Bacteremia, Septicemia - Intravascular, Extravascular infections

Bacteremia, Septicemia

There are two major categories of bloodstream infections- Intravascular and extravascular blood infections.

Intravascular infections

Intravascular infections originate within the cardiovascular system. Since infections are within the vascular system, organisms are present in the bloodstream at a fairly constant rate (i.e. continuous bacteremia). It includes:

1. Infective endocarditis

2. mycotic aneurysm

3. suppurative thrombophlebitis

4. intravenous

5. catheter-associated bacteremia

Infective endocarditis

It is an infection inflammation of the endocardium (inner lining of the heart) where especially heart valves are involved. The infection is caused by cardiac abnormalities such as congenital valvular disease, direct trauma from IV catheters, etc.

Mycotic aneurysm

It results from damage to endothelial cells lining blood vessels. The infection causes inflammatory damage and the weakening of an arterial wall. This weakening causes a bulging of the arterial wall i.e. aneurysm that can eventually rupture.

* The causative agent is similar to that of endocarditis.

Suppurative thrombophlebitis

Suppurative thrombophlebitis inflammation of vein wall. The pathogenesis involves alternation in the vein's endothelial lining followed by clot formation

The site is then seeded with microorganisms, establishing the primary site of infection. It is a frequent complication in hospitalized patients (Intravenous catheters).

Intravenous catheter-associated bacteremia

Colonization of intravenous (IV) catheters by bacteria (also fungi) can lead to serious bloodstream infection and can result in nosocomial infection and even death. The infection can occur via 2 routes:

• via the lumen of catheters

• movement of microorganisms through the catheter entry site along the patient's skin down the external surface of the catheter and into the bloodstream

Slime-producing microorganisms such as Staphylococcus epidermidis can much more easily adhere to the catheter surface.

Extravascular infection

Microorganisms mostly reach blood circulation via the lymphatic system from another site of infection. In most individuals, bacteria in the blood are rapidly and effectively removed by the reticuloendothelial system in the liver, spleen, and bone marrow, and by circulating phagocytes.

In some individuals, most microorganisms in the blood are cleared. Some common portals of entry for bacteremia are:

• genitourinary tract (25%)

• respiratory tract (20%)

• abscess (10%)

• surgical wound infection (5%)

• biliary tract (5%)

• miscellaneous site (10%)

• uncertain site (25%)