Overview
Bacteraemia means bacteria are present in the bloodstream. Brief, harmless bacteraemia happens commonly, for example after brushing teeth or dental work, and the immune system quickly clears the bacteria. However, bacteraemia can also come from an infection elsewhere in the body, such as a urinary tract infection, pneumonia or an infected line or wound, and can lead to sepsis, a life-threatening response to infection.
Bacteria in the blood can also settle in other places, such as heart valves (endocarditis), bones, joints or the spine. Bacteraemia is diagnosed with blood cultures and treated with antibiotics, along with finding and treating the source of infection.
When to get urgent help
Seek emergency care for signs of sepsis: high fever or very low temperature, shivering, confusion, fast breathing, fast heartbeat, mottled or pale skin, or passing little urine.
Causes and risk factors
- Urinary tract infections, the most common source
- Pneumonia
- Abdominal infections: gallbladder, appendix, bowel
- Skin and soft tissue infections, such as cellulitis and abscesses
- Medical devices: intravenous lines, urinary catheters, pacemakers, artificial joints
- Dental procedures and poor dental hygiene
- Injecting drug use
- Surgery
Risk factors include older age, weakened immunity, diabetes, kidney failure and dialysis, cancer treatment, recent surgery or hospital stay, and having medical devices.
Common bacteria include Escherichia coli, Staphylococcus aureus (including MRSA), Streptococcus species, Klebsiella and Enterococcus.
How it develops (pathophysiology)
Normal defences
The bloodstream is normally sterile. Barriers such as the skin and the linings of the gut, airways and urinary tract keep bacteria out. If bacteria do enter, immune cells in the blood, liver and spleen, along with antibodies and complement, rapidly destroy them.
What goes wrong
- Entry: bacteria enter the bloodstream from a local infection, through damaged barriers, via medical devices, or during procedures.
- Survival: if bacteria are numerous, resist immune killing (for example by forming capsules or biofilms on devices), or if the immune system is weak, they survive and multiply.
- Spread to other sites (metastatic infection): some bacteria, particularly Staphylococcus aureus, are good at attaching to damaged heart valves, bone, joints and artificial devices, forming new infections such as endocarditis, osteomyelitis, septic arthritis and abscesses.
- Systemic inflammation: bacterial components such as endotoxin (in Gram-negative bacteria) and toxins trigger immune cells to release large amounts of cytokines. This can lead to sepsis, with widening and leakage of blood vessels, low blood pressure and organ dysfunction.
Why the symptoms happen
- Fever and chills (rigors) are caused by cytokines acting on the brain's temperature centre.
- Fast heart rate and breathing reflect the body's response to infection and fever.
- Low blood pressure, confusion and reduced urine indicate sepsis and reduced blood flow to organs.
- Symptoms of the source, such as painful urination or cough.
- Back pain, joint pain or new heart murmur may indicate spread.
How treatment acts on the mechanism
Antibiotics kill bacteria in the bloodstream, chosen based on the likely source and later adjusted to culture results. Source control, such as removing infected lines, draining abscesses or treating the urinary tract, removes the reservoir of bacteria. Fluids and supportive care treat sepsis. Echocardiography and longer treatment are needed when bacteria such as S. aureus are involved, because of the risk of endocarditis and deep infections.
Types
- Transient bacteraemia: brief and usually harmless
- Primary bacteraemia: no clear source, or from an intravenous line
- Secondary bacteraemia: from an infection elsewhere
- Hospital-acquired or community-acquired
- By organism: Gram-positive (such as Staphylococcus aureus) or Gram-negative (such as E. coli)
Signs and symptoms
- Fever and shivering (rigors)
- Feeling very unwell
- Fast heartbeat
- Fast breathing
- Low blood pressure, dizziness
- Confusion, especially in older people
- Nausea or vomiting
- Symptoms related to the source of infection
- Sometimes no fever, especially in older or immunocompromised people
How it is diagnosed
- Blood cultures, taken from two sites before antibiotics where possible
- Blood tests: white cell count, CRP, lactate, kidney and liver function
- Urine tests and chest X-ray to look for the source
- Imaging of suspected sites, such as ultrasound or CT
- Echocardiogram for Staphylococcus aureus or suspected endocarditis
- Cultures from lines or devices
Possible complications
- Sepsis and septic shock
- Endocarditis
- Osteomyelitis and spinal infections
- Septic arthritis
- Abscesses in organs
- Infected prosthetic joints or devices
- Multi-organ failure
Goals of treatment
Treatment aims to clear bacteria from the blood, treat the source, prevent or treat complications, and support organs if sepsis develops.
Medicines
- Intravenous antibiotics, started promptly and adjusted to culture results
- Duration usually 7 to 14 days, longer for S. aureus or complications
- Oral antibiotics may be used to complete treatment in some cases
Other treatments
- Source control: removing infected lines or devices, draining abscesses, treating blocked urinary tracts or gallbladder
- Intravenous fluids and oxygen
- Intensive care for septic shock
Living with it and prevention
- Good hand hygiene, particularly in healthcare settings
- Careful care of intravenous lines and catheters, removing them when no longer needed
- Good dental hygiene
- Prompt treatment of infections
- Safer injecting practices and support services for people who inject drugs
- Vaccination against pneumococcus and other infections
Monitoring and follow-up
Repeat blood cultures may be needed to confirm clearance, especially with S. aureus. Temperature, symptoms and blood tests are monitored during treatment.
Outlook
Most people recover with prompt antibiotics and source control. Outcomes are worse with sepsis, S. aureus bacteraemia, older age and serious underlying illness.
Recovery depends on finding and treating the source of the infection. People who have had bacteria in the blood are often reviewed after treatment to make sure the infection has fully cleared, and any lines, devices or wounds that started it are checked or replaced.
Special considerations
- Older adults may have few typical symptoms
- People with artificial heart valves or joints are at higher risk of infection of these devices
- People on dialysis or chemotherapy are at higher risk
