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Bacteremia

Dr. Suvansh Raj NirulaMBBS

February 23, 2021

February 23, 2021

Bacteremia
Bacteremia

Bacteremia refers to the presence of bacteria in the blood. Blood is a sterile medium and bacteria do not generally appear in it. However, even simple acts like brushing or minor medical procedures can transiently introduce bacteria into the blood. While not all types of bacteremia are symptomatic, some can establish bloodstream infection or septicemia. The body’s immune system fights septicemia with an appropriate, and usually adequate, immune response. Sepsis is the term used to refer to the exaggerated and dysregulated immune response of the body to ward off this bloodstream infection. Such an immune response often results in widespread organ damage. Signs and symptoms of sepsis are pronounced and can often prove fatal. At times, in severe sepsis, the patient’s blood pressure can fall dangerously low causing irreparable damage by altered cellular metabolism. This is called septic shock and has a staggeringly high mortality rate.

(Read more: Bacterial infection)

How bacteremia occurs

Bacteria can invade the bloodstream by various different routes:

  • Dental procedures: After teeth cleaning or tooth extraction, bacteria can enter the blood through the gums. Bacterial infection of the heart (endocarditis) is also possible.
  • Minor surgical procedures or major surgeries
  • Intensive Care Unit (ICU) stay: Hospital-acquired infections caused by antibiotic-resistant strains of bacteria is a common danger associated with ICU admissions.
  • From infections in other parts of the body. Common examples amongst others include:
    • Pneumonia: Infection localised in the lungs
    • Meningitis: Infection in the coverings of the brain
    • Cellulitis: Infection of the skin and underlying tissue
  • In-dwelling medical devices: Tubings, like catheters, endotracheal tubes or chest drains that are inserted in the body to guide removal of fluids and secretions, can introduce bacteria into it.
  • Severe burns or injury: Burnt or injured tissue loses its vital blood circulation and becomes especially vulnerable to bacterial invasion. Therefore, burn patients are kept isolated under the strictest possible aseptic precautions.
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Types of bacteremia

Following are the types of bacteremia:

  • Bacteremia: Defined as the transient presence of bacteria in the blood that can be easily removed by the action of the host’s immunity.
  • Septicemia: Well-established bloodstream infection, also called blood poisoning. Usually occurs due to the spread of bacteria and their toxins from a site of localised infection through the blood. Common infections that can cause septicaemia include:
  • Sepsis: Sepsis is a life-threatening complication of untreated, or inadequately treated, septicaemia that triggers an exaggerated and unregulated immune response from the host. When bacteria enter the cells, the molecules present on them signal the immune system to kick start. Three processes occur because of this. First, the complement pathway is activated, leading to stimulation of blood-clotting cells (or platelets), which begin to form blood clots in a dysfunctional manner. These small clots, or thrombi, block the vessels which run through organ systems, causing deprivation of oxygen and ultimately death of organ tissue and organ failure. Second, the inflammatory response, mediated by cytokines starts. Although inflammation is necessary to combat bacteria, in sepsis it goes unregulated, resulting in a hyper-inflammatory state called the Systemic Inflammatory Response Syndrome (SIRS), which progresses to damage organs. Lastly, endothelial injury, caused by byproducts formed due to lack of oxygen, also contribute to organ dysfunction. Not all cases of bacteremia progress to sepsis. Some additional risk factors linked with the immune status of the patient could play a role:
  • Septic shock: Exaggerated inflammatory response associated with severe sepsis leads to a massive shift of fluid from the blood, resulting in volume depletion. The drop in blood pressure and a compensatory increase in heart rate produces shock.

Signs and symptoms of bacteremia

Septicaemia evokes an immune response. The attempt by the body to ward off infection can sometimes be exaggerated or dysregulated; this is termed as sepsis. The presentation of sepsis in adults and older children can typically be as follows:

  • Fever (body temperature higher than 38°C) or hypothermia (body temperature lower than 36°C)
  • Chills and shivers
  • Fast breathing
  • Rapid heartbeat
  • Confirmed infection anywhere in the body

Sepsis presents differently in younger children. Neonatal sepsis (from birth to 1 month of age) in babies is common but can be deadly. Signs to look out for are:

  • Fever (body temperature greater than 38°C in babies under three months or 39°C in those up to six months of age or if the child is apathetic) or hypothermia (body temperature below 36°C)
  • Difficulty breathing: Accompanied with grunting, punctuated by pauses (apnoea; temporary cessation of breathing) or child left unable to speak
  • Cold extremities
  • Baby unable to feed
  • Repeated vomiting
  • Lethargic or unconscious baby
  • Redness around the umbilicus in newborns
  • Abdominal swelling
  • Jaundice
  • Seizures

With a more severe bacterial infection, a greater immune response is generated and can cause severe sepsis or septic shock. The clinical picture in such case would additionally include:

Septic shock can also lead to or be accompanied by multiorgan dysfunction syndrome (MODS). This marks the beginning of the gradual shut down of the body and is a bad prognostic marker that often results in death. Sepsis-related organ damage is described as the dysfunction of at least two or more of the following organ systems in an acutely ill patient who needs intervention or intensive care unit (ICU) treatment. Six organ systems are taken into consideration:

