Blood is normally sterile in healthy individuals. It is the main transport mechanism connecting all different parts of the body. As it serves as a transport system for oxygen, food materials, waste products and others round the body, it can also carry microbes (Eugene et al., 1998). However, it has no normal flora and the presence of microorganism in it indicates failure of the defence mechanisms to maintain its sterility. In many cases such a failure is transitory and of no clinical importance but in others, it is serious and life threatening. Lymphoid tissue is an important part of the defence system acting as a filter to intercept potentially invasive pathogens as well as being the headquarter of the lymphocytes on which immunity is heavily dependent. This filter system is however liable to clinically significant infections by intercepted pathogen and it is also the primary target for some factors of infection (Douglas et al., 1981). The involvement of blood, lymphatic system and heart in many infections give us the knowledge of the presence of bacteria in the blood.
Various authors have reported bacteraemia immediately after incision of an abscess, tonsillectomy and tooth extraction (Fischer et al., 1941; Murry et al., 1941). Robert et al. (1997) described bacteraemia as a transitory disease in which bacteria present in the blood are usually eliminated from the vascular system by the reticulo endothelial system with no harmful effect, but in host with reduced immunity, septicaemia results.