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Bacteremia

What It Is, Causes, Signs and Symptoms, Treatment, and More

Author: Emily Miao, PharmD

Editors: Alyssa Haag, Lily Guo, Kelsey LaFayette, DNP, Jessica Reynolds, MS


What is bacteremia?

Bacteremia refers to the presence of bacteria in the bloodstream and can be caused by a variety of bacterial organisms including gram-positive (i.e., gram-positive bacteremia) or gram-negative bacteria (i.e., gram-negative bacteremia). In healthy individuals, small amounts of bacteria can be transiently introduced into the blood from interruption of skin and soft tissue barriers (e.g., scraping of the skin) and minor medical procedures (e.g., dental procedures). This is usually benign since the body’s host defenses are able to detect and eradicate these organisms. However, immunocompromised individuals with weakened immune systems may not be able to mount a strong immune response, and therefore, even small amounts of bacteria can eventually lead to pathologic bacteremia (i.e., bloodstream infection). If the bacteremia is left untreated, it may progress to sepsis (i.e., a serious clinical syndrome characterized by life-threatening organ failure caused by a dysregulated host response to infection). 

Urinary bladder with indwelling catheter.

What causes bacteremia?

Bacteremia occurs when bacteria enter the bloodstream.  Skin and mucosal surfaces are the first barrier to bacterial invasion. The body’s immune system is then responsible for the detection and clearance of bacteria. When these barriers and host defenses are impaired, large colonies of bacteria are able to grow and colonize exponentially at its primary site of infection. Eventually, the bacteria originating from the localized site may spread to other parts of the body, including the bloodstream. Examples of localized bacterial infection include urinary tract infections (e.g., cystitis from indwelling catheters); skin and soft tissue infections (e.g., cellulitis), bone infections (e.g., osteomyelitis, septic arthritis), and lung infections (e.g., pneumonia). Risk factors for bacteremia include immunocompromised states (e.g., history of chronic steroid use, cancer, HIV); older age; medical procedures that involve manipulation of the skin or mucosa (e.g., dental procedures, surgeries); disruption of skin and/or mucosal surfaces (e.g., trauma, burns, ulcers); and indwelling catheters or ports. 

If left untreated, bacteremia may also lead to sepsis or septic shock. Sepsis is a serious clinical syndrome characterized by life-threatening organ failure caused by a dysregulated host response to infection, while septic shock is defined as sepsis with accompanying signs of shock (e.g., dangerously low blood pressure).

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What are the signs and symptoms of bacteremia?

Signs and symptoms of bacteremia include a variety of constitutional symptoms including fever, chills, rigors, and night sweats, however, these symptoms may not always be present. The bacteremia may have originated from a localized infection, therefore infectious signs and symptoms based on the primary site of infection may also be present. For example, in a urinary tract infection, individuals may notice foul-smelling urine and experience dysuria, urinary frequency, and/or suprapubic pain. If pneumonia is present, an individual may also experience shortness of breath, cough, and/or sputum production. If left untreated, bacteremia may progress to sepsis or septic shock. Individuals may have hemodynamic instability including tachycardia, low systolic blood pressure (i.e., <100 mmHg), altered mental status, tachypnea (i.e., respiratory rate >22 breaths per minute), and signs of organ failure (i.e., decreased urine output).

How is bacteremia diagnosed?

Diagnosis of bacteremia begins with a thorough review of symptoms and medical history, including recent procedures; history of intravascular device placement; and recent localized infection. Obtaining vital signs and performing a thorough physical exam helps identify characteristics of sepsis and the presence of indwelling catheters or devices that could be potential sources of infection. Initial laboratory tests include a complete blood count, which may show an elevated or low white blood cell count; two sets of blood cultures assessing aerobic and anaerobic organisms from different sites; a basic metabolic panel to assess for organ dysfunction; a lactate level, as elevated levels may be indicative of sepsis; and additional infectious work-up in order to rule out localized sources of infection (e.g., urinalysis, chest X-ray, echocardiogram).

How is bacteremia treated?

Treatment of bacteremia is aimed at eradicating any potential localized sources of infection and decreasing the bacterial burden via intravenous (IV) antibiotics. Source control is achieved by removing any indwelling catheters, ports, or intravascular devices that could either introduce bacteria into the bloodstream or serve as a nidus for colonization. Broad-spectrum empiric intravenous antibiotics are often started after blood cultures are drawn. A few examples that cover gram-positive organisms include penicillins (e.g., ampicillin, nafcillin) and cephalosporins (e.g., cefazolin) for methicillin-susceptible Staphylococcus aureus (MSSA); glycopeptides (e.g., vancomycin) for methicillin-resistant staphylococcus aureus (MRSA); and oxazolidinones (e.g., linezolid) for vancomycin-resistant enterococcus (VRE). For gram-negative organisms, several antibiotic choices are available, including antipseudomonal agents that provide coverage for Pseudomonas aeruginosa, a highly virulent gram-negative bacterium. Examples of such agents include piperacillin-tazobactam, cefepime, and meropenem

Once blood cultures and sensitivities return, broad-spectrum antibiotics can be switched to an agent that is targeted to the specific organism. Daily blood cultures may be obtained to monitor the clearance of bacteremia. If the bacteremia progresses to sepsis or septic shock, escalation of care to the intensive care unit (ICU) may be warranted. Adjunctive treatment for sepsis syndromes includes intravenous fluids for rehydration and pressors (e.g., norepinephrine) to increase blood pressure and restore perfusion. Treatment duration depends on the local source that led to the bacteremia and the time required to clear the bacteremia. Finally, an infectious disease clinician can also be helpful in providing further guidance on the choice of antibiotic therapy and treatment duration.

What are the most important facts to know about bacteremia?

Bacteremia refers to the presence of bacteria in the bloodstream and can be caused by a variety of bacterial organisms. Risk factors immunocompromised states; older age; medical procedures that involve manipulation of the skin or mucosa; disruption of skin and/or mucosal surfaces; and presence of indwelling catheters or ports. Signs and symptoms of bacteremia include a variety of constitutional and infectious symptoms including fever, tachycardia, chills, rigors, and night sweats. Diagnosis is established through two sets of blood cultures and adjunct laboratory testing (e.g., complete blood count, and urinalysis). Treatment includes broad-spectrum empiric intravenous antibiotics and the removal of any indwelling catheters or intravascular devices that can potentiate the infection. 

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Related links

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Resources for research and reference

Arcens M, Stirnemann J, Mayor G, John G. Epidemiology and strategy to prevent urinary catheters related complications. Rev Med Suisse. 2018 Aug 29;14(616):1518-1521.

Howell MD, Davis AM. Management of sepsis and septic shock. JAMA. 2017;317(8):847-848. doi:10.1001/jama.2017.0131

IDSA Practice Guidelines for the Treatment of Methicillin-Resistant Staphylococcus aureus Infections in Adult and Children: https://academic.oup.com/cid/article/52/3/e18/306145 

Kern WV, Rieg S. Burden of bacterial bloodstream infection-a brief update on epidemiology and significance of multidrug-resistant pathogens. Clin Microbiol Infect. 2020;26(2):151-157. doi:10.1016/j.cmi.2019.10.031

Lewis PO, Heil EL, Covert KL, Cluck DB. Treatment strategies for persistent methicillin-resistant Staphylococcus aureus bacteraemia. J Clin Pharm Ther. 2018;43(5):614-625. doi:10.1111/jcpt.12743