Evaluating the re-identification risk of a clinical study report anonymized under EMA Policy 0070 and Health Canada Regulations

BACKGROUND: Regulatory agencies, such as the European Medicines Agency and Health Canada, are requiring the public sharing of clinical trial reports that are used to make drug approval decisions. Both agencies have provided guidance for the quantitative anonymization of these clinical reports before they are shared. There is limited empirical information on the effectiveness of this approach in protecting patient privacy for clinical trial data. METHODS: In this paper we empirically test the hypothesis that when these guidelines are implemented in practice, they provide adequate privacy protection to patients. An anonymized clinical study report for a trial on a non-steroidal anti-inflammatory drug that is sold as a prescription eye drop was subjected to re-identification. The target was 500 patients in the USA. Only suspected matches to real identities were reported. RESULTS: Six suspected matches with low confidence scores were identified. Each suspected match took 24.2 h of effort. Social media and death records provided the most useful information for getting the suspected matches. CONCLUSIONS: These results suggest that the anonymization guidance from these agencies can provide adequate privacy protection for patients, and the modes of attack can inform further refinements of the methodologies they recommend in their guidance for manufacturers.