Eleven patients have become infected due to dirty equipment despite the NHS trust knowing of an issue for several years.
A report from the Worcestershire Acute Hospitals Trust noted two separate incidents where patients got infected with bacteria - one involving seven patients and a second involving four patients.
All became infected due to problems with the decontamination of equipment in the endoscopy unit at Alexandra Hospital in Redditch.
The report said the machines used for decontaminating the equipment had been in place for more than eight years and were "overdue for replacement".
It said: "In addition, the environment of the endoscopy unit is outdated and due to the environment there is no clear separation between clean and dirty routes.
"The environmental issues including the age of the equipment have been on the directorate and divisional risk registers for a number of years."
In March, water sampling revealed bacteria growth and "two probable cross-infection" incidents among patients undergoing endobronchial biopsy to their lungs.
In the first incident, samples from seven patients grew the bacteria Pseudomonas. The bug can be harmless but can cause serious problems in patients who are weak because of illness, surgery or treatment.
It is one of the main causes of pneumonia in patients who are on ventilation machines, while patients with wounds may develop dangerous infections of the blood, bone or urinary tract.
The second incident occurred from mid-June to early July, when a different bug, Serratia, was isolated from four patients.
They had been examined with a wet scope instead of a dry scope from the drying cabinet, the report said.
Serratia particularly thrives in moist conditions and can cause pneumonia and other infections.
Despite the problems, the report, dated late last month, said some decontamination - namely of gastrointestinal equipment - continues at the endoscopy unit.
"This is because gastrointestinal scopes access a contaminated body cavity, so the risk to the patient is slightly less," the report said.
However, it said the "hazard of possible transmission of a highly resistant organism remains", and has already occurred in another hospital in the West Midlands.
The report said "we have to consider that we are approaching the point" where the decontamination facilities should no longer be used at all.
The report is from the Trust Infection Prevention and Control Committee and was obtained under the Freedom of Information Act by the Health Service Journal (HSJ).
An endoscopy is a procedure to examine the inside of the body using a thin tube and a camera.