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.
It is thus a proportion, rather than a rate, although you may sometimes see it called a rate.. Prevalence provides a good way to indicate the burden of disease in a population. It is influenced by the incidence and by the duration of the condition: under most circumstances, prevalence = incidence Ã disease duration. MORTALITY RATE. The number of deaths per thousand population per year: in effect, the incidence of death in a population.