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Bloodstream infections ( BSIs) are infections of blood caused by blood-borne pathogens. The detection of in the blood (most commonly accomplished by ) is always abnormal. A bloodstream infection is different from sepsis, which is characterized by severe Inflammation or of the host organism to pathogens.
Bacteria can enter the bloodstream as a severe complication of (like pneumonia or meningitis), during surgery (especially when involving mucous membranes such as the gastrointestinal tract), or due to catheters and other foreign bodies entering the arteries or veins (including during intravenous drug abuse). Transient bacteremia can result after dental procedures or brushing of teeth.
Bacteremia can have several important health consequences. Immune responses to the bacteria can cause sepsis and septic shock, which, particularly if severe sepsis and then septic shock occurs, have high , especially if not treated quickly (though, if treated early, currently mild sepsis can usually be dealt with successfully). Bacteria can also spread via the blood to other parts of the body (which is called hematogenous spread), causing infections away from the original site of infection, such as endocarditis or osteomyelitis. Treatment for bacteremia is with antibiotics, and prevention with antibiotic prophylaxis can be given in high risk situations.
Bacteremia frequently evokes a response from the immune system called sepsis, which consists of symptoms such as fever, chills, and hypotension. Severe immune responses to bacteremia may result in septic shock and multiple organ dysfunction syndrome, which are potentially fatal.
| Bacteria | Bacteremia, in the strictest sense, refers to presence of 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. | ||
| Viremia is a medical condition where enter the and hence have access to the rest of the body. It is similar to bacteremia, a condition where bacteria enter the bloodstream. (2025). 9780838585290, McGraw Hill. ISBN 9780838585290 The name comes from combining the word "virus" with the Greek word for "blood" ( haima). It usually lasts for 4 to 5 days in the primary condition. | |||
| Fungi | Fungemia is the presence of fungus or in the blood. The most common type, also known as candidemia, candedemia, or systemic candidiasis, is caused by Candida species; candidemia is also among the most common bloodstream infections of any kind. Infections by other fungi, including Saccharomyces, Aspergillus (as in aspergillemia, also called invasive aspergillosiis) and Cryptococcus, are also called fungemia. It is most commonly seen in immunosuppressed or immunocompromised with severe neutropenia, cancer patients, or in patients with intravenous . | Candidemia, aspergillemia (invasive aspergillosis) | |
| Protozoemia (blood-borne protozoal infections) | Protozoa | Protozoan infections are parasitic diseases caused by organisms formerly classified in the kingdom Protozoa. These organisms are now classified in the supergroups Excavata, Amoebozoa, Harosa (SAR supergroup), and Archaeplastida. They are usually contracted by either an insect vector or by contact with an infected substance or surface. |
Staphylococcus aureus is the most common cause of healthcare-associated bacteremia in North and South America and is also an important cause of community-acquired bacteremia. Skin ulceration or wounds, respiratory tract infections, and IV drug use are the most important causes of community-acquired staph aureus bacteremia. In healthcare settings, intravenous catheters, urinary tract catheters, and surgical procedures are the most common causes of staph aureus bacteremia.
There are many different types of Streptococcus species that can cause bacteremia. Group A streptococcus (GAS) typically causes bacteremia from skin and soft tissue infections. Group B streptococcus is an important cause of bacteremia in Infant, often immediately following birth. Viridans streptococci species are normal bacterial flora of the mouth. Viridans strep can cause temporary bacteremia after eating, toothbrushing, or flossing. More severe bacteremia can occur following dental procedures or in patients receiving chemotherapy. Finally, Streptococcus bovis is a common cause of bacteremia in patients with colon cancer.
Enterococcus are an important cause of healthcare-associated bacteremia. These bacteria commonly live in the gastrointestinal tract and female genital tract. Intravenous catheters, urinary tract infections and surgical wounds are all risk factors for developing bacteremia from enterococcal species. Resistant enterococcal species can cause bacteremia in patients who have had long hospital stays or frequent antibiotic use in the past (see antibiotic misuse).
