Pathogenesis - the way in which the disease is caused, or in other words the chain of events leading to disease.

Reproduction number (basic) – the average number of new (secondary) cases, or successful transmissions, per case in a totally susceptible population.

Reproduction number (net) - the average number of new (secondary) cases, or successful transmissions, per case in the population, taking into account that some of the population is not susceptible.

Reservoir host - a passive carrier of the infectious organism that is not harmed by the organism, but can be a source of infection for other individuals.

Risk ratio – the risk of acquiring the disease in individuals who were exposed to a particular factor compared to those who were not exposed to the factor

RNA – ribonucleic acid - the genetic material contained by some viruses, similar to DNA in humans.

Sensitivity – the proportion of actual/true cases of disease that are identified by the tool (e.g. case definition; a sensitive case definition would be one that successfully diagnoses all or most cases of disease, so called true positives).

Specificity – the proportion of actual/true non-cases that are identified by the tool (e.g. case definition; a specific case definition would be one that more successfully excludes individuals who do not really have the disease, so called false positives).

Note that the particular epidemiological terms used by different authors in different studies can vary, so you may come across other variations of some of these terms in your reading.