Bacteremia, in the strictest sense, refers to viable bacteria in the blood. Asymptomatic bacteremia can occur in normal daily activities such as conducting oral hygiene and after minor medical procedures. In a healthy person, these clinically benign infections are transient and cause no further sequelae. However, when immune response mechanisms fail or become overwhelmed, bacteremia becomes a bloodstream infection that can evolve into many clinical spectrums and is differentiated as septicemia. Untreated and clinically significant bacteremia progresses to systemic inflammatory response syndrome (SIRS), sepsis, septic shock, and multiple organ dysfunction syndrome (MODS). 
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.
Geographic region, patient population, drug resistance, and infection prevention practices at each institution drive the causative organisms of bloodstream infections. Taking into account that older patients with multiple comorbidities are more likely to reside in community centers and be hospitalized, it is no surprise that they are at an increased risk of developing bacteremia. Traditionally gram-negative bacilli were the driving force for most hospital-acquired bloodstream infections in the United States and are still the most common organism associated with community-acquired bacteremia. However, with the onset of an aging population and device-related procedures, gram-positive aerobes have seen an increase in prevalence over the last two decades. 
All bacterial infections are dependent on the host immune system, which is affected by their genetic signature, as well as congenital and acquired deficiencies. Cellular innate and adaptive immune responses are responsible for initial microbe clearance, while the liver and spleen filter active bacteria in the circulating blood. In its most basic form, bacteria will begin to colonize at its primary source of location. At this point, the bacteria may become transient and clinically insignificant or can escape the host immune response and increase in number and become a local infection that can eventually migrate to other parts of the body. If the bacteria are viable and enter the circulating bloodstream, the infection still may spontaneously clear or progress to septicemia. The first barrier to bacterial invasion is the skin and mucosal surfaces. Conditions that interfere with these natural defense barriers commonly include medical procedures that pass through the skin and anatomical lumina. Additionally, events can precipitate defense breakdown via trauma, burns, ulcers, and the natural elements of aging.
The classical presentation in a bacteremic patient is the presence of a fever. Chills and/or rigors do not need to present; however, the presence of such signs should clue the provider that a febrile patient is now bacteremic. 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 (AKI).
Identifying or presuming the source of infection will dictate the diagnostic measures taken. There should be a low threshold for ordering labs and imaging since time is of the essence in preventing septicemia. Initial labs in all presumed bacteremic patients should include a lactate level and blood cultures; ideally, two sets assessing for aerobic and anaerobic organisms from each arm. 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 pulmonary disease will require sputum cultures. Patients with indwelling venous catheters, hemodialysis catheters, or ports should have their lines removed and tips cultured.
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? 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.
Infectious disease consultation is usually indicated.
As with most infectious diseases, preventive practice is critical in the outpatient and inpatient setting. All healthcare workers 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 are 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 bloodstream infection. Recognizing the predominant organisms associated with each clinical setting can prevent mortality as bloodstream pathogens such as S. aureus, Pseudomonas aeruginosa, and Enterobacter species are associated with a higher mortality rate. Prevention also includes the 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 that 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. an interprofessional team consisting of physicians, nurse practitioners, specialty care nurses, and pharmacists will improve outcomes. Pharmacists evaluate drug selection, doses, and interactions. Critical care and medical-surgical nurses administer treatments, monitor patients, and are crucial in the notification of the team as to changes in status. Infection control nurses often follow up to ensure the quality of care. [Level V]
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 has 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, but the bottom line is that one should always be aware of the potential of harm if the observation is selected as a method of treatment. [Level 5]
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