1 For best results from your flask, before use, pre-fill for about 3 minutes, using either hot water for hot drinks or cold water for chilled drinks. 2  Never use a microwave or conventional oven to pre-heat your flask.  If your flask has not been used for some time, rinse with warm water to remove any residual odours.
2. : the degree to which something is prevalent; especially: the percentage of a population that is affected with a particular disease at a given time.
For example, the prevalence of obesity among American adults in 2001 was estimated by the U. S. Centers for Disease Control (CDC) at approximately 20.9%. Prevalence is a term which means being widespread and it is distinct from incidence.Prevalence is a measurement of all individuals affected by the disease at a particular time, whereas incidence is a measurement of the number of new individuals who contract a disease during a particular period of time.t can be used for statistics on the occurrence of chronic diseases. This is in contrast to period prevalence which is a measure of the proportion of people in a population who have a disease or condition over a specific period of time, say a season, or a year.