Means of Transmission

Direct Transmission

the spread of infection through person-to-person contact

Indirect Transmission

the spread of infection through an intermediary source

Portal of Exit

the site from which an infectious agent leaves its host (e.g., skin lesions, respiratory passages)

Portal of Entry

the site through which an infectious agent enters a new host (e.g., respiratory system, mouth, wounds)

Inapparent Infection

an infection that does not show clinical symptoms but can still be transmitted

Incubation Period

the time interval between exposure to an infectious agent and the first appearance of signs or symptoms

Herd Immunity

immunity of a population against an infectious disease when a large proportion is immune, protecting those who are not

Generation Time

the time interval between the lodging of an agent in a host and the time of maximum communicability

Colonization

when an infectious agent multiplies on a host's surface without invoking an immune response or illness

Iceberg Concept of Infection

the idea that active clinical disease represents only a small proportion of total infections, with most being subclinical

Vehicle

an inanimate intermediary (e.g., contaminated water, food, blood) that transmits an infectious agent

Fomite

an inanimate object (e.g., doorknob, clothing) that can carry and transmit infectious agents

Vector

a living insect or animal that transmits an infectious agent from one host to another

Attack Rate

the proportion of a population that becomes ill over a short period during an outbreak

Secondary Attack Rate

the spread of disease within a household or other closed group after initial introduction

Case Fatality Rate (CFR)

the proportion of individuals with a specific disease who die from it

Five Steps of Outbreak Investigation

1. Define the problem, 2. Appraise existing data, 3. Formulate a hypothesis, 4. Test the hypothesis, 5. Draw conclusions and formulate practical application