Figure 1.

Selection of cases and controls. For these analyses, we excluded additional subjects from the original study (86 cases and 213 controls) for the following reasons: 61 cases and 17 controls were found to have developed an exclusion criterion during follow-up (after September 1 of their study year). Additional people had used an immunosuppressive medication during baseline (23 cases, 29 controls). Two cases were discovered on further review to have been hospital-acquired. The other 167 controls were dropped because their matched case was excluded for one of the above reasons.