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.
Asker's rating. Report Abuse. prevalence of a disease refers to the proportion of a set that has a disease while its incidence refers to the number of newly diagnosed cases.for example the prevalence of EVD in Nigeria is 7/160,000000 while its incidence as at now is 7.