Bacteremia

Bacteremia is a medical term for the presence of viable bacteria in the circulating blood ¹. Bacteremia may result from ordinary activities such as vigorous tooth brushing, dental or medical procedures, or from infections such as pneumonia or a urinary tract infection (UTI). Bacteremia usually causes no symptoms, but sometimes bacteria accumulate in certain tissues or organs and cause serious infections. Having an artificial joint or heart valve or having heart valve abnormalities increases your risk that bacteremia will persist or cause problems. Untreated and clinically significant bacteremia progresses to systemic inflammatory response syndrome, sepsis, septic shock, and multiple organ dysfunction syndrome ². People at high risk of complications from bacteremia are given antibiotics before certain dental and medical procedures.

Usually, bacteremia, particularly if it occurs during ordinary activities, does not cause infections because bacteria typically are present only in small numbers and are rapidly removed from the bloodstream by the immune system. However, if bacteria are present long enough and in large enough numbers, particularly in people who have a weakened immune system, bacteremia can lead to other infections and sometimes trigger a serious bodywide response called sepsis.

Bacteria that are not removed by the immune system may accumulate in various places throughout the body, causing infections there, as in the following:

• Tissues that cover the brain (meningitis)
• The sac around the heart (pericarditis)
• The cells lining the heart valves and the heart (endocarditis)
• Bones (osteomyelitis)
• Joints (infectious arthritis)

In bacteremia, bacteria tend to lodge and collect on certain body structures, such as abnormal heart valves. Bacteria are particularly likely to collect on any artificial material present in the body, such as intravenous catheters and artificial (prosthetic) joints and heart valves. These collections (colonies) of bacteria may remain attached to the sites and continuously or periodically release bacteria into the bloodstream.

Bacteremia causes

Bacteremia may occur during:

• Certain ordinary activities
• Dental or medical procedures
• Certain bacterial infections
• Injection of recreational drugs

Ordinary activities sometimes cause bacteremia in healthy people. For example, vigorous toothbrushing can cause bacteremia because bacteria living on the gums around the teeth are forced into the bloodstream. Bacteria may also enter the bloodstream from the intestine during digestion. Bacteremia that occurs during ordinary activities rarely leads to infections.

Dental or medical procedures can lead to bacteremia. During dental procedures (as during tooth cleaning by a dental hygienist), bacteria living on the gums may become dislodged and enter the bloodstream. Bacteremia may also occur when catheters are inserted into the bladder or tubes are inserted into the digestive tract or urinary tract. Bacteria may be present in the area where the catheter or tube has been inserted (such as the bladder or intestine). So even though sterile techniques are used, these procedures may move bacteria into the bloodstream. Surgical treatment of infected wounds, abscesses (collections of pus), and pressure sores can dislodge bacteria from the infected site, causing bacteremia.

In some bacterial infections, such as pneumonia and skin abscesses, bacteria may periodically enter the bloodstream, causing bacteremia. Many common childhood bacterial infections cause bacteremia.

Injecting recreational drugs can cause bacteremia because the needles used are usually contaminated with bacteria, and people often do not properly clean their skin.

Bacteremia prevention

People who are at high risk of complications due to bacteremia (such as those who have an artificial heart valve or joint or certain heart valve abnormalities) are often given antibiotics before procedures that can cause bacteremia:

• Dental procedures
• Surgical treatment of infected wounds
• Insertion of bladder catheters

Antibiotics help prevent bacteremia and thus infections and sepsis from developing.

All healthcare workers also play an important role in the prevention of bacterial infections in the workplace. At the most rudimentary level, basic hand hygiene and the adherence to clean and sterile techniques is critical in preventing and decreasing the prevalence of bloodstream infections. Preventative practice starts not only at the beginning of a procedure but also throughout daily maintenance of line care. Even with strict adherence to infection control, many patients will succumb to a blood stream infection. Recognizing the predominant organisms associated within each clinical setting can prevent mortality as blood stream pathogens such as S. aureus, Pseudomonas aeruginosa, and Enterobacter species are associated with a higher mortality rate. Prevention also includes judicious use of antibiotics which must take into effect the risk and reward of antibiotic use. The rising prevalence of multi-drug-resistant bacteria has complicated treatment over the years and will continue to do so. This rise makes education, prevention, and adherence to protocol a necessity to counter the debilitating effects of bloodstream infections. Patient isolation, preventing airborne and contact infections are also key factors that must be controlled. Today, all healthcare facilities have an infectious disease committee which oversees the use of antibiotics, prescribing habits of healthcare providers and ensures that invasive and other bedside procedures are done under sterile conditions. The key to lowering the morbidity of bacteremia is the education of the healthcare provider ³.

Bacteremia symptoms

Usually, bacteremia that results from ordinary events, such as dental procedures, is temporary and causes no symptoms. Bacteremia that results from other conditions may cause fever. Chills and/or rigors do not need to present; however, the presence of such signs should clue your healthcare provider that a febrile patient is now bacteremic. If people with bacteremia have fever, a rapid heart rate, shaking chills, low blood pressure, gastrointestinal symptoms (such as abdominal pain, nausea, vomiting, and diarrhea), rapid breathing, and/or become confused, they probably have sepsis or septic shock.

