Bacteremia is the presence of bacteria in the bloodstream. It can occur spontaneously, during certain tissue infections, with use of indwelling genitourinary or IV catheters, or after dental, gastrointestinal, genitourinary, wound-care, or other procedures. Bacteremia may cause metastatic infections, including endocarditis, especially in patients with valvular heart abnormalities. Transient bacteremia is often asymptomatic but may cause fever. Development of other symptoms usually suggests more serious infection, such as sepsis or septic shock. Diagnosis is with culture. Treatment is with antibiotics.
(See also Neonatal Sepsis and Occult Bacteremia.)
Bacteremia may be transient and cause no sequelae, or it may have metastatic or systemic consequences. It may be intermittent, suggesting the presence of an undrained collection (eg, visceral or organ space), or persistent, as in endocarditis or other endovascular infection.
Systemic consequences include
Sepsis (previously referred to as systemic inflammatory response syndrome)
Etiology of Bacteremia
Bacteremia has many possible causes, including
Catheterization of an infected lower urinary tract
Surgical treatment of an abscess or infected wound
Colonization of indwelling devices, especially IV and intracardiac catheters, urethral catheters, and ostomy devices and tubes
Gram-negative bacteremia secondary to infection usually originates in the genitourinary or gastrointestinal tract or in the skin of patients with pressure injuries. Patients who are chronically ill or immunocompromised have an increased risk of gram-negative bacteremia. They may also develop bacteremia with gram-positive cocci and anaerobes, and are at risk of fungemia. Staphylococcal bacteremia is common among patients who inject illicit drugs, patients with IV catheters, and patients with complicated skin and soft-tissue infections. Bacteroides bacteremia may develop in patients with infections of the abdomen and the pelvis, particularly the female genital tract.
If an infection in the abdomen causes bacteremia, the organism is most likely a gram-negative bacillus. If an infection above the diaphragm causes bacteremia, the organism is most likely a gram-positive coccus or bacillus.
Pathophysiology of Bacteremia
Transient or sustained bacteremia can cause metastatic infection of the meninges or serous cavities, such as the pericardium or larger joints. Metastatic abscesses may occur almost anywhere. Multiple abscess formation is especially common with staphylococcal bacteremia.
Bacteremia may cause endocarditis, most commonly with staphylococcal, streptococcal, or enterococcal bacteremia and less commonly with gram-negative bacteremia or fungemia. Patients with structural heart disease (eg, valvular disease, certain congenital anomalies), prosthetic heart valves, or other intravascular prostheses are predisposed to endocarditis. Staphylococci can cause bacterial endocarditis, particularly in people who inject illicit drugs, and usually involving the tricuspid valve. Staphylococcus is also the most common cause of hematogenously spread vertebral osteomyelitis and diskitis.
Symptoms and Signs of Bacteremia
Some patients are asymptomatic or have only mild fever.
Development of symptoms such as tachypnea, shaking chills, persistent fever, altered sensorium, hypotension, and gastrointestinal symptoms (abdominal pain, nausea, vomiting, diarrhea) suggests sepsis or septic shock. Bacteremia is detected in > 40% of patients who develop septic shock. Sustained bacteremia may cause metastatic focal infection or sepsis.
Diagnosis of Bacteremia
Cultures
If bacteremia, sepsis, or septic shock is suspected, cultures of blood and any other appropriate specimens are obtained.
Treatment of Bacteremia
Antibiotics
In patients with suspected bacteremia, empiric intravenous antibiotics are given after appropriate cultures of potential sources and blood are obtained. Early treatment of bacteremia with an appropriate antimicrobial regimen seems to improve survival.
Continuing therapy involves adjusting antibiotics according to the results of culture and susceptibility testing, draining any abscesses, and usually removing any internal devices that are the suspected source of bacteria.
Once source control is achieved and clinical improvement is observed, therapy can be completed with appropriate oral antibiotics. Deep-seated sources of infection (eg, endocarditis, endovascular infection, osteomyelitis) have historically been treated with long courses of IV antibiotics, but recent studies have shown transition to oral therapy can be successful for some of these infections (1, 2).
Treatment references
1. Iversen K, Ihlemann N, Gill SU, et al. Partial Oral versus Intravenous Antibiotic Treatment of Endocarditis. N Engl J Med. 2019;380(5):415-424. doi:10.1056/NEJMoa1808312
2. Li HK, Rombach I, Zambellas R, et al. Oral versus Intravenous Antibiotics for Bone and Joint Infection. N Engl J Med. 2019;380(5):425-436. doi:10.1056/NEJMoa1710926
Key Points
Bacteremia may be transient and of no consequence or lead to metastatic focal infection or sepsis.
Bacteremia is more common after invasive procedures, particularly those involving indwelling devices or material.
If bacteremia is suspected, give empiric antibiotics after cultures of potential sources and blood are obtained.
