What is the difference between the 'incidence' of a disease and the
'prevalence' of a disease?

Hi! Thanks for the question.

Our first link provides a simplistic explanation of the difference
between prevalence and incidence of a disease.

Prevalence - "the probability of currently having a disease without
regard to time of onset. Dividing the number of people who currently
have the disease by the number of people in the study population
yields the prevalence."

Incidence - "the probability of developing a disease within a
specified time period. Incidence is calculated by dividing the number
of people who developed the disease in the time period by the number
of people who did not have the disease at the beginning of the time
period."

"Remember, incidence means NEW. Prevalence means ALL."

"Rates Dealing with the Frequency of Disease"
http://research.med.umkc.edu/tlwbiostats/rates.html

Our next article meanwhile has a deeper explanation which includes the
formula for calculating both prevalence and incidence.

"Prevalence - the measure of a condition in a population at a given
point in time (in this document referred to as point prevalence)."

"Prevalence can also be measured over a period of time (e.g. a year).
This second type of prevalence is called period prevalence; it is a
combination of point prevalence and incidence. The latter is the most
common measure of prevalence used in MCHP studies."

"Incidence - the number of new occurrences of a condition (or disease)
in a population over a period of time."

"The incidence rate uses new cases in the numerator; individuals with
a history of a condition are not included. The denominator for
incidence rates is the population at risk."

"Prevalence and Incidence"
http://www.umanitoba.ca/centres/mchp/concept/dict/prev_incidence.html

Search terms used:  
difference incidence prevalence disease
 
I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
 
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Regards, 
Easterangel-ga

Your answer could not have been better. It is concise and precise. Thank you.