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Bacteremia is the presence of bacteria in the bloodstream. It can occur spontaneously, during certain tissue infections, with use of indwelling GU or IV catheters, or after dental, GI, GU, 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.

Bacteremia may be transient and cause no sequelae, or it may have metastatic or systemic consequences. Systemic consequences include systemic inflammatory response syndrome and septic shock.

Etiology

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 GU or GI tract or in the skin of patients with decubitus ulcers. Chronically ill and immunocompromised patients have an increased risk of gram-negative bacteremia. They may also develop bacteremia with gram-positive cocci, anaerobes, and fungi. Staphylococcal bacteremia is common among injection drug users and patients with IV catheters. 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 gram-positive.

Pathophysiology

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 enterococcal, streptococcal, or staphylococcal 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 injection drug users, and may involve the tricuspid valve.

Symptoms and Signs

Some patients are asymptomatic or have only mild fever. Development of symptoms such as tachypnea, shaking chills, persistent fever, altered sensorium, hypotension, and GI symptoms (abdominal pain, nausea, vomiting, diarrhea) suggests sepsis or septic shock. Septic shock develops in 25 to 40% of patients with significant bacteremia.

Diagnosis

If bacteremia, sepsis, or septic shock is suspected, cultures are obtained of blood and any other appropriate specimens, as described elsewhere in The Manual.

Treatment

   Antibiotics

 In patients with suspected bacteremia, empiric antibiotics are given after appropriate cultures are obtained. Early treatment of bacteremia with an appropriate antimicrobial regimen appears to improve survival. Continuing therapy involves adjusting antibiotics according to the results of culture and susceptibility testing, surgically draining any abscesses, and usually removing any internal devices that are the suspected source of bacteria.

資料來源：Merck manuals