This included each person's name, identification number, phone number and address, HIV test results and related medical information.
Brochez, who lived in Singapore between January 2008 and June 2016, obtained the documents from Ler Teck Siang, his Singaporean partner who worked as the head of MOH's National Public Health Unit from March 2012 to May 2013.
According to the Straits Times, a Singaporean newspaper, Brochez submitted a blood sample from Ler as his own, after testing positive for HIV in 2008.
His partner, the former health official, is serving a 24-month sentence on charges of abetting the man to commit cheating, and of providing false information to the authorities.
"We are sorry for the anxiety and distress caused by this incident". Although the Ministry contacted the affected individuals, the public was not informed of this discovery.
However, as far back as in May 2016, MOH has already received information that Farrera-Brochez possessed the confidential data from its HIV Registry.
Access to the information has been blocked but it is still in the possession of the person who leaked it - and could be disclosed again, the ministry warned.
It said Brochez worked in Singapore for a period before he was jailed for several drug and fraud-related offenses and deported a year ago.
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Last week, it learned that he could still be in possession of the data, the ministry said.
Permanent Secretary of Heath Chan Heng Kee told reporters at a media briefing on Monday that of the 5,400 Singaporeans whose information had been leaked, 1,900 of them had already died, Channel News Asia reported. From June 27 to July 4 past year, hackers infiltrated the computers of SingHealth and stole the personal particulars of 1.5 million patients, including Prime Minister Lee Hsien Loong.
Brochez is now under police investigation, and the authorities are seeking assistance from their foreign counterparts, according to the ministry statement, which did not specify any country.
"Police will not hesitate to take stern action, including prosecution, against those who have breached the OSA".
"While access to the confidential information has been disabled, it is still in the possession of the unauthorised person, and could still be publicly disclosed in the future", it said.
June 2016: Ler was charged for offences under the Penal Code and OSA.
Gan further said that a hotline has been set up to assist affected individuals. The American was deported in May 2018, after which the Health Ministry was notified that he still held on to some records from 2016, though, the data then did not appear to have been exposed.
While the MOH statement doesn't give an exact motive for the leak, it does state that it was the result of "mishandling of information by Ler, who is suspected of not having complied with the policies and guidelines on the handling of confidential information".
Sentenced to two years in jail, Ler is appealing against the sentence, with the hearing scheduled for March.