Write SQL query to solve given problem: What is the prevalence rate of the patients' diseases started on 9th May 2014?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T2."PREVALENCE RATE" FROM conditions AS T1 INNER JOIN all_prevalences AS T2 ON lower(T1.DESCRIPTION) = lower(T2.ITEM) WHERE T1.START = '2014-05-09'