  De-identification of electronic health records (EHR) is a vital step towards
advancing health informatics research and maximising the use of available data.
It is a two-step process where step one is the identification of protected
health information (PHI), and step two is replacing such PHI with surrogates.
Despite the recent advances in automatic de-identification of EHR, significant
obstacles remain if the abundant health data available are to be used to the
full potential. Accuracy in de-identification could be considered a necessary,
but not sufficient condition for the use of EHR without individual patient
consent. We present here a comprehensive review of the progress to date, both
the impressive successes in achieving high accuracy and the significant risks
and challenges that remain. To best of our knowledge, this is the first paper
to present a complete picture of end-to-end automatic de-identification. We
review 18 recently published automatic de-identification systems -designed to
de-identify EHR in the form of free text- to show the advancements made in
improving the overall accuracy of the system, and in identifying individual
PHI. We argue that despite the improvements in accuracy there remain challenges
in surrogate generation and replacements of identified PHIs, and the risks
posed to patient protection and privacy.
