What is the medical term for an infection?

Medical Term for an Infection

The medical term for an infection is simply "infection," which is defined as a microbial invasion of host tissue that results in a host response and potential tissue damage. 1

Core Definition and Classification

Infection represents the presence and multiplication of microorganisms in body tissues that produces an immune or inflammatory response. 1 This differs from mere microbial exposure or colonization, where organisms are present but not causing active disease. 2

Key Terminology in Infectious Disease

The basic lexicon includes several related but distinct terms that describe different states of host-microbe interaction: 2

• Exposure: Contact with a microorganism without necessarily establishing infection 2
• Colonization: Presence of microorganisms without tissue invasion or immune response 2
• Infection: Microbial invasion with host tissue response 1, 2
• Disease: Infection that produces clinical symptoms and pathology 2, 3

Specific Types of Infections by Anatomical Location

Peritonitis (Abdominal Infection)

Peritonitis is inflammation of the peritoneum that can be infectious or sterile, with infectious peritonitis classified into primary, secondary, and tertiary forms. 1

Cellulitis (Skin Infection)

Cellulitis refers to diffuse, spreading infection of the dermis and subcutaneous tissue, while erysipelas affects the upper dermis and superficial lymphatics. 1, 4

Endocarditis (Heart Infection)

Infective endocarditis (IE) is an endovascular microbial infection of intracardiac structures facing the blood. 1

Classification by Acquisition Setting

Healthcare-Associated Infection (HCAI)

Healthcare-associated infection (HCAI) is the modern term for infections acquired during healthcare delivery, replacing the older term "nosocomial infection." 1 This includes: 1, 5

• Hospital-acquired infections (developing >48 hours after admission) 5, 6
• Infections in nursing facility residents 1, 5
• Infections following recent hospitalization within 90 days 1, 5
• Infections related to aggressive home medical therapies within 30 days 1, 5

Community-Acquired Infection

Infections developing outside healthcare settings or within 48 hours of hospital admission are termed community-acquired infections. 1

Clinical Severity Classifications

Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, represented by an increase in the Sequential Organ Failure Assessment (SOFA) score of 2 points or more. 1

Septic Shock

Septic shock is a subset of sepsis requiring vasopressor support to maintain mean arterial pressure ≥65 mmHg and serum lactate >2 mmol/L despite adequate fluid resuscitation. 1

Common Pitfalls in Terminology

Critical distinction: The term "infection" should not be confused with "colonization" (organism present without tissue invasion) or "contamination" (organism present in specimen but not in patient). 5, 2 This distinction is essential for appropriate antibiotic use, as treating colonization rather than true infection drives antimicrobial resistance. 5

Bacteremia vs. Septicemia: While historically used interchangeably, bacteremia specifically refers to bacteria in the bloodstream, while septicemia implies systemic infection with clinical toxicity. 1 Modern terminology favors "bacteremia" with severity classified using sepsis definitions. 1