A Birmingham health trust has written to nearly 600 patients after thieves stole diary sheets during a break-in at a district nurse's home.
The paperwork was in the woman's hand-bag, which was among the items taken from her south Birmingham home by masked raiders between 5am and 5.30am on Sunday.
Details of patients' names and addresses were on the stolen sheets, used to help district nurses plan their appointments.
The district nurse, who was based at Hollymoor Health Centre, near Rubery, has not been named.
Last night South Birmingham Primary Care Trust revealed an internal investigation was being launched into how community-based teams keep patient information secure.
In a statement, the trust said letters had been sent "to patients on the district nurse team list since April 2007."
Letters were sent out on Wednesday and Thursday to about 600 patients who have been visited by Northfield district nursing team since last April.
Moira Dumma, the PCT's chief executive, said: "We want to reassure people that this is a precaution and we are doing all we can to support those involved.
"South Birmingham PCT, West Midlands Police and Birmingham City Council take patient safety and data protection very seriously and have worked together to write to everyone concerned."
Concerned patients or relatives can call a special advice hotline set up by the PCT on 0800 389 8391.
Two Birmingham men, aged 18 and 21, have been arrested by police and are currently helping officers with their inquiries.
Some of the stolen sheets have since been recovered but a number are still missing.
Rick Roberts, the PCT's medical director, said: "Some of the missing sheets have been retrieved as they appear to have been discarded by the offenders as they made off.
"Trust staff and police officers also visited about 25 of the most vulnerable patients to make them aware of the situation.
"We are reviewing how district nurses use records as a result of this incident, there will be an internal investigation which I'm due to receive a report on next week."
He added that, as part of the NHS Connecting for Health IT project, district nurses may be equipped with a PDA or BlackBerry in future to reduce paperwork and keep patient information encrypted.