Rapid diagnosis of bloodstream infections

Bloodstream infection (BSI) refers to a systemic inflammatory response syndrome caused by the invasion of various pathogenic microorganisms and their toxins into the bloodstream.

The course of the disease is often characterized by activation and release of inflammatory mediators, causing a series of clinical symptoms such as high fever, chills, tachycardia shortness of breath, rash and altered mental status, and in severe cases, shock, DIC and multi-organ failure, with a high mortality rate. acquired HA) sepsis and septic shock cases, accounting for 40% of cases and approximately 20% of ICU acquired cases. And it is closely associated with poor prognosis, especially without timely antimicrobial therapy and focal control of infection .

Classification of bloodstream infections according to the degree of infection

Bacteraemia

The presence of bacteria or fungi in the bloodstream.

Septicemia

The clinical syndrome caused by the invasion of pathogenic bacteria and their toxins into the bloodstream, is a serious systemic infection.

Pyohemia

Life-threatening organ dysfunction caused by dysregulation of the body’s response to infection.

Of greater clinical concern are the following two associated infections.

Special  Catheter-associated bloodstream infections

Bloodstream infections associated with catheters implanted in blood vessels (e.g., peripheral venous catheters, central venous catheters, arterial catheters, dialysis catheters, etc.).

Special  Infective endocarditis

It is an infectious disease caused by the migration of pathogens to the endocardium and heart valves, and is characterized by the formation of redundant organisms in the valves as a form of pathological damage, and by embolic infection metastasis or sepsis due to redundant organism shedding.

Dangers of bloodstream infections：

A bloodstream infection is defined as a patient with a positive blood culture and signs of systemic infection. Bloodstream infections can be secondary to other sites of infection such as lung infections, abdominal infections, or primary infections. It has been reported that 40% of patients with sepsis or septic shock are caused by bloodstream infections [4]. It is estimated that 47-50 million cases of sepsis occur worldwide each year, causing more than 11 million deaths, with an average of about 1 death every 2.8 seconds [5].

Available diagnostic techniques for bloodstream infections

01 PCT

When systemic infection and inflammatory reaction occur, the secretion of calcitoninogen PCT increases rapidly under the induction stimulation of bacterial toxins and inflammatory cytokines, and the level of serum PCT reflects the serious state of the disease and is a good indicator of prognosis.

0.2 Cells and adhesion factors

Cell adhesion molecules (CAM) are involved in a series of physiopathological processes, such as immune response and inflammatory response, and play an important role in anti-infection and serious infection. These include IL-6, IL-8, TNF-a, VCAM-1, etc.

03  Endotoxin, G test

Gram-negative bacteria entering the bloodstream to release endotoxin can cause endotoxemia; (1,3)-β-D-glucan is one of the main structures of the fungal cell wall and is significantly increased in fungal infections.

04  Molecular Biology

DNA or RNA released into the blood by microorganisms is tested, or after a positive blood culture.

05  blood culture

Bacteria or fungi in blood cultures are the “gold standard”.

Blood culture is one of the simplest, most accurate and most commonly used methods to detect bloodstream infections and is the pathogenic basis for confirming bloodstream infections in the body. Early detection of blood culture and early and proper antimicrobial therapy are the primary measures that should be taken to control bloodstream infections.

Blood culture is the gold standard for the diagnosis of bloodstream infection, which can accurately isolate the infecting pathogen, combine with the identification of drug sensitivity results and give the correct and accurate treatment plan. However, the problem of long positive reporting time for blood culture has been affecting the timely clinical diagnosis and treatment, and it has been reported that the mortality rate of patients not treated with timely and effective antibiotics increases by 7.6% per hour after 6 hours of the first hypotension .

Therefore, the current blood culture and identification of drug sensitivity for patients with suspected bloodstream infections mostly use a three-tier reporting procedure, namely: primary reporting (critical value reporting, smear results), secondary reporting (rapid identification or/and direct drug sensitivity reporting) and tertiary reporting (final reporting, including strain name, positive alarm time and standard drug sensitivity test results) [7]. The primary report should be reported to the clinic within 1 h of the positive blood vial report; the tertiary report is advisable to be completed as soon as possible (generally within 48-72 h for bacteria) depending on the laboratory situation.