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.
Think of it this way: incidence provides us with information about the current risk of getting a certain disease, while prevalence tells us how many people are living with the condition, regardless of when (or whether) they've been diagnosed with it.