Sepsis: causes, signs, diagnosis, treatment and prevention

How sepsis develops

Sepsis begins when a pathogen—bacteria, virus or fungus—evades local defences and triggers a widespread immune reaction. The normally protective immune response becomes dysregulated, causing inflammation, blood clotting abnormalities and impaired circulation. This process can interfere with oxygen delivery to organs and lead to organ dysfunction. The immune system’s role is central; read more about immune responses at the immune system. When a microbe has entered the body or blood, it may be called a pathogen; see pathogen and when it reaches the bloodstream this is termed bacteremia or septicemia in many cases.

Common sources and types

Sepsis can follow infections in many body sites. Common origins include the lungs (pneumonia), urinary tract, abdomen, skin and surgical wounds. Specific terms describe pathogens in blood: bacteremia for bacteria, viremia for viruses and fungemia for fungi. Any of these can precipitate sepsis if the host response becomes uncontrolled.

Signs, diagnosis and assessment

Suspect sepsis when an infection is accompanied by signs such as fever or low temperature, fast heart rate, rapid breathing, confusion or reduced urine output. Clinicians assess organ function, circulation and oxygenation, often using scoring systems and laboratory tests. Blood cultures and imaging are commonly used to identify the source and guide therapy. Because sepsis is a medical emergency, prompt recognition is essential—see guidance linked at emergency care.

Treatment and supportive care

Early treatment focuses on controlling the infection and supporting failing organs. Typical measures include timely antibiotics, surgical or procedural source control when needed, intravenous fluids, and cardiovascular support such as vasopressors if blood pressure remains low. Respiratory or renal support may be required in intensive care. The overall strategy is to treat the cause while stabilizing organ function and preventing complications.

Prevention, prognosis and notable distinctions

Preventing infections through vaccination, hygiene, safe procedures and early treatment of localized infections reduces sepsis risk. Prognosis varies: age, underlying health, the infection source and how quickly treatment begins all influence outcomes. Distinct concepts to remember: septicemia refers specifically to blood poisoning, bacteremia/viremia/fungemia name the organism type, and sepsis denotes the harmful host response leading to organ dysfunction.

Further information and resources

• General sepsis information
• Resources on infections
• Immune system basics
• Pathogen overview
• Bloodstream infections and terminology
• Bacteremia
• Viremia
• Fungemia
• Emergency response to suspected sepsis