Note: Attached documents contain full case definition and two different control definitions. One is for controls with 2 years of follow up, the other for controls with 1 year of follow up. All available controls with 2 years of follow up were used in Vanderbilt's study. The control population was supplemented by controls with only 1 year of follow up. At the time of study, many of the available controls had experienced their qualifying events somewhat recently and 2 years had not yet passed for full follow up.