Bloodstream infections
Bloodstream infections (BSIs) occur when infectious microorganisms, primarily bacteria, enter the bloodstream, leading to a serious condition known as bacteremia. These infections can arise from various sources, including existing infections in wounds, the skin, the lungs, or urinary tract, and can sometimes be triggered by medical procedures involving catheters. While not all cases of bacteremia progress to widespread infection, those that do can lead to severe complications like sepsis, which may result in organ failure and can be life-threatening.
Individuals with compromised immune systems, chronic diseases, or those undergoing certain medical treatments are at a higher risk of developing BSIs. Symptoms often begin with chills and fever, but can escalate to confusion and significant changes in vital signs. Early diagnosis and treatment are critical; blood cultures are typically used to confirm the infection, and broad-spectrum intravenous antibiotics are administered rapidly to combat the infection.
Preventative measures focus on proper hygiene and infection control, particularly in medical settings, to reduce the risk of catheter-related infections. Despite the challenges posed by bloodstream infections, timely medical intervention can significantly improve outcomes.
Bloodstream infections
- ANATOMY OR SYSTEM AFFECTED: Blood, cardiovascular system
- ALSO KNOWN AS: Bacteremia, blood poisoning, hematogenous infection, sepsis, septicemia
Definition
A bloodstream infection is characterized by the presence of large numbers of infectious microorganisms in circulating blood. The causative infectious agents are most often bacteria, leading to bacteremia, but may also be viruses, fungi, or parasites. Bacteria and other microorganisms multiplying in the bloodstream release harmful toxins, creating conditions sometimes referred to as "blood poisoning." Infectious organisms in circulating blood may spread infection throughout the body, leading to sepsis. However, not all bacteremia develops into widespread infection.
Initially, blood flow near an existing infected area may carry infective organisms into the bloodstream. Capillaries, the smallest blood vessels in the vascular system, may then transport microorganisms into organ tissue, sometimes affecting the function of body organs such as the heart, lungs, and kidneys and causing systemic infection. Other biological factors can accelerate this process, including immune mediators, special infection-activated white blood cells, pro-inflammatory mediators, and coagulation factors.
Rapidly spreading bloodstream infection may overwhelm the body’s immune system, resulting in a systemic inflammatory response (sepsis) with abnormal blood coagulation and interruption of oxygen delivery to body tissues. Sepsis is a serious complication of bloodstream infection that can progress to organ failure, severe hypotension, septic shock, and death. The seriousness and progression of bloodstream infection depends on a person’s underlying health status and immune response.
Causes
Bloodstream infection may begin with bacteria migrating from an existing infection site, such as an open wound, a puncture wound, a burn, an ulcer, an infected prosthetic device, or a urinary tract infection. Other causes of bloodstream infection include infection of the skin (such as soft tissue infection or cellulitis), heart (endocarditis), lungs (such as pneumonia or a lung abscess), or kidneys (such as pyelonephritis). Even a tooth abscess or dental work may cause oral infection that enters the bloodstream.
Common external sources of infection are indwelling intravascular and urinary catheters that are used frequently in persons in acute and long-term care. Central venous catheters are the most frequent cause of nosocomial (hospital-acquired) bloodstream infection; hemodialysis catheters are also common causes.
Causative bacteria that have been identified in bloodstream infections include Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, pneumococcal and streptococcal organisms, and Acinetobacter, Klebsiella, and Bacteroides species. A definite source of infection is found in only 30 to 50 percent of all cases.
Risk Factors
Surgery, injury, and placement of indwelling catheters present high risk for bloodstream infection. Risk is increased in persons with existing acute or chronic infection, chronic disease (such as diabetes), or chronic alcoholism, and with persons who use IV (intravenous) drugs. People with compromised immune response, including older adults, young children, persons with human immunodeficiency virus (HIV) infection or other immune disorders, and those being treated with chemotherapy, corticosteroids, or immunosuppressive drugs following transplantation, are at greater risk for bloodstream infection.
Symptoms
Alternating chills and fever with prostration are early symptoms of bloodstream infection. Other symptoms vary depending on the primary infection site and overall health status. Progressive symptoms include mental confusion, changes in breathing and heart rate, and reduced urine output. Increased heart rate or low blood pressure may develop if the condition progresses rapidly toward sepsis.
Screening and Diagnosis
Early confirmation of a bloodstream infection is crucial, and finding the infection source is important to treatment. A physical examination of the person’s symptoms and health history may help locate existing infections. Infection derived from an intravenous catheter is suspected in hospitalized patients when no open wounds, urinary tract infection, or other obvious sources exist, especially if the intravenous line has been in place for one week or more. A history of kidney infection, kidney stones, or prostate disease suggests urinary tract infection, as does decreased mental function or confusion in older adults.
Blood culture is the primary diagnostic measure in confirming bacteremia. The presence of any type of infection, fever of unknown origin, recent surgery, or placement of indwelling catheters, calls for a blood culture. The doctor will order a complete blood count with white-cell differential and will likely order an elevated white blood cell count. If routine urinalysis points to a urinary tract infection, the doctor will order a urine culture and a urine Gram’s stain.
Chest X-rays may be taken to exclude lung tumors, pneumonia, or other lung infections. Diagnostic imaging such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) may help identify or exclude an infection source, especially intra-abdominal infection. Hospitalized persons who have abnormal vital signs and respiratory or cardiac symptoms will need to be evaluated for evidence of sepsis.
Treatment and Therapy
An aggressive approach is crucial when a bloodstream infection is suspected or confirmed. The core treatment for infection is intravenous broad-spectrum antibiotics, administered to eliminate the causative organism and prevent progression to sepsis. Ideally, antibiotic therapy is begun within two hours of a physical examination. Culture results may suggest a change in the type of antibiotics used in treatment. These antibiotics include piperacillin/tazobactam, cefepime, meropenem, and ceftriaxone. Vasopressor medications may also be used to increase blood pressure, and oxygen is commonly given to aid in recovery.
Removing an infected catheter can be a critical step. Intravenous (IV) fluids, including blood transfusion, may be given depending on urinary output. A respirator or oxygen may be needed to assist with breathing difficulty. Surgery is sometimes needed to drain an abscess or other localized infection. Oral antibiotics will be given for some time after the infection has diminished. Rarely, if kidney infection results in subsequent kidney failure, hemodialysis may be required.
Prevention and Outcomes
Bloodstream infection cannot always be avoided, but seeking treatment early is important if fever or other signs of infection develop, particularly after injury or surgery, or in IV drug users. Hospital infection-control measures help prevent catheter-related bloodstream infections. These measures include the aseptic catheter insertion technique, the use of antibiotic-coated catheters, the use of chlorhexidine in central venous catheter protocols, and a reduction in the number of days catheters remain in place.
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