The discovery of medical notes from Royal Shrewsbury Hospital was made by a jogger near Grange Pools, Stirchley, on Monday morning.
It comes a month after sensitive medical letters were wrongly sent to a patient instead of a doctors' surgery.
In this latest data breach, the notes included names, ages, medical history, drug treatment and details of who patients live with.
The confidential nursing notes from Ward 24 have details for 15 patients, including conditions they suffer from, operations they were in for, whether they use a wheelchair or a stick, as well as details of "not for resuscitation" orders. Evidence of the notes, which have been seen by the Shropshire Star, are dated March 2023.
A source close to the finder of the documents said: "My major concern is when things like this happen, rather than admit what went wrong and try and prevent it from happening again, there may be a culture of covering this up [within Shrewsbury and Telford Hospital NHS Trust - SaTH].
"It clearly states 'this printout contains confidential information and you are responsible for its continued confidentiality'. I'd be mortified if I thought my personal details were handled in such a careless manner."
It is understood that SaTH requested that the notes were dropped off so an inquiry could be conducted.
A spokesperson for the SaTH, said: “We would like to thank the individual for alerting us to this issue and we are currently investigating.
“We take our responsibility to maintain the confidentiality of patients, staff and others very seriously. When a data breach is identified, we will undertake a full review, contact those who may be affected, and do all that we can to learn how to prevent re-occurrence in the future.”
The incident saw a total of 11 letters for patients sent to another patient awaiting an update on his own treatment.
All the letters were contained in one envelope, and included updates on different individual patients' medical treatments.