A bloodstream infection (BSI) is a medical condition characterized by the presence of bacteria, fungi, or other pathogens circulating within the blood. The bloodstream is ordinarily sterile, but once microbes enter, they are transported throughout the body, reaching distant organs and tissues. This rapid, widespread distribution means a localized infection has become systemic. A BSI requires immediate medical evaluation and intervention.
How Infections Enter the Bloodstream
Microorganisms gain access to the circulatory system through a primary site of infection, which serves as a portal of entry. Common sources include the respiratory tract, where bacterial pneumonia allows pathogens to cross into the blood vessels surrounding the lungs. The urinary tract is another frequent source, as severe infections, particularly those affecting the kidneys, can escalate and spill bacteria into the bloodstream.
Infections of the skin and soft tissues, such as cellulitis or abscesses, offer a route for microbes to enter the circulation. Infections originating within the abdominal cavity, such as appendicitis or diverticulitis, can also introduce bacteria into the blood. When the immune system at these primary sites is overwhelmed, the body’s defenses fail to contain the pathogens.
Certain conditions significantly increase susceptibility to developing a bloodstream infection. People with chronic diseases like diabetes or kidney failure often have a diminished immune response, making them less able to fight off localized infections. Elderly individuals and those receiving immunosuppressive therapies are also at a higher risk.
Indwelling medical devices provide a direct pathway for microbes to bypass the body’s natural barriers. These include central venous catheters, urinary catheters, and mechanical ventilators, which can introduce pathogens or harbor existing colonies. Infections acquired in a healthcare setting are often associated with these devices and contribute significantly to bloodstream infections.
Key Indicators Requiring Urgent Attention
When an infection enters the bloodstream, the body initiates an inflammatory response that results in systemic signs of illness. A common early indicator is a persistent high fever, typically above 100.9°F (38.3°C), often accompanied by shaking and chills. Conversely, some individuals, especially the elderly or those with compromised immunity, may present with an abnormally low body temperature (hypothermia).
The circulatory and respiratory systems react to the microbial invasion and resulting inflammation. This is often seen as a rapid heart rate (tachycardia) and an increased breathing rate (tachypnea). These physiological changes occur as the body struggles to maintain oxygen delivery and clear carbon dioxide, signaling a body-wide state of stress.
Changes in mental status are a concerning sign, indicating the systemic response is affecting the brain and nervous system. These changes reflect reduced blood flow or oxygen delivery to the brain and can manifest quickly. Anyone exhibiting these changes along with other signs of infection requires immediate medical evaluation.
- Confusion
- Delirium
- Disorientation
- Extreme sleepiness
A bloodstream infection often triggers sepsis, a form of organ dysfunction caused by the body’s dysregulated response to the infection. Sepsis is caused not by the germs themselves, but by the chemical cascade released by the immune system. This systemic inflammation causes blood vessels to dilate and leak, leading to a drop in blood pressure (hypotension).
This drop in blood pressure results in poor perfusion, meaning blood flow to the organs is insufficient to meet metabolic needs. Signs of organ dysfunction include reduced or absent urine output, indicating kidney distress, or mottled, discolored skin, which signals poor circulation. Recognizing these systemic indicators is important because the risk of long-term organ damage increases with every hour treatment is delayed.
Confirming the Diagnosis and Starting Treatment
Once a bloodstream infection is suspected based on the patient’s signs, medical intervention begins immediately with diagnostic tests. The definitive procedure for identifying the pathogen is the collection of blood cultures. This involves drawing blood samples and incubating them in special bottles to allow any microbes present to multiply.
It is standard practice to collect blood cultures before administering antibiotics, as the drugs can interfere with the growth of the organisms in the lab. Supporting laboratory tests are also performed to indicate the severity of the systemic response and tissue oxygenation.
- Complete blood count
- Analysis of inflammatory markers
- C-reactive protein
- Lactate
Because a bloodstream infection progresses rapidly, treatment cannot wait for the two or more days required for culture results. Therefore, the immediate strategy involves starting empirical antibiotic therapy, meaning broad-spectrum antibiotics are given to target the most likely types of bacteria. This initial choice is based on the patient’s source of infection, medical history, and local resistance patterns.
As soon as the blood culture identifies the specific pathogen and its susceptibility to drugs, treatment is shifted to a more targeted, narrow-spectrum antibiotic. This approach ensures the most effective therapy while helping to prevent antibiotic resistance. The goal is to maximize microbial clearance while minimizing unnecessary exposure to powerful drugs.
Supportive care measures are important for managing the effects of sepsis and preventing organ failure. Patients are often given intravenous fluids to maintain adequate blood pressure and circulation. If fluids alone are not sufficient, medications called vasopressors are administered to constrict blood vessels and raise the blood pressure.
Monitoring organ function is continuous. Interventions such as mechanical ventilation may be used to support the lungs if breathing is impaired. If the kidneys begin to fail, temporary dialysis may be required to clear waste products from the blood. These supportive measures aim to stabilize the patient’s vital functions while antibiotic therapy eliminates the underlying infection.