Among healthcare-associated cases of bacteremia, gram negative organisms are an important cause of bacteremia in the ICU. Catheters in the veins, arteries, or urinary tract can all create a way for gram negative bacteria to enter the bloodstream. Surgical procedures of the genitourinary tract, intestinal tract, or hepatobiliary tract can also lead to gram negative bacteremia. Pseudomonas and Enterobacter are the most important causes of gram negative bacteremia in the ICU.
Prosthetic cardiac implants (for example artificial heart valves) are especially vulnerable to infection from bacteremia. Prior to widespread use of vaccines, occult bacteremia was an important consideration in febrile children that appeared otherwise well.
Any bacteria that incidentally find their way to the culture medium will also multiply. For example, if the skin is not adequately cleaned before needle puncture, contamination of the blood sample with normal bacteria that live on the surface of the skin can occur. For this reason, blood cultures must be drawn with great attention to sterile process. The presence of certain bacteria in the blood culture, such as S taphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli almost never represent a contamination of the sample. On the other hand, contamination may be more highly suspected if organisms like Staphylococcus epidermidis or Cutibacterium acnes grow in the blood culture.
Two blood cultures drawn from separate sites of the body are often sufficient to diagnose bacteremia. Two out of two cultures growing the same type of bacteria usually represents a real bacteremia, particularly if the organism that grows is not a common contaminant. One out of two positive cultures will usually prompt a repeat set of blood cultures to be drawn to confirm whether a contaminant or a real bacteremia is present. The patient's skin is typically cleaned with an alcohol-based product prior to drawing blood to prevent contamination. Blood cultures may be repeated at intervals to determine if persistent—rather than transient—bacteremia is present.
Prior to drawing blood cultures, a thorough patient history should be taken with particular regard to presence of both fevers and chills, other focal signs of infection such as in the skin or soft tissue, a state of immunosuppression, or any recent invasive procedures.
Ultrasound of the heart is recommended in all those with bacteremia due to Staphylococcus aureus to rule out infectious endocarditis.
Bacteremia may also be defined by the timing of bacteria presence in the bloodstream: transient, intermittent, or persistent. In transient bacteremia, bacteria are present in the bloodstream for minutes to a few hours before being cleared from the body, and the result is typically harmless in healthy people. This can occur after manipulation of parts of the body normally colonized by bacteria, such as the mucosal surfaces of the mouth during tooth brushing, flossing, or dental procedures, or Cystoscopy or Colonoscopy. Intermittent bacteremia is characterized by periodic seeding of the same bacteria into the bloodstream by an existing infection elsewhere in the body, such as an abscess, pneumonia, or Osteomyelitis, followed by clearing of that bacteria from the bloodstream. This cycle will often repeat until the existing infection is successfully treated. Persistent bacteremia is characterized by the continuous presence of bacteria in the bloodstream. It is usually the result of an infected heart valve, a central line-associated bloodstream infection (CLABSI), an infected blood clot (suppurative thrombophlebitis), or an infected Vascular bypass. Persistent bacteremia can also occur as part of the infection process of typhoid fever, brucellosis, and Meningitis. Left untreated, conditions causing persistent bacteremia can be potentially fatal.
Bacteremia is clinically distinct from sepsis, which is a condition where the blood stream infection is associated with an inflammation response from the body, often causing abnormalities in Fever, heart rate, breathing rate, blood pressure, and white blood cell count.
The treatment of bacteremia should begin with empiric antibiotic coverage. Any patient presenting with signs or symptoms of bacteremia or a positive blood culture should be started on intravenous antibiotics. The choice of antibiotic is determined by the most likely source of infection and by the characteristic organisms that typically cause that infection. Other important considerations include the patient's history of antibiotic use, the severity of the presenting symptoms, and any allergies to antibiotics. Empiric antibiotics should be narrowed, preferably to a single antibiotic, once the blood culture returns with a particular bacteria that has been isolated.
The antibiotic treatment of choice for streptococcal and enteroccal infections differs by species. However, it is important to look at the antibiotic resistance pattern for each species from the blood culture to better treat infections caused by resistant organisms.
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