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.
1 âPrevalenceâ is the proportion of a population who have (or had) a specific characteristic in a given time period â in medicine, typically an illness, a condition, or a risk factor such as depression or smoking. Period prevalence is the proportion of a population that has the characteristic at any point during a given time period of interest. â 2 Past 12 monthsâ is a commonly used timeframe.