The Messenger revealed on Friday that passer-by Nicola Barrett spotted the documents blowing around on the pavement in Chatham Hill.
Nicola Barrett, from Gillingham, found confidential South East Coast Ambulance Service documents on a path in Chatham
The documents included one with the name, address and contact details for a teenager who had tried to take her own life and details of a woman found dead in bed.
Big Brother Watch deputy director Emma Carr said: “I think the fact it was not just one document relating to a single person tells you that a serious data breach occurred here and South East Coast Ambulance Service has some serious questions to answer.
“If that was me, I would be incredibly annoyed with the ambulance service for improperly disclosing these documents.
“They are very sensitive issues, especially if someone has tried to take their life; they are clearly not in a state to hear this sort of news.”
Big Brother Watch has called for apologies to those affected in addition to a full explanation about how it happened and what remedies the South East Coast Ambulance Service were taking to ensure it did not happen again.
Ms Carr added: “The Information Commissioner’s office should be contacted as well so there can be an external investigation to see whether the system should be changed.”
As well as details about patients’ medical treatment and diagnosis, the documents also included addresses and contact details of next of kin.
Ms Carr said: “When you have personal details in documents like this, it also opens up people to the risk of fraud.
“If people got hold of this information and wanted to burgle a home then an elderly and vulnerable person would be a good target.
“There are genuine concerns about people getting hold of this information and committing any wrongdoing – this isn’t a small data breach, it is a very serious one and we should be thankful that an honest member of the public found these documents first.”
"A serious data breach occurred here" - Big Brother Watch
The South East Coast Ambulance Service NHS Foundation Trust (SECAmb) has launched an investigation into the matter.
A spokesperson said: “We safely handle data relating to well in excess of 500,000 999 calls every year and any breaches are extremely rare. We believe this to be an isolated and unusual occurrence, which we will investigate thoroughly.
“In addition, we are currently in the process of looking into the introduction of an electronic version of these patient forms.”