Glossary · Dysbiosis and disease
Bacteraemia
In one sentence
Bacteraemia is the presence of viable bacteria in the bloodstream, usually confirmed by blood cultures. It can be transient and harmless or part of a serious infection, and it is not the same as sepsis, which is defined by the body's response to infection.
Also known as: bacteremia · bacteraemias · bloodstream infection · catheter-related bacteraemia · bacteriemia
What is bacteraemia?
Blood is normally sterile. Bacteraemia means live bacteria are circulating in it; when the organisms are fungi, the term is fungaemia. It describes a microbiological finding rather than a level of severity: it covers everything from the brief passage of oral bacteria into the blood when chewing or brushing teeth to a bloodstream infection with high fever and systemic illness.
Types and causes
- Transient: lasts minutes, usually goes unnoticed and is cleared by the immune system in healthy people.
- Intermittent or persistent: recurs or continues, as with undrained abscesses or endocarditis.
- Primary: no identifiable source, or related to an intravascular catheter.
- Secondary: arises from a known source such as a urinary, abdominal, respiratory or skin infection.
Risk factors include lines and devices, immunosuppression, older age, dialysis, recent surgery and prosthetic material.
Bacteraemia and sepsis
They are not interchangeable. Under the Sepsis-3 consensus (Singer et al., JAMA, 2016), sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection. Bacteraemia may never lead to sepsis, and many patients with sepsis have negative blood cultures, either because the source does not seed the blood or because antibiotics were already given.
How it is diagnosed
The reference test is the blood culture. As well as confirming bacteraemia, it isolates the organism so that susceptibility can be tested and antimicrobial resistance detected. Interpreting a positive result takes judgement: a coagulase-negative staphylococcus in a single set is often a contaminant, whereas Staphylococcus aureus or E. coli in blood is almost always treated as significant.
When blood cultures are negative and suspicion remains, molecular tests and clinical metagenomics can detect bacterial DNA. Detecting DNA does not on its own prove that viable bacteria are present, and these methods complement culture rather than replace it.
Example
A haemodialysis patient with a central venous catheter develops a fever during a session. Blood cultures are taken from the catheter and from a peripheral vein. Both grow S. aureus, with the catheter sample flagging positive earlier, which points towards catheter-related bacteraemia. The team decides on antibiotic treatment and catheter management according to the susceptibility results and local protocols.
Bacteraemia at Xenogene
The product sheet for Xenogene’s AMC in Blood lists bacteraemia in immunocompromised patients among its priority indications, alongside sepsis and fever of unknown origin. The analysis looks for genetic material from bacteria, viruses, fungi, parasites and mycobacteria, together with resistance and virulence genes, in venous blood. The sheet advises considering possible contamination with Gram-positive cocci, notes that a negative result does not exclude infection and leaves interpretation to the clinical team.
Frequently asked questions
Is bacteraemia the same as sepsis?
No. Bacteraemia describes bacteria in the blood; sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection. You can have bacteraemia without sepsis, and sepsis with negative blood cultures.
Is bacteraemia serious?
It depends on the context. Transient bacteraemia, such as can follow tooth brushing or some procedures, usually clears on its own in healthy people. Bacteraemia from an active infection, by contrast, can be serious and needs prompt medical assessment and treatment.
How is bacteraemia diagnosed?
With blood cultures: several sets drawn with aseptic technique, ideally before antibiotics. If bacteria grow, they are identified and tested for antibiotic susceptibility. Molecular tests can add information in selected cases.
Related terms
- Blood culture
A blood culture incubates a blood sample in bottles of nutrient broth to find out whether live bacteria or fungi are circulating in the bloodstream. If anything grows, it is identified and tested against antibiotics to guide treatment.
- Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection (Sepsis-3 definition, 2016). It is a medical emergency that needs immediate treatment.
- Clinical metagenomics
Clinical metagenomics (mNGS) is the untargeted sequencing of the genetic material in a patient sample to detect bacteria, viruses, fungi or parasites without choosing the pathogen in advance. It complements culture and susceptibility testing rather than replacing them.
- Antimicrobial resistance
Antimicrobial resistance (AMR) is the ability of bacteria, viruses, fungi or parasites to stop responding to medicines that used to control them, making infections harder to treat.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
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