  • Lungs and the respiratory system: Acute Respiratory Distress Syndrome (ARDS) is a result of fluid collecting in air sacs, called alveoli, of the lungs, preventing sufficient air intake and inadequate oxygenation of the lungs and other organs. Presents with laboured, rapid breathing. Can be associated with disorientation, confusion and lethargy.
  • Heart and the cardiovascular system: Damage to heart valves due to lack of oxygen can cause endocarditis. Heart failure can arise, causing impairment in the heart’s ability to pump out blood.
  • Kidneys and the renal system: The kidneys become incapable of filtering urine effectively. This reduces the urinary output as well as causes the buildup of toxins. (Read more: Chronic Kidney Disease)
  • Blood and the circulatory system: Volume depletion due to inflammation causes a fall in blood pressure and produces shock.
  • Liver and the hepatic system: At first, liver transaminases begin to rise and later, serum bilirubin increases as well, producing hyperbilirubinemia or jaundice.
  • Brain and the central nervous system: At first, disorientation and confusion set in due to lack of oxygen and toxin buildup; however, later permanent brain damage due to prolonged ischemia can occur.

Diagnosis of and test for bacteremia

As signs and symptoms can be non-specific or vague at times, laboratory investigations are paramount to correct diagnosis and obtain information on antibiotic sensitivity to adequately treat bloodstream infections.

Blood tests: 

  • Complete blood count: Based on the increase of certain infection-fighting white blood cells, bacteremia and septicaemia can be detected.
  • Blood glucose test: Blood sugar levels may be increased by bacterial activity.
  • Liver function test: Liver transaminases and serum bilirubin levels can be deranged by sepsis-induced organ dysfunction.
  • Kidney function test: This is essential to diagnose acute kidney injury or kidney failure by measuring the buildup of toxins removed by kidneys under normal circumstances.
  • Clotting studies: Blood prothrombin time (PT), activated partial thromboplastin time (aPTT) and thrombin time (TT) are tests that assess whether the blood is clotting normally or has become hypercoagulable (as it does in sepsis-induced disseminated intravascular coagulation where small thrombi in blood vessels block oxygen supply to organs, causing them to devitalise)
  • D-Dimer: A substance that also indicates the presence of thrombi.
  • Blood culture: It gives a definitive diagnosis of the presence of bacteria in blood and information on which antibiotics would work on them.
  • Arterial blood gases (ABG): A small sample of arterial blood is taken and concentration of electrolytes in blood is measured. It is useful in detecting metabolic acidosis, which can set in with organ failure.

Urine tests:

  • Urine microscopy: Presence of cells, pus or blood can point to infection.
  • Urine culture and sensitivity: In case of urinary tract infections, bacteria will be detected and information on antibiotic sensitivity will be obtained.

Imaging investigations: Following investigations, as per the doctor’s discretion, can help localise the nidus of infection within the body:

Other investigations:

  • Pulse oximetry: A small device (pulse oximeter) placed on the nail bed of a finger detects the oxygen saturation of venous blood in the body. SpO2 below 92% indicates desaturation and possible respiratory dysfunction.
  • Lumbar puncture: Tests the cerebrospinal fluid for the presence of bacteria or signs of infection. Useful in diagnosing brain infections.

Special, more invasive investigations may be used to detect the source of infection if the routine ones fail to guide diagnosis. Examples include bronchoscopy, lymph node biopsy, or even laparoscopic surgery.

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Treatment of bacteremia

Supportive treatment: In case of severe septicaemia and sepsis, patients require intensive care in the ICU.

  • Oxygen therapy: High-flow oxygen administration is often necessary in patients with undesirably low SpO2 values (who have become desaturated).
  • Intravenous fluid therapy: Fluids are needed to replace the volume displaced by the inflammatory process.
  • Serial sampling and monitoring: Of blood electrolytes, urine output, blood pressure, etc.
  • Dialysis: In case of kidney failure, the use of an artificial kidney system to remove toxins is essential.

Medical management:

  • Intravenous antibiotics: A broad-spectrum antibiotic may be initiated at first but it is soon upgraded to bacteria-specific ones after blood culture and sensitivity reports become available.
  • Vasopressors: These drugs help elevate falling blood pressure levels by their action on blood vessels. They help correct septic shock.
  • Bronchodilators: Medicines that help the patient breathe better may be administered if acute respiratory distress syndrome (ARDS) has set in.

Surgical management: Laparoscopic surgery may be recommended in some cases that call for the operative removal of the source of infection, like an abscess, present inside the body.

Prevention of bacteraemia

Most patients admitted to the intensive care unit (ICU), especially ones who are admitted following surgical procedures, are known to develop sepsis. Prevention of sepsis is not only possible but also essential.

Community setting

Measures to be taken on a personal and community level are the following:

  • Proper handwashing
  • Maintaining good personal hygiene
  • Ensuring cleanliness of the home and surroundings
  • Cooking food properly in a sanitary manner
  • Up-to-date vaccinations

(Read more: Vaccines for newborns, infants and children)

Healthcare setting

Measures to be taken on a hospital and healthcare level are the following:

  • Proper handwashing
  • Ensuring the use of properly sanitized and sterilised equipment
  • Use of disposable gloves
  • Prophylactic dose of antibiotics following surgical procedures
  • Regular changing of catheters and other tubings


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