The development of septicemia leading to sepsis and septic shock will commonly cause hypotension, altered mental status, and decreased urine output due to hypovolemia from leaking capillaries. As the infection disseminates, other organs can become affected causing acute respiratory distress syndrome (ARDS) and acute kidney injury ².

Bacteremia complications

Bacteremia complications include:

• Meningitis
• Endocarditis
• Osteomyelitis
• Sepsis
• Cellulitis
• Peritonitis

Bacteremia diagnosis

Determining the primary source of infection is critical in the management of a patient with bacteremia, as well as in the identification of the affected patient population. Common sources in hospitalized patients include the respiratory tract and indwelling catheters, specifically central venous catheters. Untreated urinary tract infections most commonly cause community-acquired bacteremia. Soft tissue and intraabdominal infections are not as common and are more prevalent in the post-operative surgical setting. Escherichia coli is the most common cause of gram-negative associated bacteremia, while Staphylococcus aureus is the most common gram-positive organism ⁴.

If bacteremia, sepsis, or septic shock is suspected, doctors usually take a sample of blood so they can try to grow (culture) the bacteria in the laboratory and identify it. If needed, doctors may try to culture bacteria from other samples (such as urine or sputum).

In the hospital setting, most patients at a minimum will require a chest x-ray and urinalysis with culture. A surgical patient may require CT imaging of the location of their surgery to assess for abscess or collection formation, as well as wound cultures for surgical site infections. Likewise, an intubated or patient presenting with the pulmonary disease will require sputum cultures. Patients with indwelling venous catheters, hemodialysis catheters, or ports should have their lines removed and tips cultured ⁵.

Bacteremia treatment

Bacteremia requires urgent and appropriate antibiotics. Delay in the administration of appropriate antibiotics is associated with increased morbidity and mortality. Empiric antibiotics should follow a logical approach based on the patient’s history and current disposition, for example, is the infection community or hospital acquired, what is the patient’s recent healthcare exposure, recent medical or surgical treatment, and what is the local antibiotic resistance. Gram stain, if applicable. Before a Gram stain is finalized, all patients should receive broad-spectrum antibiotics covering gram-positive and gram-negative bacteria which include extended-generation cephalosporins or a beta-lactamase inhibitor. Pseudomonas coverage is applicable for hospital-acquired bacteremia, as well as in a patient with recent health care exposure. Additionally, vancomycin should be added to cover resistant gram-positive organisms most notably methicillin-resistant resistant Staphylococcus aureus (MRSA). When the practitioner obtains the final cultures, antibiotics should be titrated to directed therapy starting with the gram stain, and eventually, antimicrobial susceptibility. There is no optimal duration of treatment. In most cases, antibiotic treatment should continue for seven to 14 days and should always be administered parenterally. Oral agents are recommended when patients have been afebrile for at least 48 hours and are otherwise clinically stable ⁶.

Bacteremia prognosis

Patients with bacteremia who are treated with antibiotics or observed have good outcomes. But rarely the bacteremia may cause endocarditis, osteomyelitis, pneumonia, cellulitis, meningitis sepsis and multiorgan dysfunction, followed by death. Over the past four decades, the availability of better antibiotics and vaccination have resulted in lower mortality rates in people of all ages. Prior to the era of vaccination, the mortality rates from bacteremia were over 20%. Today, the biggest concern in the development of antibiotic resistance which is now common against most organisms. Many guidelines have been developed to manage children and seniors with fever and bacteremia ⁷.

Children with occult pneumococcal bacteremia have a 6-17% risk of persistent bacteremia, a 2-5.8% risk of meningitis, and a 6-10% risk of other focal complications ⁸.

Of all focal infections that develop because of pneumococcal bacteremia, pneumococcal meningitis carries the highest risk for significant morbidity and mortality, including a 25-30% risk of neurologic sequelae such as deafness, mental retardation, seizures, and paralysis ⁹. The mortality rate of pneumococcal meningitis is 6.3-15%, and the overall mortality rate of pneumococcal bacteremia is 0.8% ¹⁰.

Neisseria meningitidis also causes bacteremia in infants and young children. Although the prevalence of meningococcal bacteremia is much lower than that of pneumococcal disease (see Causes), the morbidity and mortality rates are much greater. Children with meningococcal bacteremia have a 42-50% risk of developing meningitis; a 50% risk of developing serious bacterial infection such as septic shock, pneumonia, and neurologic changes; a 3% risk of developing extremity necrosis; and an overall mortality rate of 4% ⁹.

When untreated, Salmonella bacteremia carries a 50% risk of persistent bacteremia and can cause meningitis, sepsis, and death in infants younger than 3 months or in persons who are debilitated or immunocompromised ¹¹. However, in previously healthy children aged 3-36 months, the risk of meningitis or serious bacterial infection following Salmonella bacteremia is low ¹².

A study by McMullan et al ¹³ that analyzed the epidemiology of Staphylococcus aureus bacteremia in 1153 children and adolescents from Australia and New Zealand found that the mortality rate in children with bacteremia due to methicillin-susceptible Staphylococcus aureus treated with vancomycin was 14% (6 of 43) compared to 2.6% (22 of 851) in children who were received other medications.

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