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.
The terms incidence and prevalence refer to the number of people who have a particular medical condition. Incidence means the number of people who are newly diagnosed with a condition, while prevalence includes newly diagnosed people, plus people who were diagnosed in the past, and, if the information is obtainable, people who haven't been diagnosed.