Bacteraemia, the presence of living organisms in the blood, can occur in healthy people without causing symptoms. For example, viridans streptococci may transiently enter the blood during dental procedures or even when teeth are cleaned vigorously. Unless there is a focus on which they can settle and multiply, e.g. an abnormal heart valve, these organisms are normally cleared very rapidly from the blood. Other organisms invading the blood stream, such as Staphylococcus aureus or Escherichia coli, are less likely to be dealt with by the immune system and more likely to cause disease; this is referred to as septicaemia.
The organisms causing septicaemia may originate from one of the areas of the body which are normally colonised by microorganisms, such as skin, large bowel or genital tract. Alternatively, the source may be infection in a major organ such as kidney or liver.
Septicaemia can be complicated by metastatic septic lesions in organs or tissues. Examples include staphylococcal osteomyelitis, pneumococcal pneumonia and meningococcal meningitis. Outlines common sources of bacteria causing septicaemia, the causative organisms and examples of metastatic lesions.
Circulatory failure-the septic shock syndrome-is the most dangerous complication of septicaemia and is caused by Gram-positive, Gram-negative or fungal organisms. In HIV infection a septic shock syndrome has been described in response to mycobacteria in the blood.
Blood cultures are the most important initial investigation in septicaemia but if shock develops, tests of hepatic, renal and cardiopulmonary function and of coagulation must be performed and monitored.
Blood cultures are the most important initial investigation in septicaemia but if shock develops, tests of hepatic, renal and cardiopulmonary function and of coagulation must be performed and monitored.
The treatment of septicaemia involves prompt administration
of a broad-spectrum antibiotic or a combination of
antibiotics. The choice usually has to be made on an
empirical basis before the results of cultures are
available. Examples of initial therapy include
ceftazidime alone or an aminoglycoside such as
gentamicin plus a