General Information

• What is bacteraemia?
• How serious is it?
• Where does bacteraemia come from?
• Can more than one organism cause a bacteraemia at the same time?
• How is bacteraemia diagnosed?
• How long does bacteraemia last?
• How is bacteraemia treated?
• Is the HPA monitoring cases of bacteraemia?

What is bacteraemia?

Bacteraemia occurs when bacteria get into the bloodstream. Bloodstream infection is also sometimes called septicaemia, which implies greater severity/clinical significance. A wide variety of bacteria can cause bacteraemias, the two most common being Staphylococcus aureus and Escherichia coli.

How serious is it?

Bacteraemia can be short-lived and the patient remain asymptomatic (without symptoms). It can however persist and lead to patients being severely ill with clinical signs of sepsis (fever, rigors etc.). 

Where does bacteraemia come from?

Bacteria can enter the bloodstream by a variety of routes, including localised sites of infection in the body (e.g. the urinary tract or the lung) that spill over into the bloodstream.  Bacteria on the skin may also invade the bloodstream directly through breaks in the skin such as cuts or surgical incisions, or when intravenous catheters are used. 

How is bacteraemia diagnosed?

Bacteraemia is diagnosed when blood samples from the patient are sent to the microbiology laboratory where any infecting bacteria are cultured and identified. At this point the microbiology laboratory will also test the bacteria for susceptibility to antibiotics in order to guide patient treatment. 

In some apparent bacteraemias the organism may not be from the blood but may instead be a contaminant; it may have been present on the skin and contaminated the blood during the process of the blood being drawn, leading to what's known as a 'pseudobacteraemia'. It is also possible that a blood sample may become contaminated with an organism during the laboratory culturing and identification process.

Can more than one organism cause a bacteraemia at the same time?

Yes. When more than one organism is isolated from the same blood culture, e.g. E. coli and S. aureus, this condition is called a 'polymicrobial' bacteraemia. Detection of a polymicrobial bacteraemia can have important therapeutic implications as a combination of (two or even more) anti-microbial agents may be required to effectively treat both organisms. However, some of the organisms in polymicrobial bacteraemias may be contaminants - for example, from the skin - and do not require treating. Approximately 8% of bacteraemias are polymicrobial (HPA. Polymicrobial bacteraemias and fungaemias in England, Wales, and Northern Ireland).

How long does bacteraemia last?

Bacteraemia can persist for days or weeks and successful treatment relies on eradicating the underlying source of infection, for instance, draining an abscess. However, bacteraemias can be short-lived, lasting only a matter of hours without producing any ill-effects. These short-lived bacteraemias which normally go unnoticed and are cleared rapidly by the body's immune defences, are called 'transient' or 'silent' bacteraemias. They commonly involve bacteria from the mouth which can enter the bloodstream following activities such as tooth-brushing or vigorous chewing. A tiny minority of patients, usually those with pre-existing heart damage, may be at risk of developing an infection of the heart valves, a condition known as endocarditis.

How is bacteraemia treated?

If the patient is clinically ill, they will require treatment with appropriate antibiotics. The particular antibiotic required will vary depending on the species of bacteria causing the infection and the severity of the illness.  Treatment options may be complicated if the strain of bacteria is resistant to one or more commonly used antibiotics.

Is the HPA monitoring cases of bacteraemia?

The HPA undertakes surveillance of bacteraemia by collecting information from hospital microbiology laboratories.  For some organisms ( Staphylococcus aureus and glycopeptide-resistant enterococci) it is mandatory for hospitals to supply data but for other species of bacteria data are supplied on a voluntary basis.  In addition, sentinel surveillance is undertaken where isolates are sent in by sentinel laboratories for centralised testing for susceptibility to antibiotics.  These data allow trends in antibiotic resistance to be monitored, including detection of emerging antibiotic resistance.