is used to eli minate the bacteria before they can establish an infection at the remote site.
For metastatic infection to’ occur, several conditions, must be met (Box 15-10). The first and most important is that there must be a susceptible location in which an infection can be established. The deformed heart valve
with its altered endothelial surface onto which a sterile vegetation has formed is an example of this. There also must be bacterial seeding of the susceptible area. This seedi. g occurs as the result of a bacteremia in which bacteria from the mouth are carried to the susceptible site. Most likely.a quantitative factor is involved in this seeding process, because the body has multiple episodes of small bacteremias as a result of normal daily
activities. More than likely, bacteremias with large quantities of bacteria are necessary to produce metastatic infection. The duration of the bacteremia may also playa role. In-some situations (e.g., total joint replacement) a prolonged high-level bacteremia, or septicemia, is usually
necessary to es tablish a metastatic infection. It is important to remember that the bacteremia after oral surgery is usually completely eliminated by the body’s reticuloendothelial system within 15 minutes after completion
of the surgery. Also neces sary for the establishment of metastatic
infection is som e impairment of the local host defenses.