An infection that is in the bloodstream is called a systemic infection. Systemic diseases such as flu and typhoid affect the entire body. Bacteria can enter the circulatory and lymphatic systems through acute infections or breaches of the skin barrier or mucosa. Breaches may occur through fairly common occurrences, such as insect bites or small wounds. Even the act of tooth brushing, which can cause small ruptures in the gums may introduce bacteria in to the circulatory system. In most cases, the Bacteremia result from such common exposure is transient and remains below the threshold of detection.
In severe cases, bacteremia can lead to septicemia with dangerous complication such as Toxemia sepsis and Septic shock. In these situations, it is often the immune response to the infection that result in the clinical signs and symptoms rather than microbes themselves.