Bacteraemia

bloodstream infection, blood poisoning

Bacteraemia occurs when bacteria enter the bloodstream, which is normally sterile and free from germs. While healthy people often clear these bacteria without symptoms, the condition can become serious if the immune system cannot cope, potentially leading to life-threatening complications.

Table of contents

• What is bacteraemia?
• How bacteria enter the bloodstream
• Signs and symptoms
• Who is at risk?
• Possible complications
• Diagnosis
• Treatment

What is bacteraemia?

Bacteraemia is the presence of bacteria in your blood. Normally, your blood is sterile, meaning it does not contain any bacteria or other germs^[1]. When bacteria do enter the bloodstream, healthy people can often clear them naturally without developing any illness^[2].

The condition can occur during everyday activities or result from medical procedures. In many cases, especially in people with strong immune systems, bacteraemia is temporary and causes no symptoms or health problems. The body’s immune system recognizes the bacteria and removes them naturally^[1].

However, when the immune system cannot fight off the bacteria effectively, or when it becomes overwhelmed, bacteraemia can develop into a more serious bloodstream infection. This is sometimes called septicemia, which refers to an established infection within the bloodstream^[2]. Without treatment, the condition can progress to sepsis, a dangerous body-wide response to infection, or septic shock, which causes dangerously low blood pressure and can lead to organ failure and death^[1][4].

How bacteria enter the bloodstream

Many different types of bacteria can cause bacteraemia. The most common ones include Escherichia coli (E. coli), Staphylococcus aureus (including resistant strains like MRSA), and various streptococcal species^[1]. Other bacteria that may cause bloodstream infections include Bacillus cereus, pneumococcal bacteria, Salmonella, and Pseudomonas aeruginosa^[1].

Bacteria can enter the bloodstream through various pathways. Common entry points include skin wounds such as cuts, scrapes, or burns. Even minor activities like brushing or flossing your teeth too vigorously can introduce bacteria into the blood^[1][4].

Medical and dental procedures are another significant route for bacteria to enter the bloodstream. These include dental work such as teeth cleanings or tooth extractions, surgical procedures, insertion of catheters or breathing tubes, and blood donations. The use of medical devices, particularly indwelling catheters and intravenous lines, can also lead to bacteraemia^[1][6]. Sharing or reusing needles is another risk factor^[1].

In hospitalized patients, the respiratory tract and indwelling catheters, especially central venous catheters, are common sources of infection. In the community, untreated urinary tract infections are the most frequent cause of bacteraemia^[2]. Infections from the gastrointestinal tract or skin can also spread bacteria into the bloodstream, particularly in people with weakened immune systems^[6].

Signs and symptoms

Many people with bacteraemia experience no symptoms at all, or only develop a mild fever. When the immune system recognizes bacteria in the blood, it typically removes them without causing noticeable illness^[1][6].

However, if bacteraemia progresses to sepsis or septic shock, more serious symptoms develop. These may include chills, fast heart rate (a condition called tachycardia), low blood pressure (known as hypotension), and rapid breathing (referred to as hyperventilation)^[1][6].

Additional symptoms that may appear include abdominal pain, nausea and vomiting, diarrhea, persistent fever, altered mental state, and shaking chills^[1][6]. The development of these symptoms usually indicates a more serious infection and requires immediate medical attention.

Who is at risk?

Certain groups of people face a higher risk of developing bacteraemia and its complications. People with weakened immune systems are particularly vulnerable, as they may be unable to fight off infections effectively^[1].

Older adults, especially those with multiple health conditions who live in community care facilities or require frequent hospitalization, are at increased risk of developing bacteraemia^[2]. Chronically ill patients and those with compromised immune function also face elevated risk^[6].

People who inject illicit drugs have a higher chance of developing staphylococcal bacteraemia. Those with indwelling medical devices such as intravenous catheters, urinary catheters, or prosthetic heart valves are also more susceptible^[6].

Patients with certain underlying conditions face particular risks. Those with structural heart disease, such as valvular problems or certain congenital abnormalities, are predisposed to developing endocarditis (an infection of the heart’s inner lining) if bacteria enter their bloodstream^[6].

Possible complications

Without proper treatment, bacteraemia can spread to other parts of the body and cause serious complications. The most critical risk is progression to sepsis, which can lead to organ failure and death^[1].

Bacteria traveling through the bloodstream can cause infections in various organs and tissues. These include cellulitis (a skin infection), endocarditis (infection of the heart valves or inner lining), meningitis (infection of the membranes surrounding the brain and spinal cord), osteomyelitis (bone infection), peritonitis (infection of the abdominal cavity lining), and pneumonia (lung infection)^[1].

Bacteraemia can also cause infections in the fluid-filled spaces around joints or the sac surrounding the heart. Multiple abscesses may form in various locations throughout the body, which is especially common with staphylococcal infections^[6].

In some cases, bacteraemia may be intermittent, suggesting the presence of an undrained collection of pus somewhere in the body. Persistent bacteraemia often indicates an ongoing infection in the blood vessels, such as endocarditis^[6].

Diagnosis

A healthcare provider diagnoses bacteraemia through a physical examination and by asking about symptoms, including how long they have been present. If bacteraemia is suspected, the provider will order specific tests to confirm the diagnosis^[1].

The primary diagnostic tool is a bacterial culture, which checks for the presence of bacteria in bodily fluids. During a blood test, the provider uses a thin needle to withdraw a small amount of blood, usually from a vein in the arm. This blood sample is then tested in a laboratory to see if bacteria are present and, if so, which type^[1].

Depending on the suspected source of infection, other samples may be collected. A sputum test examines thick, discolored mucus coughed up from deep in the lungs. A urine test checks for bacteria in the urinary system. If there is an infected wound such as a scrape, cut, burn, or abscess, the provider may take a sample of fluid or pus from the wound^[1].

The healthcare provider may also order imaging tests such as X-rays, computed tomography (CT) scans, or ultrasound to help determine where an infection might be located in the body^[1].

Treatment

The main treatment for bacteraemia is antibiotics. When a healthcare provider suspects bacteraemia, they will prescribe antibiotics even before culture results are available. This is called empiric treatment. Once the specific bacteria are identified through culture tests, the antibiotic treatment may be adjusted based on which bacteria are present and which antibiotics they are sensitive to^[6].

Starting antibiotic treatment early appears to improve survival rates in people with bacteraemia. The antibiotics are typically given intravenously, meaning through a vein, to ensure they reach the bloodstream quickly^[6].

Treatment also involves addressing the source of the infection. This may include draining any abscesses or collections of pus in the body. If the infection is related to a medical device such as a catheter, the device usually needs to be removed^[6].

Once the source of infection is controlled and clinical improvement begins, treatment typically continues until the infection is fully resolved. The duration of antibiotic therapy depends on the type of bacteria involved, the source of infection, and how quickly the patient responds to treatment^[6].