septicemia, invasion of the bloodstream by virulent bacteria that multiply and discharge their toxic products. The disorder, which is serious and sometimes fatal, is commonly known as blood poisoning. The invasive organisms are usually streptococci or staphylococci but may be any type of bacteria. Septicemia occurs most often in older people who have underlying disease that makes them more susceptible to the infection. The primary causes of septicemia are infection within the walls of the blood vessels, rapidly progressing tissue infections (osteomyelitis, cellulitis), virulent systemic disease (meningitis, typhoid), and local infections (abscess, carbuncle) that the defense mechanisms of the body are unable to contain. The microorganisms usually spread to other organs, such as the lungs, liver, and brain.

Symptoms of septicemia are fever (usually quite high), chills, low blood pressure, confusion, and rash; it often results in multiple organ failure if not treated promptly with antibiotics. The diagnosis can be confirmed with blood cultures for the organism or with blood tests for antibodies or high levels of white blood cells.

See also toxemia; toxic shock syndrome.

or blood poisoning

Invasion of the bloodstream, after surgery or infectious disease, by microorganisms—typically gram-negative (see gram stain) bacteria—and the toxins they release. The latter trigger immune responses and widespread coagulation in blood vessels. High fever, chills, weakness, and sweating are followed by a drop in blood pressure. Multiple infections are often present, requiring broad-spectrum antibiotics as well as drainage of foci of infection. Without immediate treatment, septic shock follows, with a mortality rate over 50percnt. Invasive technology and antibiotic-resistant bacteria in hospitals have made septicemia more severe and more common. Seealso bacteremia.

Learn more about septicemia with a free trial on Britannica.com.